# Building a workshop in an old stone built barn



## David66 (8 Aug 2022)

As the title says, I plan to build a workshop in an old stone barn, and I need some advice/thoughts. I am inexperienced when it comes to building etc.

This is a picture of the current interior. 

As you can see, it's rough stone, with a cobbled floor. The floor is very uneven, and drops about 18" from left to right in the picture. The wall bulges at the far left corner (where the boulder is - tried to move it, but can't !!). The roof is new, and sound, but there is water seeping in the left (back) wall, and the floor is damp.

I'm not looking for a liveable space (!), just somewhere I can set up a work bench, couple of saws and some storage on the walls.

Current plan is to drop studs from the rafters to the floor on each side of the barn, run a 4x2 along the bottom of the studs on each side, and then floor joists between the 4x2s - keeping everything as level as possible. Cover the floor joists with 18mm OSB, and the studs with 12mm OSB. So far, so simple, however, I have a few questions.

First, the floor joists will span around 3.6m, so will need supported on the (very uneven) floor - I was planning to use off cuts of 4x2 simply fixing the joists to the off cuts, and resting the off cuts on the floor/ground. Will that work? Alternatives? I plan to use treated timber, and paint anything touching the floor with bitumen paint. 

Second, I'm worried about damp from the walls and the floor. Do I need a waterproof lining on the stone walls and the floor?

Finally, if I wanted to insulate (haven't decided yet, but will be pretty cold in winter if I don't) - what would be the best option (I rent the shed and the landlord doesn't want me spraying anything on the walls - so spray foam insulation won't work)?

Thanks a lot for your thoughts.


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## Jameshow (8 Aug 2022)

You could use offcuts perhaps make a t shaped foot to spread the load. Put some felt / slate under to stop damp. 

You could put studs from the floor to the roof and insulation between. With these old buildings it's important to let them breath so leave a gap all round.


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## David66 (8 Aug 2022)

Jameshow said:


> You could use offcuts perhaps make a t shaped foot to spread the load. Put some felt / slate under to stop damp.
> 
> You could put studs from the floor to the roof and insulation between. With these old buildings it's important to let them breath so leave a gap all round.


When you say "felt" you mean the stuff you use on shed roofs? Any rule of thumb on the gap to leave?


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## Jameshow (8 Aug 2022)

David66 said:


> When you say "felt" you mean the stuff you use on shed roofs? Any rule of thumb on the gap to leave?


Yes but bitumen paint will do just as well. 

I'd use 4x2 studs and 2" insulation..


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## Spectric (8 Aug 2022)

That would be a great setting for traditional woodworking, one of those treadle lathes and a big stout bench.



David66 said:


> I plan to use treated timber, and paint anything touching the floor with bitumen paint.


If it is that damp also use a DPM on the floor and bring it up the walls, might be an idea to look at semi tanking the building and keep everything off the walls so there is an air gap.


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## David66 (8 Aug 2022)

Spectric said:


> That would be a great setting for traditional woodworking, one of those treadle lathes and a big stout bench.
> 
> 
> If it is that damp also use a DPM on the floor and bring it up the walls, might be an idea to look at semi tanking the building and keep everything off the walls so there is an air gap.


Do I just lay the DPM on the ground under the raised floor, or do I attach it to the raised floor in some way?


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## Spectric (8 Aug 2022)

The DPM is to prevent moisture from the ground coming into contact with the floor or rising up, so I would lay it across the floor and partly up the wall to keep any ground damp from getting to your floor structure which I would not attach the DPM. How damp / wet are the walls ?


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## mikej460 (8 Aug 2022)

I would first find out where the damp is coming from. If it's the roof then get that fixed, check to see if water run off is clearing all walls (use a powerful hose fixed at an angle to a stake to simulate rain). Buy a cheap moisture meter and check around the walls for water ingress then investigate how it's getting in (very often it's run-off from the roof or poor/missing guttering or earth banked on the outside). If you can't find anything obvious then you need to shield the walls and floor, effectively building a bubble inside the barn:
1. Fit a damp proof membrane 1200 gauge/300mu (cheapest is on eBay) and as stated above, buy sufficient to run it at least 300mm up each wall
2. Lay a timber joists supported by treated wooden legs each resting on a treated timber plate to spread the load. 
2. As above build an internal timber frame wall out of 50mm battens between the rafters. Use more horizontal battens on the outside of the vertical ones to strengthen the structure. Staple Tyvek Housewrap all around the walls. This lets moisture out but not in. Make sure the 300mm of DPM is on the outside of the housewrap.
3, Then fix lengths of 3x2 or 4x3 treated timber from rafters to joists 50mm away from the battens/housewrap. These will support your tools/shelving. Nail/screw horizontal lengths (noggins) between each pair of studs to strengthen them. You could leave the new internal walls there or better still clad in OSB3 sheets screwed in to the new stud work.
4. Lay moisture resistant chipboard flooring over the joists
5. Fit PIR insulation in between the rafters and fill any gaps with insulating foam. Leave or clad in OSB3.

I think that's enough for now but once you've decided on a way forward do ask questions at each stage.

I hope this is useful


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## David66 (8 Aug 2022)

Spectric said:


> The DPM is to prevent moisture from the ground coming into contact with the floor or rising up, so I would lay it across the floor and partly up the wall to keep any ground damp from getting to your floor structure which I would not attach the DPM. How damp / wet are the walls ?


They're not running with water, but there is green mould on the stone


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## mikej460 (8 Aug 2022)

David66 said:


> They're not running with water, but there is green mould on the stone


In which case if may be damp from the floor so you might be able to avoid the internal wall build and concentrate on joists raised on a DPM. Another solution would be to build a timber raft directly on top of the DPM.


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## David66 (8 Aug 2022)

mikej460 said:


> I would first find out where the damp is coming from. If it's the roof then get that fixed, check to see if water run off is clearing all walls (use a powerful hose fixed at an angle to a stake to simulate rain). Buy a cheap moisture meter and check around the walls for water ingress then investigate how it's getting in (very often it's run-off from the roof or poor/missing guttering or earth banked on the outside). If you can't find anything obvious then you need to shield the walls and floor, effectively building a bubble inside the barn:
> 1. Fit a damp proof membrane 1200 gauge/300mu (cheapest is on eBay) and as stated above, buy sufficient to run it at least 300mm up each wall
> 2. Lay a timber joists supported by treated wooden legs each resting on a treated timber plate to spread the load.
> 2. As above build an internal timber frame wall out of 50mm battens between the rafters. Use more horizontal battens on the outside of the vertical ones to strengthen the structure. Staple Tyvek Housewrap all around the walls. This lets moisture out but not in. Make sure the 300mm of DPM is on the outside of the housewrap.
> ...


Thank you. Very helpful. 

The roof is sound. Recently replaced, and no sign of any water coming in during recent (very) heavy rain. It's only the back wall that's damp, and I'm pretty sure its earth banked up against that wall that's the problem.

Some follow up questions if I may

1. Does the DPM simply lie on the floor? Do you/how do you attach the 300mm to the wall?

2. When you say a treated timber plate, do you simply mean a piece of (say) treated 2x4, nailed to the upright support in a T shape?

3. So, there would be 2 internal frames - an outer frame against the wall, with Tyvek stapled to it, and the second one 50mm from the Tyvek? Do I attach the first timber frame to the wall, or just one end to the rafters with the other resting on the floor? Does it matter if the timber on the outer frame touches the wall?

4. If I were adding insulation to the walls, would it go between the studs on the 2nd or inner internal frame, before you attach the OSB? How would I fix it to the studs/noggins but at the same time, prevent it touching the Tyvek?

5, Do I need to insulate the floor? Presumably PIR sheets between the floor joists - again, how do you fix the PIR in place, before attaching the flooring - or do you just lay it on the floor?

3. What thickness of OSB would you suggested for the walls/floor/roof?

Apologies for all the questions ... I tend to over think things!!


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## Sandyn (8 Aug 2022)

That looks very like a very old worn out byre. The cows stood on the left, probably for milking. The channel on the floor is where all the [email protected] was washed/brushed away.

You rent it and you are going to spend a considerable amount of money to make it usable? Any possibility you have your own place and space to build a new shed?


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## mikej460 (8 Aug 2022)

I'd consider hiring a digger and digging out the earth and build a french drain behind the wall (basically a trench back filled with shingle). Answers to specific questions are:
1. Yes it just lays on top of the earth floor. You can staple the 300mm sides onto the back of the battens (facing the stone wall)
2. I'd use a square of 5x1 gravel board - it's only there to prevent damaging the dpm and/or the supports sinking
3. Yes there would be 2 internal frames but no you shouldn't attach it to the wall. The idea is to let air flow behind the housewrap to take away damp air.
4. Insulation would go in between the internal studwork not the battens. It shouldn't matter if it touches the housewrap but if you fit insulation you do need a vapour barrier on the inside of the studwork i.e. the workshop side, to stop damp air getting ito your work space. This could be stapled plastic sheet vapor barrier or OSB3 which is moisture proof.
5. If you can afford it then yes, as a cheaper alternative to PIR I've used polystyrene EPS70 slab to good effect in the past.
6. I'd recommend 11mm


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## sawtooth-9 (8 Aug 2022)

Agree with Sandyn


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## David66 (8 Aug 2022)

Sandyn said:


> That looks very like a very old worn out byre. The cows stood on the left, probably for milking. The channel on the floor is where all the [email protected] was washed/brushed away.
> 
> You rent it and you are going to spend a considerable amount of money to make it usable? Any possibility you have your own place and space to build a new shed?


An old Byre is exactly what it is. The main house is a renovated croft, attached to another old byre. I hear you on renting and the cost of renovation! It's a long story. The property is owned by a good friend. He's letting us stay there rent free, on condition that we finish the renovations he started 15 years ago! It's been a VERY steep learning curve!!! There's more to it .... but I won't trouble you all with the detail!


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## TRITON (8 Aug 2022)

Very nice, thats going to look the business when complete. Very traditional and woody.


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## David66 (8 Aug 2022)

TRITON said:


> Very nice, thats going to look the business when complete, but I'll wager its going to be nippy come winter.


Agreed - beginning to think about a wood burning stove .... but I think I'm getting carried away!!


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## TRITON (8 Aug 2022)

I spent many years working in an unheated Butchers, and winters were cold to really cold.
Boss's advice if you're feeling the cold ...

Work harder


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## mikej460 (8 Aug 2022)

David66 said:


> An old Byre is exactly what it is. The main house is a renovated croft, attached to another old byre. I hear you on renting and the cost of renovation! It's a long story. The property is owned by a good friend. He's letting us stay there rent free, on condition that we finish the renovations he started 15 years ago! It's been a VERY steep learning curve!!! There's more to it .... but I won't trouble you all with the detail!


In a nutshell and as phase one I would:
1. Lay a DPM and floor
2. Insulate and board the roof
3. Dig out the soil behind the wall and lay a french drain

Then if you continue to have damp problems build the internal wall system I described.

If you can keep the lovely stone walls that would be a visual bonus but at the expense of useful wall space. There could be a middle ground where you could build a partial stud wall over a cruddy bit if there is one!


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## David66 (8 Aug 2022)

mikej460 said:


> If you can keep the lovely stone walls that would be a visual bonus but at the expense of useful wall space. There could be a middle ground where you could build a partial stud wall over a cruddy bit if there is one!


Interesting - so, build the stud wall on the back wall, where all the damp is, for shelving etc, while keeping the front wall as is


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## mikej460 (8 Aug 2022)

David66 said:


> Interesting - so, build the stud wall on the back wall, where alter damp is, for shelving etc, while keeping the front wall as is


No not that, I'm assuming here that your damp could be fixed by the french drain and new floor. What I mean is that you could preserve the main, more attractive stone walls and use another wall or part wall for storage using internal stud work.

Another point to support roof insulation is that cold damp air condenses on colder metal or cement roof sheets and drips like rain all over your workshop. By insulating and sheathing with osb you can prevent this.


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## David66 (8 Aug 2022)

mikej460 said:


> No not that, I'm assuming here that your damp could be fixed by the french drain and new floor. What I mean is that you could preserve the main, more attractive stone walls and use another wall or part wall for storage using internal stud work.
> 
> Another point to support roof insulation is that cold damp air condenses on colder metal or cement roof sheets and drips like rain all over your workshop. By insulating and sheathing with osb you can prevent this.


Ah, OK. 

TBH, digging out the back wall would be tricky. The main access track is right behind the shed, and about 4' higher than the floor of the shed. On the other side of the track there's rock. I suspect that digging out the wall would mean repositioning the track, which would mean digging out all the rock. And getting a digger in there (4km along a very narrow and steep 4x4 track) wouldn't be cheap!


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## mikej460 (8 Aug 2022)

David66 said:


> Ah, OK.
> 
> TBH, digging out the back wall would be tricky. The main access track is right behind the shed, and about 4' higher than the floor of the shed. On the other side of the track there's rock. I suspect that digging out the wall would mean repositioning the track, which would mean digging out all the rock. And getting a digger in there (4km along a very narrow and steep 4x4 track) wouldn't be cheap!


Wow, ok then unless you can dig a 6ft deep trench down the back of the wall and back fill with pea shingle and a DPM between the shingle and the wall you are a bit stuck. You could still go ahead with phase 1 as I laid out but be prepared for phase 2 - building the internal wall.


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## David66 (8 Aug 2022)

mikej460 said:


> Wow, ok then unless you can dig a 6ft deep trench down the back of the wall and back fill with pea shingle and a DPM between the shingle and the wall you are a bit stuck. You could still go ahead with phase 1 as I laid out but be prepared for phase 2 - building the internal wall.


Is that 6' below floor level? How wide would it need to be?


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## mikej460 (8 Aug 2022)

No, assuming you can't move the road dig 4 feet down plus 2 feet to take water below floor level, I'd make it 450mm across. Bear in mind that a 6ft trench is a potential death trap so use experts to dig this for you. Line the trench with a Geotextile sheet in a U shape with a flap lid to stop soil working it's way in, lay the a DPM down against the wall or get a plasterer or builder to trowel on tanking to the outside of the wall which, if done properly, is very effective and often used to dry out old cellars for example). You could then back fill with a layer of soil to restore the track as long as you don't go above the tanking. I'd encourage you to research this and talk to a couple of good builders.


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## David66 (8 Aug 2022)

mikej460 said:


> No, assuming you can't move the road dig 4 feet down plus 2 feet to take water below floor level, I'd make it 450mm across. Bear in mind that a 6ft trench is a potential death trap so use experts to dig this for you. Line the trench with a Geotextile sheet in a U shape with a flap lid to stop soil working it's way in, lay the a DPM down against the wall or get a plasterer or builder to trowel on tanking to the outside of the wall which, if done properly, is very effective and often used to dry out old cellars for example). You could then back fill with a layer of soil to restore the track as long as you don't go above the tanking. I'd encourage you to research this and talk to a couple of good builders.


Thanks for all your advice. Appreciate you taking the time to explain in such detail. 

I don't think digging down the back of the wall is an option - getting somebody to do that would be expensive, even if I could find somebody (almost impossible in that location). The internal wall solution will be cheaper and easier, as I can (hopefully) do it myself. Only down side I can see (other than additional time and materials), is I'll lose some internal space, around 250mm on each wall (50mm gap to the first wall, 50mm for that wall, 50mm gap to the second wall, 75mm for that wall, plus another 11mm for the OSB). 

Not a disaster!


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## mikej460 (8 Aug 2022)

David66 said:


> Thanks for all your advice. Appreciate you taking the time to explain in such detail.
> 
> I don't think digging down the back of the wall is an option - getting somebody to do that would be expensive, even if I could find somebody (almost impossible in that location). The internal wall solution will be cheaper and easier, as I can (hopefully) do it myself. Only down side I can see (other than additional time and materials), is I'll lose some internal space, around 250mm on each wall (50mm gap to the first wall, 50mm for that wall, 50mm gap to the second wall, 75mm for that wall, plus another 11mm for the OSB).
> 
> Not a disaster!


ok but you don't need some of the gaps you listed only between the 1st (batten/housewrap) and the stud wall. so 50mm wall to wrap, 75mm studwork, 11mm OSB3 so 136mm on each wall. Apols if I confused you, I'm trying to explain a timber frame workshop build working backwards!


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## MCTWoodwork (9 Aug 2022)

Great project, I did something similar in an milking shed where we used to live.. I laid a DPM then a hand mixed concrete floor to level the floor with a builder friend. I also drilled the wall (every 300mm at about a foot high) and filled with a liquid DPM to stop rising damp along with the sheet DPM (Under the concrete). It's not too expensive stuff but worth it. Then as Mike said, I created an internal "room" as he described with studs and noggins and insulation and filled any gaps with expanding foam leaving a small gap on the OSB from floor level to allow it to breathe. Good luck!


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## MCTWoodwork (9 Aug 2022)

Ps - I was referring to the gap between the concrete floor and walls... You obviously won't do that if you create a floating floor. Anyway... Ageing, good luck and sounds like you will have a great space to make pretty things out of wood and lots of sawdust...


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## Adam W. (9 Aug 2022)

@David66 It looks like a massive job and making a shed like that dry enough to keep tools in is going to take a lot of work.

We lived on a very steep slope in the Mendips a while back and I picked up an old 10' garden shed for free to use as the bathroom and then my workshop. 

That's what I would do in your case and leave the stone building to the bats and spiders.


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## David66 (9 Aug 2022)

mikej460 said:


> Another point to support roof insulation is that cold damp air condenses on colder metal or cement roof sheets and drips like rain all over your workshop. By insulating and sheathing with osb you can prevent this.


One thing I didn't mention last night - there are no windows in the shed - all the natural light comes in via transparent panels in the roof (not roof windows, just clear corrugated plastic sheets). So, if I insulate and sheet the roof, there will be large gaps for these sheets - still worth it?


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## David66 (9 Aug 2022)

Adam W. said:


> @David66 It looks like a massive job and making a shed like that dry enough to keep tools in is going to take a lot of work.



Forgive my ignorance - but what's the issue with keeping tools in a shed like this?


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## Adam W. (9 Aug 2022)

Rust.

I have a small stone shed with a thatched roof, it's good for the mower and mixer, but rubbish for woodworking tools.

The thatched roof keeps it dry and is its saving grace and it doesn't have soil banked up against it, but it's still a palace of condensation.


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## David66 (9 Aug 2022)

Adam W. said:


> Rust.


Ah, of course - now I just feel stupid!


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## Adam W. (9 Aug 2022)

Don't, we've all been there at some point.


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## clogs (9 Aug 2022)

if u decide to cover the walls use galv plaster board fixings....
wood is expensive and holds damp where the galv will stop the water getting to the new walls....
it's very easy to make a rough wall straight n level....
as for the floor, I understand the difficulty but I'd be useing a damp proof membrane and the high density foam for insulation and concrete the thing....remember DPM up the walls above the floor as well as an insulation barrier....1" thick will be plenty...it's just to keep the new floor away from the walls.....the insu has many diff thicknesses so easy to get a rough level before the pour.....
PLUS if I were there for a long time I'd put a log fire and back boiler/pump with under floor heating as it's as cold as a Bears "A" hole up there in winter....
if u wanna insu the roof double up on the roof lights as in double glazed...it will swet if single sheets.....dew point....
then just make an internal box around them....wood if u want but I'd use the galv again and insulated plaster board to make it cosy.....
plus nobody I think has mentioned guttering...very importans and make shore the downpipe exit as far away as poss from the building...or....even if u have to dig a stone filled pit/soak away...1m cube will be fine for each down pipe.....u can make it so the road goes over the top if needed...

quite a while ago I did a leaky railway arch for a guy's new workshop...
it was so bad we just built an insulated steel barn type box inside....simples....
good luck....


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## David66 (9 Aug 2022)

clogs said:


> if u decide to cover the walls use galv plaster board fixings....
> wood is expensive and holds damp where the galv will stop the water getting to the new walls....
> it's very easy to make a rough wall straight n level....
> as for the floor, I understand the difficulty but I'd be useing a damp proof membrane and the high density foam for insulation and concrete the thing....remember DPM up the walls above the floor as well as an insulation barrier....1" thick will be plenty...it's just to keep the new floor away from the walls.....the insu has many diff thicknesses so easy to get a rough level before the pour.....
> ...


Thanks clogs. What's "galv plaster board fixings". I googled it but all that came up were screws for fixing into plaster board. I'm guessing its some sort of sheeting material?

I have been thinking about a log burner ... but costs are mounting, and we will only be there for a few years.


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## Jameshow (9 Aug 2022)

David66 said:


> Thanks clogs. What's "galv plaster board fixings". I googled it but all that came up were screws for fixing into plaster board. I'm guessing its some sort of sheeting material?
> 
> I have been thinking about a log burner ... but costs are mounting, and we will only be there for a few years.


Think he means galvanised c studs rather than wood. I'd just use treated timber tbh. 

Concrete slab seems alot of work compared to a wooden floor? 

I'd get a woodburner which you can take with you when you leave. Keep the roof cut out and put back on with flashing when you leave!!


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## MikeJhn (9 Aug 2022)

You will not stop the damp from the wall with earth banked up against it, so control the water that comes through, a gutter of some kind at the bottom of the wall falling away with the natural slope of the floor, then build a wall in front of the existing wall, for the floor just timber 4 x 2 sat up on legs to the desired height, legs sat on tiles or a piece of DPC, use T&G moisture resistant chipboard for the floor or even a good quality plywood, but coat the underside with moisture barrier paint, ventilation of some kind under the floor to dissipate the moisture would be a bonus, just accept you will not stop the damp, but control what is there.

This was the inside of my workshop/barn:


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## David66 (9 Aug 2022)

MikeJhn said:


> You will not stop the damp from the wall with earth banked up against it, so control the water that comes through, a gutter of some kind at the bottom of the wall falling away with the natural slope of the floor, then build a wall in front of the existing wall, for the floor just timber 4 x 2 sat up on legs to the desired height, legs sat on tiles or a piece of DPC, use T&G moisture resistant chipboard for the floor or even a good quality plywood, but coat the underside with moisture barrier paint, ventilation of some kind under the floor to dissipate the moisture would be a bonus, just accept you will not stop the damp, but control what is there.
> 
> This was the inside of my workshop/barn:


Thanks for your advice. Do you have issues in your workshop with rusting tools?


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## Jameshow (9 Aug 2022)

I have a damp workshop if it really rains the floor slab becomes damp, however my tools haven't gone rusty probably because there is a decent amount of timber / shavings hanging around to absorb it.... 

Not that I do any fine work!


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## MikeJhn (9 Aug 2022)

David66 said:


> Thanks for your advice. Do you have issues in your workshop with rusting tools?


I use Liberon wax on the cast iron beds of some of the machines, but other tools are in drawers and cupboards and seem not to mind, but this is a draft'y barn and I think most of the moisture is blown out the gaps under the doors, its also two stories high so any moisture in the atmosphere probably ends up above and goes out through the roof membrane under the tiles, to be honest I would not bother to try and solve a problem you don't know you have yet.


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## MARK.B. (9 Aug 2022)

Adam W. said:


> Don't, we've all been there at some point.


Some people would say that i have never got past that point


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## Jonm (9 Aug 2022)

I have only scanned through this. Looking at the roof and general construction, it looks like a lot of work and cost to get the structure thermally insulated, plus there are lots of issues with damp. I cannot see the point of thermally insulating the floor if the rest of the structure is not being insulated, all it will do is reduce airflow around the timber in the floor.

Personally I would just put in a timber floor, say 4x2 joists with brick/tile supports from the floor and dpm between joists and supports. I would want plenty of air circulation so leave a gap of say 30mm minimum between floor and wall, minimum 50 mm gap between floor and joists. Lots of preservative on the joists. Probably a dpm over the joists to keep the moisture out of the flooring. Flooring grade chipboard is fairly resistant to moisture so would probably be ok. I would put in some liftable traps so the joists can be inspected/spray treated. Screw the floor down with non rusting screws and do not glue the flooring down or together. Then the floor can be lifted to replace/repair joists if they rot. I am sure someone on here could advise on the timber to use for the joists.

Idea of prices, today I priced a small quantity of flooring, floorboards 145x20 £5.45 per m, 22mm chipboard flooring 1.2m by 2.4m £23 each, both incl vat.

If you do want a fully insulated workshop with heating then I think you need a fully costed design with tanking of walls and floor. That would destroy the character of the barn interior and I suspect the costs would be high.

As others have said, working guttering.

Some more photos, particularly outside would help.


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## Jameshow (9 Aug 2022)

If you are only there for a limited time. ...

Make it removable and you have the basis of a workshop minus the cladding and roofing sheets.


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## MCTWoodwork (10 Aug 2022)

Adam W. said:


> Rust.
> 
> I have a small stone shed with a thatched roof, it's good for the mower and mixer, but rubbish for woodworking tools.
> 
> ...


I can see why you produce excellent woodwork and carvings Adam living in a period property, loads of inspiration! You must be living the dream!


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## johna.clements (10 Aug 2022)

David66 said:


> Ah, OK.
> 
> TBH, digging out the back wall would be tricky. The main access track is right behind the shed, and about 4' higher than the floor of the shed. On the other side of the track there's rock. I suspect that digging out the wall would mean repositioning the track, which would mean digging out all the rock. And getting a digger in there (4km along a very narrow and steep 4x4 track) wouldn't be cheap!


I would not be surprised if the rock continues under the track to the barn. It could well be that the stones in the barn wall are just facework to the rock. That could explain where the boulder comes from.

I would be tempted to hand dig one or two trial holes against the wall of the barn up to 500mm deep. 

Some pictures would be good.


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## Jonm (10 Aug 2022)

johna.clements said:


> Some pictures would be good.


Agreed, we are trying to help but with very limited information.


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## Ollie78 (10 Aug 2022)

My workshop is inside a barn, though a more modern one made of blockwork and tin with a cement board roof.

The previous tennant had basically built an insulated workshop inside the exterior structure levelled the floor on large joists then studwork, celotex, osb quite a lot of windows. 
Recently I extended this with 2 rooms upstairs, I made my bit with sort of home made sips panels 11mm osb, 45*95 frame with 100mm rockwool, 11mm osb. 
I chucked 160mm of rockwool on the top and it works well. 
Max temp in the outer barn 42.8 C max inside the structure 29 C so not bad. 

I would suggest adding a breathable membrane if worried about damp but in my case the roof is good and there is air circulation around the outside so I didn`t bother with it.
Just sort of ignore the outer building and build one inside it.

Ollie


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## David66 (10 Aug 2022)

Jonm said:


> Agreed, we are trying to help but with very limited information.


Visiting this weekend. Will take more pictures


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## David66 (14 Aug 2022)

Some more pictures of the shed.

The front. 






The back. As you can see, the ground level at the back, is higher than the floor of the shed. There was a discussion about digging a trench. it's hard to see with the ferns and all, but there are huge rocks up against the back wall, which would make digging the trench manually very hard, and getting a machine there very expensive. 










This is stepping inside the door in the first picture, looking left. Generator, fire wood rack, temporary work bench. I don't plan to floor or wall this area.






This is in the same spot, looking right. This is the area I'm thinking about flooring and walling to create a work shop. It's hard to see but all the light comes in through translucent panels in the roof.






As you can see, the walls are not straight! Both the back wall and the front wall have "bulges".






The back wall is damp - not running with water, but the earth on the floor is damp.






The floor is rough cobbles and flagstones. It falls around 18" from the back wall to the front wall.






There is another "room" at the far end of the shed, through a doorway. I dont plan to do anything with this room.










So, that's it. Does this make any difference to the advice and thoughts above?


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## Jonm (15 Aug 2022)

That is quite some building, very interesting. Good photos. Filter drain outside looks a major undertaking and may not be possible if the rear wall is stone cladding to a rock face.

I see there are no gutters on the rear roof, normally I would suggest fitting gutters but there appears to be a whole hillside sloping towards this building so perhaps gutters would have minimal effect.

I think it depends how much money/time you want to spend. One way is as I suggested before, timber floor with air gap underneath and around the edges. Here is link to previous comment


Jonm said:


> Personally I would just put in a timber floor, say 4x2 joists


Here is a link to the trada tables which give joist spans for different timber sizes, joist spacing, loading and timber grade
Free UK Span Tables for Floor Joists, Ceiling Joists, Flat Roof Joists, Rafters, Purlins - Timber Beam Calculator personally I would go for smaller timber size and more supports. For shelving you could buy some stand alone shelving. If there is a howling gale through there it may need a stud wall faced with something moisture resistant, not ordinary plasterboard,

You mentioned heated workshop with wood burner. In that case it is insulated floor with insulated stud walls set away from the stone walls so air can circulate under the floor and up the gap between stone walls and stud walls and out the top. Then we get to the ceiling, you could take the studding up to the rafters then fit pir insulation to the underside of the rafters, ensuring that air can circulate between the rafters. Problem is the translucent sheet roof lights. No point in spending a lot of money on pir insulation and let loads of heat out of those. You could board over them with pir insulation or put some form of secondary glazing, maybe get some double glazed panels made and fit them in a simple frame. Or get some double glazed panels out of some second hand windows. You could always do a heating calculation and see what the heat loss would be without doing anything to the roof lights.


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## David66 (15 Aug 2022)

Jonm said:


> That is quite some building, very interesting. Good photos. Filter drain outside looks a major undertaking and may not be possible if the rear wall is stone cladding to a rock face.
> 
> I see there are no gutters on the rear roof, normally I would suggest fitting gutters but there appears to be a whole hillside sloping towards this building so perhaps gutters would have minimal effect.
> 
> ...


Thanks Jonm. Appreciate you taking the time.

The decision really does seem to be to insulate or not to insulate. My concern is that, if I dont, there will be 3-4 months of the year that the workshop will just be too cold to work in. 

Couple of questions - you say to fit PIR insulation to the underside of the rafters. How would you attach it? I had thought of nailing/screwing relative thin OSB to the underside of the rafters, and putting the PIR between the rafters, resting on the OSB.

On the roofing lights, what about something like this 









Axiome Opal 16mm Multiwall Polycarbonate Sheet


Axiome Opal 16mm glazing sheets provide a lightweight and robust solution that are used in various roofing and glazing applications. Axiome Opal colour naturally reflects heat so you can avoid heat build up. The structured layers of Axiome Opal 16mm provide greater spanning ability than the 10mm...




clearambershop.com





as secondary glazing? Looks cheaper and easier to fit than a double glazing unit.


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## Jonm (15 Aug 2022)

Putting the pir between the rafters is time consuming, you have to cut the pir with a saw to the correct width and push it in place making sure sure are no gaps next to the rafter, foam any gaps. It is time consuming and there is a lot of waste. If you cut it correctly you bash it in place and it stays there, if not diagonal screws in to rafter and seal with foam. Then you seal over the joint/timber with aluminium tape. you then have cold spots where the joists are. Modern approach is to put pir between the joists and a second pir say 50mm under the rafters. The only reason to do it is to minimise reduction in headroom but this is not an issue for you.

Putting the pir under the rafters would be much quicker, would eliminate cold spots at joist positions, cheaper as less wastage and allow air to circulate between the rafters. Fixing is simple, used these washers and long screws, then aluminium tape on the joints.





Buy TIMco MID35 Metal Insulation Disc Washers 35mm


Large diameter disc insulation washers, for use with screws to hold insulation materials to battens. They can also be used for cracked ceiling repairs. These insulation washers have a 5.0mm diameter hole in the centre. They do not come supplied with screws, meaning you can use the desired length...




www.tcfixings.co.uk





As for overboarding, do you need that, you will have a surface which reflects light, why cover it over. If you overboard then long screws, 125mm and 150 plasterboard screws are available.








Drywall Screws 125mm & 150mm Long Fine Thread Sharp Point Zinc


Fine Thread Drywall Screws to fix plasterboard to wooden studding. Zinc. Lengths 125mm &150mm 1 Bit per box. Buy Fine Thread Drywall Screws from Efixings.com




www.efixings.com





That polycarbonate sheet looks fine as long as it lets enough light through.

I will look out some photos of insulating between rafters that I did and post them


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## Jameshow (15 Aug 2022)

David66 said:


> Thanks Jonm. Appreciate you taking the time.
> 
> The decision really does seem to be to insulate or not to insulate. My concern is that, if I dont, there will be 3-4 months of the year that the workshop will just be too cold to work in.
> 
> ...



0r a 2x1 frame with two sheets of polythene bags either side DX bags for instance.


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## johna.clements (15 Aug 2022)

The main sources of water are, off the roof because there are no gutters, surface water and water running through the ground.

In the second picture the track appears to slope towards the camera. I would dig a shallow trench about 1m off the track, towards the barn, maybe 150 deep by 300 wide (shovel plus a bit). Tip the spoil on the the barn side of the trench to increase the "depth" of the trench. It will catch most of the surface water that leaves the track which could be most of the water that ends up against the barn wall. Make sure the trench does not have any ponds in it, always has a slight fall, it can wiggle a bit to get around rocks.

The ground water could be partly solved by the trench if the rock is up to the bottom of the trench and is not cracked. If the subsoil is sandy a trench could make the ground water worse, you would need to seal the bottom of the trench (maybe a thin layer of clay or concrete).

I would put on a gutter and run it to a water butt. Whilst it may not be the biggest source of water it would produce a free source of water.


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## Jonm (15 Aug 2022)

Jonm said:


> MI will look out some photos of insulating between rafters that I did and post them


This is my sons extension, I installed most of the insulation with some assistance, also did the building regs drawings and a lot of other work. This photo shows the insulation between the rafters, the sheets under the rafters, the washers and some taped joints. The void between the top of the insulation and the roofing underlay is vented at the eaves and ridge.






Just for info, here is the finished extension


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## Adam W. (15 Aug 2022)

That shed will collapse if you try to dig out the back.


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## David66 (15 Aug 2022)

Adam W. said:


> That shed will collapse if you try to dig out the back.


Dont worry, I have no intention of digging out the back. It would need way to much work to do by hand, and getting a digger in (4km along a very rough and steep 4x4 track), would be horribly expensive.


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## Adam W. (15 Aug 2022)

MCTWoodwork said:


> I can see why you produce excellent woodwork and carvings Adam living in a period property, loads of inspiration! You must be living the dream!


It's a crumbly dream and some may even describe it as a bit of a nightmare, but we've saved it from demolition and I'm happy with that. It's lovely and cool in the heat, which is nice as I melt easily.


David66 said:


> Dont worry, I have no intention of digging out the back. It would need way to much work to do by hand, and getting a digger in (4km along a very rough and steep 4x4 track), would be horribly expensive.


 That's saved you some work then.


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## 1steven (15 Aug 2022)

Is that cement as mortar or lime?


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## mikej460 (15 Aug 2022)

So digging the back is out, but I totally agree that guttering is a must. After that it's what I said earlier, I would construct a raised floor and insulate the roof. If, after this, the barn is still damp then build the inner walls using battens, studs and housewrap.


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## Fitzroy (16 Aug 2022)

My 2p worth, which I think is what others have suggested (I think your original idea) is to build a building within the building isolated from the structure. I think you are on a loosing battle trying to remedy the damp issue, gutters would help but at what cost and to what level of benefit. You'd loose the lovely aesthetics but the only way to keep those would be a full on renovation £££££, which seems a poor choice as it is not your building you are investing into.

One of the positives of building a structure inside is that you have a good weather screen so you're not really worried about managing water ingress from rain etc. So for example you could look out for a large second-hand double glazed window (free on gumtree) and use it as a skylight facing the transparent roof panel.

You would loose some space internally as I think you would want to leave a good gap at the rear between the damp wall and the new structure, so that the old wall still has reasonable ventilation to/from the roof void. With a 100mm gap and a 100mm stud wall at rear and a 50mmg gap and 100stud wall at front, you've just lost 350mm from the width of the room, is that manageable?

Messing about in sketch-up, some of the things that jump out at me are:
- is the space big enough to enter through the normal door and then have another door on the internal structure.
- do you need access internally to the doorway to the room on the right, it looks like there is another door, so perhaps not.
- you risk creating a fantastic home for wildlife, under or between the internal walls, i was warned of this when I put insulation quilt in the floor of my shed, fingers crossed so far i've been ok, but im urban not rural.
- if you uses screws for construction, you can dismantle and take with you, some cladding on the outside and you have a shed.
- a 4x2 floor with lots of feet to limit span width and hence timber height, dpm under the 'feet' to stop damp ingress into the timbers.
- I would cross batten the internal roof structure for insulation and space for a reclaimed window
- simple 4x2 frame with PIR insulation in floor, walls, and ceiling. Internally clad in your choice, 9mm ply or 11mm osb
- i'd not bother with external building wrap as there should be no water to worry about
- with this approach the cold side of the isulation is very well ventilated to no worry about condensation either
- you may want a couple of LED panels in there the design would reduce the incoming light from the panel
- i think you're looking at c.£2k for materials

Some thoughts, perhaps helpful perhaps not.


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## johna.clements (16 Aug 2022)

I know the op suggested 4x2 feet to sit the floor on but I think it would be better to use engineering bricks, slate/ quarry tiles. 

The existing floor is very uneven with the channels for animal product etc. Square cut 4x2 will in many cases only be resting on an edge or corner. In some cases they could end up in low points so some dpm will not do much good. They will all be different sizes.

If you use engineering bricks, slate/ quarry tiles you can take out all the variation with the mortar under the brick or tiles (depending if it is a high or low spot.) Then put a bit of dpm over each pad and build away off a level surface or a couple of level surfaces to take account of the barn cross fall.


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## David66 (16 Aug 2022)

1steven said:


> Is that cement as mortar or lime?


mortar


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## David66 (16 Aug 2022)

Fitzroy said:


> My 2p worth, which I think is what others have suggested (I think your original idea) is to build a building within the building isolated from the structure. I think you are on a loosing battle trying to remedy the damp issue, gutters would help but at what cost and to what level of benefit. You'd loose the lovely aesthetics but the only way to keep those would be a full on renovation £££££, which seems a poor choice as it is not your building you are investing into.
> 
> One of the positives of building a structure inside is that you have a good weather screen so you're not really worried about managing water ingress from rain etc. So for example you could look out for a large second-hand double glazed window (free on gumtree) and use it as a skylight facing the transparent roof panel.
> 
> ...


Thanks so much for your input.The width of the building internally is about 3.7m, and around 5m in length - so losing 350mm is probably fine.

I think there is room for an internal door - however, I do need internal access to the far room. So there will need to be 2 doors. 

£2k in materials "yikes" ..... !


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## David66 (16 Aug 2022)

Thank you all for your advice. Much appreciated.

Looks like I need to make a decision on whether to insulate or not. If not, then a simple raised floor, and maybe a wall to hang stuff on would probably be fine.

Trouble is, there will be 3-4 months of the year where it will be too cold to work in the shed. Also, there may be rust issues with the tools.

If I insulate (and heat) the shed - then an internal room is probably necessary. It would be much more expensive (at least double the cost) more work, and more complexity.

TBH - I dont mind the work and the complexity ... think I might actually enjoy it ... but the cost is an issue - and ... it's gonna look a bit odd!

Decisions decisions


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## johna.clements (16 Aug 2022)

£2k seemed quite cheap to me. 

But since the workshop will be inside and not subject to the wind and snow could the walls and roof use smaller timbers than 2 by 4? Will you need to get on the top of the workshop.

I have seen many offices in box type constructions inside factories and warehouses, nothing odd.


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## David66 (16 Aug 2022)

johna.clements said:


> £2k seemed quite cheap to me.
> 
> But since the workshop will be inside and not subject to the wind and snow could the walls and roof use smaller timbers than 2 by 4? Will you need to get on the top of the workshop.
> 
> I have seen many offices in box type constructions inside factories and warehouses, nothing odd.


Good point - no need to get on top of the box - so would 2x2 for the wall framing work?

Where would the bulk of the costs be - in the wood?


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## Jameshow (16 Aug 2022)

David66 said:


> Thanks so much for your input.The width of the building internally is about 3.7m, and around 5m in length - so losing 350mm is probably fine.
> 
> I think there is room for an internal door - however, I do need internal access to the far room. So there will need to be 2 doors.
> 
> £2k in materials "yikes" ..... !


I'd make the inner room 3.6m X 2.4m if at all possible. 

50mm cavity will be fine. 

3x2 will be fine ( and better if you want to use later on) with a 50mm pir / polystyrene insulation building fabric to outside and osb to inside.


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## David66 (16 Aug 2022)

Jameshow said:


> I'd make the inner room 3.6m X 2.4m if at all possible.
> 
> 50mm cavity will be fine.
> 
> 3x2 will be fine ( and better if you want to use later on) with a 50mm pir / polystyrene insulation building fabric to outside and osb to inside.


Why 3.6m by 2.4m that's a lot smaller than nit could be.


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## johna.clements (16 Aug 2022)

David66 said:


> Good point - no need to get on top of the box - so would 2x2 for the wall framing work?
> 
> Where would the bulk of the costs be - in the wood?


I was thinking 4 x2 for framing around doors, corners, windows, where you are going to hang shelves, roof plate and 4 by 1.5 other places in roof and walls.


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## Fitzroy (16 Aug 2022)

David66 said:


> Thanks so much for your input.The width of the building internally is about 3.7m, and around 5m in length - so losing 350mm is probably fine.
> 
> I think there is room for an internal door - however, I do need internal access to the far room. So there will need to be 2 doors.
> 
> £2k in materials "yikes" ..... !


I estimated about 70m2 of wall, floor and ceiling area. At £40 per 100mm insulation board that £900 of insulation. About £600 for osb and £500 for studs, fixings etc. 

You can often see cheap insulation on gumtree etc folks with a board left over after a job. you’ve plenty of space to store it so you could bring that price down with some patience, what your building is never going to be building regs compliant so any old seconds or partial damaged bits would work.


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## Jameshow (16 Aug 2022)

johna.clements said:


> I was thinking 4 x2 for framing around doors, corners, windows, where you are going to hang shelves, roof plate and 4 by 1.5 other places in roof and walls.


Just be aware 4x2 is larger than 4x1.5 

95x 45 Vs 89 X 36....


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## Jameshow (16 Aug 2022)

David66 said:


> Why 3.6m by 2.4m that's a lot smaller than nit could be.


Sorry I meant 3.6 wide X however long and 2.4 high if possible!


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## Adam W. (16 Aug 2022)

Having looked at the pictures, I still stand by my suggestion of getting a wooden shed and not bothering with the stone barn.


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## David66 (17 Aug 2022)

Jameshow said:


> Sorry I meant 3.6 wide X however long and 2.4 high if possible!


Ah... that makes sense. I think I can make it 3.6m wide, and 4.8 long. 2.4 high won't work though. In the words of the late great Meatloaf "2 out of 3 aint bad"!!


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## David66 (17 Aug 2022)

Reviewing all the comments there is one thing that I wanted to ask.

Some recommend a double wall, with building wrap on the outside wall, then an internal, insulated wall. Others have said that a single insulate wall would be OK, providing there is a 100mm gap to the rear wall. No need for the building wrap.

What's the thinking behind the double wall method, and what is the advantage/disadvantage (double wall is obviously more expensive)?


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## Fitzroy (17 Aug 2022)

My understanding of the whole wall construction conundrum. A workshop wall typically needs to provide two functions, a protection from the weather and insulation to the building. You also have a couple of issues to consider, first how you actually construct the wall so it stays standing and is weathertight before the building is finished, and secondly you need to manage the risk of condensation. With these in mind:

Protection from the weather and the risk of moisture penetration is managed by having a two layer design. An outer layer that should prevent ingress, often cladding on a shed, and an inner layer that any penetrating moisture can drain down to a suitable location. Using building wrap on a shed means that any penetrating moisture is stopped by the membrane from reaching the main structure.

When insulating a building you end up with a warm side and a cold side. The air on the warm side will hold more moisture than on the cold side, so any moist air that moves from warm to cold will drop out condensation. If this condensation occurs in the wall you can get interstitial condensation which leads to damp. This is managed in two ways, normally with a vapor barrier on the warm side between the insulation and the final wall facing, and then providing a ventilated area on the cold side of the wall so that any condensation that does occur can evaporate/dissipate over time.

Building a stud wall and putting osb on the outside of the wall means that you very quickly have a fairly weather proof structure. Additionally it allows you to come back and insulate at a later date from the inside, in dry conditions, which is nice from a construction view point. However, once you come back and insulate you have the risk of interstitial condensation behind the insulation on the interior surface of the external board, which is unvented. Building this way is common practice in some parts of USA and Canada, take from that what you will.

Building with building membrane on the outside, then insulation, then internal boards is beneficial from a cost perspective as it minimises the amount of materials, and is ensures a well ventilated and breathable 'cold-side'. However, until the external cladding/rain screen is in place it leaves the building a bit exposed to damage, as the membrane can be wind damaged and rain can pass into the already installed insulation. Additionally from a wall strength/stability viewpoint you want to get the internal boarding done asap. I'd also say you would be limited to solid types of insulation board rather than any kind of quilt.

Building an internal structure as you have proposed. You do not need to worry about penetrating moisture as the existing building provides all the protection you need from rain etc, and the large gap with no connection to the external walls mean anything that does penetrate will run down the internal surface of the existing walls to the floor. You have less worry over immediate structural strength as again the existing building gives you protection from wind etc. So IMHO you have no need for building wrap nor external boarding, and by going that route you open up the possibility of interstitial condensation.

Sorry essay, but i'm keen to put my thinking out there so others can educate me as every day is a school day.

Fitz.


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## johna.clements (17 Aug 2022)

I assume that the workshop will only be heated whilst in use. 
The barn roof looks fairly new so little wind and rain would get in to wet the exterior but there would be no sun and wind to dry it.

I have never used one but would a small solar powered extractor fan lower the moisture level inside the workshop to the general barn level. I know it would not run for long on rainy days in January.

@Fitzroy what are your thoughts on a moisture barrier under the inner boarding.

Not sure what the workshop will be used for but if less mositure gets into the workshop there will be less condensation. I would hang wet coats and boots outside.


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## Fitzroy (17 Aug 2022)

I think for a workshop that is in occasional use the whole condensation thing is very unlikely to be an issue whatever you do. If you're building say a garden room that's going to be an office for multiple people 8hrs a day, or is going to host yoga classes with 15 sweaty folks, then I think you may want belt and braces and an internal moisture barrier, otherwise OSB or Ply will be sufficient.

BTW these are my opinions after lots of googling, combined with being a chemical engineer by profession, so I understand the theory of heat and mass transfer. They are not based on years of practical application in building construction.

Potentially just educated enough to be dangerous.


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## Ttrees (17 Aug 2022)

Adam W. said:


> That shed will collapse if you try to dig out the back.


So what's the issue here?
Presumably there's plenty of stone to be found under the soil.
Could have another shed with the leftovers.
My shed is a bit drier from doing the same kinda thing.





I don't know anything whatsoever about building, but seems to me a timber shed in a wet stone shed would rot, and besides who wants a suspended floor compared to concrete or whatever.

Can this building be raised whilst you're at it, getting the floor higher than the ground
That would presumably be easier to put a level floor and membrane in and simplify other stuff like doors ect.

Having had a brief look at building an insulated shed from stone,
it seems this is not a done thing.
I guess you folks in the UK do it though, as you folks have older buildings than we do.

Best info I've came across would be stone cladding,
as I've thought about using stone I have for a wee potting/garden shed.
I was toying with the idea of making a block wall inside,
and stone course on the outside (not cladding/stone on edge)

Sorry if I'm derailing the topic, just figured posting this if it may be a consideration?


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## johna.clements (17 Aug 2022)

Fitzroy said:


> I think for a workshop that is in occasional use the whole condensation thing is very unlikely to be an issue whatever you do. If you're building say a garden room that's going to be an office for multiple people 8hrs a day, or is going to host yoga classes with 15 sweaty folks, then I think you may want belt and braces and an internal moisture barrier, otherwise OSB or Ply will be sufficient.
> 
> BTW these are my opinions after lots of googling, combined with being a chemical engineer by profession, so I understand the theory of heat and mass transfer. They are not based on years of practical application in building construction.
> 
> Potentially just educated enough to be dangerous.



I am a civil engineer by profession. Only built two buildings, steel frames on rc base in a power station. When I was at technical college around 1980 we studied where interstitial condensation would occur, calculated U values etc. But that was a long time ago and have not looked at my text book that covers that in awhile.


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## johna.clements (17 Aug 2022)

Ttrees said:


> So what's the issue here?
> Presumably there's plenty of stone to be found under the soil.
> Could have another shed with the leftovers.
> My shed is a bit drier from doing the same kinda thing.
> ...


The barn is owned by someone else so there is a limit to what he can do.

Not sure why the timber in a room inside the barn should rot more than any other timber in the barn. That is assuming it is not in contact with the wet stone wall and floor.


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## Ttrees (17 Aug 2022)

Apologies, I missed that bit, seems a possibly expensive thing to be trying for something not ones own building, but needs must.

Regarding the rotting concerns I made in the seemingly damp shed, I'm guessing so from the green stone on page 3 
Perhaps it was taken into the house for some reason or another, I didn't look that closely at the rest.

I'd guess one would need vents everywhere if it were damp, for that solution to work?


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## johna.clements (17 Aug 2022)

Ttrees said:


> Apologies, I missed that bit, seems a possibly expensive thing to be trying for something not ones own building, but needs must.
> 
> Regarding the rotting concerns I made in the seemingly damp shed, I'm guessing so from the green stone on page 3
> Perhaps it was taken into the house for some reason or another, I didn't look that closely at the rest.
> ...



A room in the barn seems to have less of a damp problem than your shed. 

Putting a room inside the barn has a number of advantages and disadvantages.

The foundations are already there, all you need is to level at a number of points under the joists.

The barn will keep the wind, rain and snow off the room. A separate structure would require more insulation to keep it as warm. It would have to be more substantial to resist the wind and snow. 

Work can be undertaken at your leisure since it is inside (and in an out building so no one else! to complain).

Artificial lighting will be required at all times.

Restrictions on the size.

I am sure there are more both ways.


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## Jonm (18 Aug 2022)

David66 said:


> Reviewing all the comments there is one thing that I wanted to ask.
> 
> Some recommend a double wall, with building wrap on the outside wall, then an internal, insulated wall. Others have said that a single insulate wall would be OK, providing there is a 100mm gap to the rear wall. No need for the building wrap.
> 
> What's the thinking behind the double wall method, and what is the advantage/disadvantage (double wall is obviously more expensive)?


I am not sure what the “double wall” solution is. Would need to see a sketch to understand what is proposed. Personally I would not try to put a membrane against the existing wall, it will just trap the moisture and loads of mould behind it.

if you go for pir insulation, I would cut it down the middle so it is 600 mm wide then fit stud, insulation then stud, ie fix the stud to fit the pir. If it needs overboarding put the 2,4 metre length horizontal to minimise wastage. This would minimise wastage of pir which is the expensive stuff.


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## David66 (26 Aug 2022)

I think I've pretty much decided to go with the insulated option.

Question about insulating the floor. Rather than insulating between the floor joist, could I just lay the PIR sheets on top of the floor joists, and then frame around them, before laying 18mm OSB on top. Would the PIR have sufficient structural integrity to support the OSB floor between the (say) 2x2 framing, given they would be at 1.2m gaps across the width of the PIR boards? 

I'm trying to save the work/waste of cutting the PIR boards and laying them between the floor joists. 

Also, starting to price up the materials. 50mm polystyrene sheets are half the price of PIR boards. Would they work just as well?


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## rogxwhit (26 Aug 2022)

David66 said:


> 50mm polystyrene sheets are half the price of PIR boards. Would they work just as well?


No! You get what you pay for, in effect. So it depends what you want. I'm not keen on any insulation being load-bearing under the floor.


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## johna.clements (26 Aug 2022)

Many chemicals dissolve polystyrene.

Polystyrene is not good in a fire.


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## David66 (26 Aug 2022)

rogxwhit said:


> No! You get what you pay for, in effect. So it depends what you want. I'm not keen on any insulation being load-bearing under the floor.


Thanks - what are the trade offs for polystyrene versus PIR?


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## Jonm (26 Aug 2022)

David66 said:


> I think I've pretty much decided to go with the insulated option.
> 
> Question about insulating the floor. Rather than insulating between the floor joist, could I just lay the PIR sheets on top of the floor joists, and then frame around them, before laying 18mm OSB on top. Would the PIR have sufficient structural integrity to support the OSB floor between the (say) 2x2 framing, given they would be at 1.2m gaps across the width of the PIR boards?
> 
> ...


Not quite sure what you are proposing with talk of framing.

With concrete ground floors it is now standard procedure to lay 100 PIR on the prepared base then 100 concrete on top. In these circumstances the pir is supported underneath across its whole area and loads from above are distributed by the concrete slab.

With your proposal the loads will be taken by the pir immediately above the joists. I can see that over time the pir may disintegrate/compress, depending on usage and weight of equipment. I would not take the risk as remedial works would be difficult.

You mention OSB flooring, reasonably ok for a cheap lightly used garden shed but not for a workshop. I would use flooring grade T&G chipboard. This is completely different to the ordinary chipboard and is resistant to moisture, I have used pieces outside unprotected lying on the ground, it did not swell and blow apart. Different thicknesses and types available, some has a sacraficial cover for new construction, it is fitted soon after placing the joists and then used as a working platform for the remainder of the build, open to the weathers, the covering is then removed, it is there to stop mortar/plaster mud from sticking to the flooring. Modern construction method is to glue it to the joists and glue the joints together then pin it down, prevents squeaks and makes the floor very solid. Absolute pain if it needs to be lifted.

Cutting the pir is fairly easy with a handsaw. Main thing is a tight fit between the joists, some long diagonal screws to stop it dropping or better to put timber strips fixed to the joists to support the pir from underneath, would not be good if it fell down, foam any gaps between joist and pir. I would use good quality foam, my foam gun clogged up when I used cheap foam.

Here is a picture of my first floor during the build, it shows what a hammering the floor took, when the covering was peeled off it looked fine. Not suggesting you need the board with the sacrificial covering. This floor also stood up to the “beast from the east”.


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## rogxwhit (26 Aug 2022)

David66 said:


> Thanks - what are the trade offs for polystyrene versus PIR?


The styrene only has a bit more than half the insulation value for the same thickness.


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## David66 (26 Aug 2022)

"Not quite sure what you are proposing with talk of framing."

Sorry - I'm still getting used to the language! What I had in mind is laying the floor joists, and then laying full PIR sheets on top of the joists, and at right angles to them. By framing I meant I would then attach 2x2 lengths to the joists, at the long edge of each PIR board "framing" them in, laying the OSB on top of that. 

From what you say though, this wouldn't work as it would put too much pressure on the PIR, which would degrade over time.


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## Jameshow (26 Aug 2022)

I'd make it in sections say 12x 6 which can be removed if and when you want to move out.


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## johna.clements (26 Aug 2022)

David66 said:


> "Not quite sure what you are proposing with talk of framing."
> 
> Sorry - I'm still getting used to the language! What I had in mind is laying the floor joists, and then laying full PIR sheets on top of the joists, and at right angles to them. By framing I meant I would then attach 2x2 lengths to the joists, at the long edge of each PIR board "framing" them in, laying the OSB on top of that.
> 
> From what you say though, this wouldn't work as it would put too much pressure on the PIR, which would degrade over time.


The OSB will not span 1200 between the 2x2 and so will load the PIR sheet. The PIR sheet will only be supported locally at the joists and so will crush over time.


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## Jonm (26 Aug 2022)

David66 said:


> 50mm polystyrene sheets are half the price of PIR boards


Have you taken in to account the difference in thermal conductivity? To replace 50 of pir you would need over 80mm of polystyrene.


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## David66 (26 Aug 2022)

Jonm said:


> Have you taken in to account the difference in thermal conductivity? To replace 50 of pir you would need over 80mm of polystyrene.
> View attachment 142372


Thanks - it kinda begs the question - what u value should I be looking to achieve on the walls/floor/roof?


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## rogxwhit (26 Aug 2022)

Remind me what the proposed heating regime is meant to be, a quick scroll through isn't giving me the reference. Think I saw woodstove mentioned briefly? Maybe I should've said heating regime and occupancy pattern. These provide the context for the insulation requirement.


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## David66 (26 Aug 2022)

rogxwhit said:


> Remind me what the proposed heating regime is meant to be, a quick scroll through isn't giving me the reference. Think I saw woodstove mentioned briefly? Maybe I should've said heating regime and occupancy pattern. These provide the context for the insulation requirement.


Basically it's an old stone built barn, in which I'm going to be building a raised floor and lining the walls. As for heating, probably a wood burner. I'll be in there maybe a couple of hours every other night, and hopefully longer at the weekend. Just me.

Oh, and it's in the north of Scotland - gets pretty cold!!


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## Jonm (26 Aug 2022)

rogxwhit said:


> Remind me what the proposed heating regime is meant to be, a quick scroll through isn't giving me the reference. Think I saw woodstove mentioned briefly? Maybe I should've said heating regime and occupancy pattern. These provide the context for the insulation requirement.


Spot on, David66 needs to tell us what temperature he wants and how long for during the winter months. Also what the average external temperatures are and does he want the heating to be effective when it is bitterly cold, say -5degC outside. It can be very cold in Scotland. Also heating method and size of this box he is building.


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## rogxwhit (26 Aug 2022)

That'll be intermittent heat then. Which is bad news for tools and rust, because every time the air cools there'll be condensation on steel surfaces. 

Sounds as if a modest amount of insulation would suit, though. What might the periods of occupancy be, and what type of activity is likely?


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## David66 (26 Aug 2022)

Jonm said:


> Spot on, David66 needs to tell us what temperature he wants and how long for during the winter months. Also what the average external temperatures are and does he want the heating to be effective when it is bitterly cold, say -5degC outside. It can be very cold in Scotland. Also heating method and size of this box he is building.


Happy to wear a jumper, so mid teens centigrade. Would need heating to get there from October to March say. Average temps are between 8C and 6C during this period. If it's less than -5C - I'll probably not bother! Box will be around 3.6m by 5m, by 2.5m high.


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## Jonm (26 Aug 2022)

David66 said:


> Happy to wear a jumper, so mid teens centigrade. Would need heating to get there from October to March say. Average temps are between 8C and 6C during this period. If it's less than -5C - I'll probably not bother! Box will be around 3.6m by 5m, by 2.5m high.


Ok, I will try and do a calculation later, unless someone else jumps in and does it. Need to get on with some jobs around the house.


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## rogxwhit (26 Aug 2022)

As a baseline, how about 50mm insulation in walls & ceilings ... forget the floor.

I think you need to concentrate on structure (especially that of the floor), and following that it seems that walls & roof only need a single skin internally with the insulation outboard of that.

Unfortunately for any form of glazing there's an added insulation / cost equation. :-(


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## Jonm (27 Aug 2022)

Jonm said:


> I will try and do a calculation later


Had a quick look at this, used the celotex online calculator for u values. It is a bit limited, not allow zero insulation thickness Etc. U values are W/m2K

*Floor*, insulation between joists, only allows for 400 joist spacing, standard floor board thickness
20 celotex 0.55
50 celotex 0.37
75 celotex 0.29
100 celotex 0.24

*Ceiling*, insulation between joists, 600 rafter spacing, 12.5mm plasterboard thickness
20 celotex 0.89
50 celotex 0.46
75 celotex 0.34
100 celotex 0.27

Could use ceiling values for wall. Not sure why it is giving such a big difference for the 20 mm celotex in floor and ceiling. 

This is a start, I will send some calcs later to give heating requirements.


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## rogxwhit (27 Aug 2022)

Jonm said:


> Not sure why it is giving such a big difference for the 20 mm celotex in floor and ceiling.


I assume that it factors in location and that in a given space there'll be convection currents. The temperature will tend to be higher at the ceiling than at the floor, so there'll be a steeper temperature gradient through the envelope, thus faster heat loss? That's just my primitive take on it & I'm open to correction.


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## rogxwhit (27 Aug 2022)

It would be good if natural light could be 'imported' - apart from the qualities it can have as a work light, it also has psychological benefits ...


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## David66 (27 Aug 2022)

Jonm said:


> Had a quick look at this, used the celotex online calculator for u values. It is a bit limited, not allow zero insulation thickness Etc. U values are W/m2K
> 
> *Floor*, insulation between joists, only allows for 400 joist spacing, standard floor board thickness
> 20 celotex 0.55
> ...


Thanks Jon - really appreciate the thought going into this.


rogxwhit said:


> It would be good if natural light could be 'imported' - apart from the qualities it can have as a work light, it also has psychological benefits ...


There are 2 large translucent panels in the roof, which let in a bunch of light. I plan to insert similar panels into the inner roof so that the light comes through.


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## Jones (27 Aug 2022)

The floor/ceiling values are different as heat rises. Insulation will only keep heat in if you actually add heat ,if you are reluctant to pay for that then a bit of insulation won't make much difference to the temperature inside. Regarding insulating the floor expanded polystyrene will be cheaper and for an occasional and temporary workshop should be adequate.


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## Jonm (27 Aug 2022)

David66 said:


> Thanks Jon - really appreciate the thought going into this.
> 
> There are 2 large translucent panels in the roof, which let in a bunch of light. I plan to insert similar panels into the inner roof so that the light comes through.


Here are some calcs, they are more for sizing a radiator than working out cost of heating. For example I have assumed outside temperature of 0C wheras it will generally be 6C. Air changes is another area.. Another point is heat required to get the workshop and it’s contents up to temperature, 

I cannot post the excel spreadsheet but can send it to you if you wish. If there are any mistakes in it someone on here will spot it. Calcs are for 50mm celotex.


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## Jonm (28 Aug 2022)

rogxwhit said:


> I assume that it factors in location and that in a given space there'll be convection currents. The temperature will tend to be higher at the ceiling than at the floor, so there'll be a steeper temperature gradient through the envelope, thus faster heat loss? That's just my primitive take on it & I'm open to correction.


The floor calc assumes timber floors wheras the ceiling assumes plasterboard so that is one difference. As you say there is a temperature gradient in the room and generally the temperature is higher near the ceiling so maybe the calcs are taking this in to account.

My concern was that generally the ceiling values are about 25% more than the floor but for the 20mm insulation they are 60% more. I went back and checked the results as I thought I had made a mistake, on the basis if something looks wrong it probably is.


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## David66 (28 Aug 2022)

Thanks guys - appreciate this.

I'm still looking at cheaper alternatives to PIR boards. Came across thermal fleece and rock wool. For floors you install it on top of plastic netting, on which it sits. That would work for the ceiling too - but how would you attach it to the stud work on the walls, so that it doesn't just collapse before/after you put on the OSB sheeting?


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## Adam W. (28 Aug 2022)

Ttrees said:


> So what's the issue here?
> Presumably there's plenty of stone to be found under the soil.
> Could have another shed with the leftovers.
> My shed is a bit drier from doing the same kinda thing.
> ...


A bit late to the party, but as stated a loooooong way above, it's not his shed.


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## Jonm (28 Aug 2022)

David66 said:


> Thanks guys - appreciate this.
> 
> I'm still looking at cheaper alternatives to PIR boards. Came across thermal fleece and rock wool. For floors you install it on top of plastic netting, on which it sits. That would work for the ceiling too - but how would you attach it to the stud work on the walls, so that it doesn't just collapse before/after you put on the OSB sheeting?


David, if you have not done so already I think it would help if you priced this up without any insulation, then decide what money you have to spend on insulation. You have, floor joists, floorboards, stud walls, wall surfacing, two doors, two door linings, locks, handles, hinges, roof lights, wood burning stove, flue, flashing kit through the roof, electrics, damp proof membrane etc. then add 15% for the ancillary bits like screws, foam etc.

You may find that it is too expensive without any insulation and have to rethink the project. 

As for rock wool in the walls, netting on the back to stop it falling out against the damp stone walls, should then stay in place to fit the osb. For the ceiling is there sufficient headroom to fit ceiling boards and put rock wool on top as you go, then do last bit from the main area of the barn. Pushing Rockwool up between joists from underneath then trying to keep it in place would be a horrible job, I would avoid it.


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## David66 (28 Aug 2022)

Jonm said:


> David, if you have not done so already I think it would help if you priced this up without any insulation, then decide what money you have to spend on insulation. You have, floor joists, floorboards, stud walls, wall surfacing, two doors, two door linings, locks, handles, hinges, roof lights, wood burning stove, flue, flashing kit through the roof, electrics, damp proof membrane etc. then add 15% for the ancillary bits like screws, foam etc.
> 
> You may find that it is too expensive without any insulation and have to rethink the project.
> 
> As for rock wool in the walls, netting on the back to stop it falling out against the damp stone walls, should then stay in place to fit the osb. For the ceiling is there sufficient headroom to fit ceiling boards and put rock wool on top as you go, then do last bit from the main area of the barn. Pushing Rockwool up between joists from underneath then trying to keep it in place would be a horrible job, I would avoid it.


Words of wisdom. 

I've done a rough estimate, but I need to go back to the shed to to finalise measurements as my thinking has developed. Should be able to do this in the coming week/weekend. 

I'll report back!

P.S. Yes, there should be enough room to do as you suggest in the ceiling.


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## Jameshow (28 Aug 2022)

You can get off cuts of kingspan off eBay. 

Polystyrene would be my default choice, I'd avoid rockwool at all costs from an ichy point of view. 

Sheep's wool would be better tbh.


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## mikej460 (28 Aug 2022)

With insulation there is the law of diminishing returns to consider, bear in mind that you don't want to live in this space but just comfortable to work in and reduce rust issues. I would use 60 to 100mm polystyrene in the floor (check eBay POLYSTYRENE EPS 70 INSULATION SHEETS 100MM 2400 X 1200 MULTI list 6 for £185 | eBay where I bought mine, great product and service), Knauf Earthwool in the walls and in the roof (but you need to fit 9mm OSB3 to the inside of the roof joists to stop you wearing it.


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## Jonm (28 Aug 2022)

Jameshow said:


> I'd avoid rockwool at all costs from an ichy point of view


Very true, I would use it between/over ceiling rafters when installed from the attic above, elsewhere I would avoid it. Hate installing the stuff.


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## Jones (28 Aug 2022)

For between roof joists to there are special mineral wool rolls which spring in and won't fall back out immediately , itching isn't really a problem with the decent modern stuff. Rockwool rafterline is one I've used several times and it can also be used vertically, getting hold of less than a pallet can be difficult and expensive though.


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## steve66 (29 Aug 2022)

In my case, an old cow shed, retro fitted an internal stud wall, brackets held it in place off wall, insulated with second hand insulation, double skinned osb, this was done when 9mm osb was half the price it is now. I knew someone who had the contract to replace insulation in houses so I got the insulation free ( plus the odd Xmas decorations) 
I put in suspended ceiling that allowed attic space to insulate.


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## David66 (29 Aug 2022)

Thanks Steve - when you say "double skinned OSB" do you mean there was a sheet on the outside of the stud and on the inside, with the insulation "sandwiched" between them? Why did you decide to do that?


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## steve66 (29 Aug 2022)

Same principal in building timber frame houses, modern regs in timber frame houses is 6 inch timber, but 4 inch would suffice. 
I wouldn’t be able to afford the insulation as well so I used second hand insulation to save on cost. It’s defiantly improved the building and keeps everything dry. 
I have to treat outside walls but I’ve bought machines and sundry items off carpenters who have had similar sheds without insulation and they’ve always been rusty. 
Old fiber cement corrugated roof, but I had the room to put in a suspended ceiling as well


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## steve66 (29 Aug 2022)

Part of the suspended ceiling, I’ve re-bagged insulation so not as heavy as they were, just in case any have to come down.
All sheds and buildings I’ve done have been the same, it works for me. 
Yes regards one sheet on outside of stud, insulation put in and then boarded again on inside


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## housemaintenance88 (20 Sep 2022)

Hi, you have loads of areas to work on however, if I read right and the drop from left to right is 18", blimey, may I suggest these with some concrete blocks under them to elevate to begin with and then these can adjust giving a further 0"-2" tolerance. https://www.amazon.co.uk/Galvanised...ted+post+base+post+holders,aps,54&sr=8-9&th=1
If you pencil mark the holes through the base on the blocks and then buy some "multi construction bits" to drill WITHOUT HAMMER ACTION and then rawl plug the concrete blocks. I would put freshly mixed concrete around the concrete blocks given you have a flint floor this should hold pretty well and allow you to level the blocks, if you put concrete around, under the blocks you should be able to lay the blocks even in their longest direction upwards to help with the 18" drop. This then would help keep your joist above-off the floor and hopefully stop them rotting.


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## MikeJhn (26 Sep 2022)

Just punch the floor joists off the existing floor with some timber legs under them, legs on a dense tile or brick on a mortar bed, the floor joists can have multiple supports onto the existing floor so span longitudinally is not an issue, only the distance between joists to span the flooring material, essential to have a DPC between the legs and floor and noggins between the joists, half the time and effort, establish the low side and just spirit level across the floor to the other end of the joist, measure the distance to the floor, don't think I need to go through the whole process, no disturbance to the existing floor and can be taken up easily when you move out. mine has been down for ten years without any maintenance being needed.


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## David66 (30 Sep 2022)

Update - we've moved into our new home and the shed build has begun. Couple of photos below (sorry, last two use portrait orientation, but have uploaded as landscape!).

I have all the framing done. I lost a bit of volume because the stone walls were so uneven. Ended up about 3m by 5m. I laid a DPM, as advised, and for reasons of cost, decided simply to support the joists with timber legs resting on the DPM. After a lot of trial and error (and a laser level!!), the floor is level and the the walls are square (at least as far as I can tell)!! 

Today it's insulating and laying the floor. Again, for reasons of cost I've gone with rock wool insulation rather than PIR boards. 

More updates to follow


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## Housey210 (30 Sep 2022)

Rent, you say. Be wary of any repairing clauses. I would walk away from it and put the money into a build at your own home.


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## David66 (30 Sep 2022)

Housey210 said:


> Rent, you say. Be wary of any repairing clauses. I would walk away from it and put the money into a build at your own home.


I know...it's a long story. The house is off grid, and in the middle of nowhere (4km down a 4x4 track). It's owned by a friend who's agreed to let us stay there rent free provided we finish the renovations he started about 10 years ago (!). We'll be there for about 3 years, while we build a new house (I say, build, but my involvement will be minimal!). If I didn't fit out the shed I would have no workshop for 3 years "shrug" - with the amount we're saving on energy bills (pre installed solar, wood burning stoves etc) the fit out will pay for itself in around 6 months!


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## johna.clements (30 Sep 2022)

The DPM will stop water coming up but will also stop it going down. With you uneven cobble floor some of you legs will be in low points.


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## Fitzroy (30 Sep 2022)

johna.clements said:


> The DPM will stop water coming up but will also stop it going down. With you uneven cobble floor some of you legs will be in low points.


I'd have only put pieces of dpm under each leg then lifted them and stapled to the leg. Additional to avoiding low points it would also let the floor breath from drafts under your floor.


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## Jonm (30 Sep 2022)

Fitzroy said:


> I'd have only put pieces of dpm under each leg then lifted them and stapled to the leg. Additional to avoiding low points it would also let the floor breath from drafts under your floor.


I would be concerned about what mould/fungus will form between the floor and dpm, best if floor can breath, as you say. Personally I would have set small blocks of concrete/tile/brick on mortar to level it and a piece of dpm on top to sit the wood on.


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## Jonm (30 Sep 2022)

David66 said:


> Update - we've moved into our new home and the shed build has begun. Couple of photos below (sorry, last two use portrait orientation, but have uploaded as landscape!).


you are making great progress, thanks for letting us know.


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