Building a workshop in an old stone built barn

[Fitzroy]

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.

 

[Ttrees]

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?

 

[johna.clements]

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.

 

[johna.clements]

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.
View attachment 141871
I don't know anything whatsoever about building, but seems to me the shed in a 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?

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.

 

[Ttrees]

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?

 

[johna.clements]

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?

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.

 

[Jonm]

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.

 

[David66]

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?

 

[rogxwhit]

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.

 

[johna.clements]

Many chemicals dissolve polystyrene.

Polystyrene is not good in a fire.

 

[David66]

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?

 

[Jonm]

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?

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”.

 

[rogxwhit]

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.

 

[David66]

"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.

 

[Jameshow]

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

 

[johna.clements]

"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.

 

[Jonm]

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.

 

[David66]

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?

 

[rogxwhit]

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.

 

[David66]

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!!