# Retrospective shed insulation



## Carlos0371 (3 Jan 2021)

Good afternoon all, firstly thank you for allowing me to join, been looking for a group with people who actually know what they're talking about after so much conflicting advice and opinions on Facebook groups.

Secondly, apologies for the rambling post, but I wanted to avoid as many additional questions regarding the construction etc.

Ok, so I have searched, and I have read Mike's way to build a shed, but I still have questions regarding my build. Alas it's not a workshop, but a pub shed (don't judge me, I am adding a pent roof shed to the side of it once I've completed the pub part lol), but hoping to get some proper advice here.

So, it's a pre built 14' x 8' shed (originally from Timberlux buildings) that I've purchased second hand, dismantled, moved, and reassembled. The walls are 3x2 framework with 22mm barrel board cladding, which is ALREADY fixed to the frame, thus making 4 x wall panels and 2 x roof panels which slot/screw together. It has 4 fixed and 1 opening single glazed windows on each side, which I'm hoping to upgrade later.

The roof is 13mm T&G, covered with roof felt, which I'll be replacing with a suitable alternative.

As it's already constructed, I am unable to wrap it in breathable membrane, despite hundreds of posts in other places of people telling me I need to do this.

I need to insulate, and the framework gives me a 70mm (yes I know, just under 3") gap.

Celotex/ Kingspan etc is out of my budget, so looking at a way to insulate as it will be used hopefully all year round, and will have heating (hopefully wood burner).

After trawling the web for days and days I've come to the conclusion I'm overthinking it, and need a simple option, so I'm looking at mineral felt / rockwool in the framework directly against the exterior cladding (external is being treated with Cuprinol 5 year ducks back paint), then OSB internal cladding, which I've read elsewhere on this forum acts as a vapour barrier due to the glue.

I think I also need to install 2 vents in the eaves, one at each end, to allow air circulation from inside to outside.

I'm hoping this will be sufficient to prevent condensation inside, but cannot get a definitive answer from anyone who actually knows what they're talking about.

Obviously if the OSB alone isn't sufficient for the vapour barrier, then I would use plastic sheeting as well, so:
Barrel board external, mineral felt/rockwool, plastic sheeting vapour barrier fixed to the framework internally, with OSB fixed directly over that.

Next up is if I use loft insulation as intended, I'm looking at 100mm knauf stuff on special offer in B&Q at the moment, but this will need to be compressed to fit the 70mm gaps, so is this better than 50mm which would have better airflow?

I'd appreciate any help or advice that any of you can offer, and once again, yes I've read Mike's post, but reiterate I cannot follow all the advice there due to the shed already being built.

Thank you all in advance, and thanks for bearing with my ramblings lol.


----------



## NickVanBeest (3 Jan 2021)

I used "Xtratherm PIR Rigid Insulation Board" followed by 18mm OSB, and it works really well


----------



## Carlos0371 (3 Jan 2021)

NickVanBeest said:


> I used "Xtratherm PIR Rigid Insulation Board" followed by 18mm OSB, and it works really well
> View attachment 100175


As mentioned, PIR beyond my budget


----------



## artie (3 Jan 2021)

Given where you're starting from, I'd seal the cladding as well as possible inside and out, then fill with 50mm polystyrene. It cost just under a tenner per 8 by 4 sheet, last time I bought it. Then line with osb.
I'd put a small vent outside at the top of each partition and a small one at the bottom on the inside.
If you are using a log burner in a 14 by 8 you can afford to lose a bit of air.


----------



## Carlos0371 (3 Jan 2021)

artie said:


> Given where you're starting from, I'd seal the cladding as well as possible inside and out, then fill with 50mm polystyrene. It cost just under a tenner per 8 by 4 sheet, last time I bought it. Then line with osb.
> I'd put a small vent outside at the top of each partition and a small one at the bottom on the inside.
> If you are using a log burner in a 14 by 8 you can afford to lose a bit of air.


Thanks for the reply Artie.

The shed is already treated by the manufacturer, the external paint is just belt and braces. Per square metre the poly works out considerably more expensive (currently over £16 per sheet in B & Q), and I've heard it's not great for fire resistance, although I do have the Jablite stuff in the floor.

With my budget constraints, I'm just looking for someone to advise whether my plan is OK, or a no-no. I've read elsewhere that loft insulation compression has a 95% thermal reduction when compressed, but as it's only going to be 25-30mm compression, I was hoping this would be negligible?


----------



## RobinBHM (3 Jan 2021)

Maybe look at 75mm cavity insulation

Or 100mm loft insulation, but add on 2 x 1 battens to get the cavity to 100mm - that would give you better insulation. Squashing it isn't a great idea.

The disadvantage you have is no cavity behind the external cladding for airflow.


----------



## Carlos0371 (3 Jan 2021)

RobinBHM said:


> Maybe look at 75mm cavity insulation
> 
> Or 100mm loft insulation, but add on 2 x 1 battens to get the cavity to 100mm - that would give you better insulation. Squashing it isn't a great idea.
> 
> The disadvantage you have is no cavity behind the external cladding for airflow.


Thanks Robin,

So if I used 75mm, would I need a vapour barrier on the inside, or could I just go with the insulation then OSB on top?


----------



## RobinBHM (3 Jan 2021)

Carlos0371 said:


> Thanks Robin,
> 
> So if I used 75mm, would I need a vapour barrier on the inside, or could I just go with the insulation then OSB on top?



OSB is quite a good vapour barrier.

In any case I think a plastic vapour barrier in a shed is asking for trouble....it risks condensation and damp.

The methodology of vapour barriers to prevent interstitial condensation is based on the house always being the warm side....not so true in a shed. It's not uncommon for a shed to be unheated, get very cold during the night, then the sun comes out....bingo we have outside warm, inside cold.


----------



## Carlos0371 (3 Jan 2021)

RobinBHM said:


> OSB is quite a good vapour barrier.
> 
> In any case I think a plastic vapour barrier in a shed is asking for trouble....it risks condensation and damp.
> 
> The methodology of vapour barriers to prevent interstitial condensation is based on the house always being the warm side....not so true in a shed. It's not uncommon for a shed to be unheated, get very cold during the night, then the sun comes out....bingo we have outside warm, inside cold.


Hmmmmm I see your point about warm outside.

OK, so how could I combat the risk of condensation effectively with my scenario?

As mentioned, it will be heated during the colder weather, but I need protection in the summer too.


----------



## TheUnicorn (3 Jan 2021)

just a thought, and not from first hand experience, but have you considered sheeps wool / fleece. I gather that they are virtually worthless to the farmers and so are often given away for little or nothing (at the right time of year of course), breathe well and offer very good insulation. It might be worth looking into, maybe some eco build forums etc?


----------



## Carlos0371 (3 Jan 2021)

A lovely thought, and eco friendly, but timing is kind of out here, need to crack on and get this shed done now as it's been dragging on for longer than I had hoped.


----------



## Jameshow (3 Jan 2021)

Second sheeps wool.... 

Being a wood shed and doing woodworking I don't think you will have a moisture issue. 

The shed walls and timber from your wood working in will absorb any moisture and release it slowly. 

Cheers James


----------



## RobinBHM (3 Jan 2021)

Carlos0371 said:


> Hmmmmm I see your point about warm outside.
> 
> OK, so how could I combat the risk of condensation effectively with my scenario?
> 
> As mentioned, it will be heated during the colder weather, but I need protection in the summer too.



I think your biggest risk is rain water getting behind the cladding. In an ideal world you would have a small cavity then breathable membrane. Without that, I would go for fibreglass or Rockwell insulation which can't rot or harbour damp much and don't compress it.

OSB will limit vapour movement but isn't a cold surface so it wont encourage condensation.


----------



## TheUnicorn (3 Jan 2021)

have just been reading around a bit about using unprocessed fleeces for insulation (it was my idea, but it was just something I'd come across in passing, no experience of it). it seems that there are quite a few issues with smell and moths, but a manuafactured sheeps wool product might still be an option, though I'm not sure how it compares cost wise


----------



## Carlos0371 (3 Jan 2021)

RobinBHM said:


> I think your biggest risk is rain water getting behind the cladding. In an ideal world you would have a small cavity then breathable membrane. Without that, I would go for fibreglass or Rockwell insulation which can't rot or harbour damp much and don't compress it.
> 
> OSB will limit vapour movement but isn't a cold surface so it wont encourage condensation.


Ok so I'm looking at 75mm rockwool/fibreglass, and OSB internally, no chapter barrier needed?


----------



## Fitzroy (3 Jan 2021)

I think you know your idea has compromises vs the ideal, the trouble is no-one can quantify them. Each compromise on the ideal increases the likelihood of condensation or penetrating moisture (wind blown rain, melting ice) remaining for long periods and allowing rot to set in, or getting to the internal finished surface and causing unsightly damp patches in your work environment. 

Proceeding with your plan as stated will likely be fine for multiple years, even untreated wood sitting wet will give you five. However as the years push on 7, 10, 15 you’ll start to see the issues with your compromises. 

There is also an active post on here about a condensation issue that has made a space unusable after only weeks. However the factors effecting that build are quite specific. 

No one can assure you your idea is problem free as else all buildings would be built as simply as your proposing. Folks will likely give you some suggestions to minimise the compromises you have to make. After that you make a decision and history will be the judge. My workshop build was not precisely ‘Mikes Way’ but for each compromise I made the decision based on what I could achieve and the advice given. 

Personally for your situation I’d be trying to get a ventilated gap between the insulation and outside boards. This will give the best chance of stuff drying out. 

The main problem with loft insulation in walls is it slumps, getting a gap behind something that slumps is difficult. 

My 2p worth. Add a 50mm batten internally to each stud increasing the depth to 125mm. Staple in a breathable membrane from the inside into each wall section with a 25mm gap to the boards. Use 75 or 100mm rockwool rwa45 between studs, it will self support. OSB on the inside. 

Same on the roof, venting at the eves. EPDM on the roof to replace felt. 

Fitz.


----------



## johnnyb (3 Jan 2021)

I reckon your method is really poor tbh. what will happen is moisture will pass through the rock wool and condense on the cladding causing mould.


----------



## Carlos0371 (3 Jan 2021)

johnnyb said:


> I reckon your method is really poor tbh. what will happen is moisture will pass through the rock wool and condense on the cladding causing mould.


Not sure that's the case to be honest, how will moisture pass from the warmth inside to the colder outside if the OSB is acting as a barrier?


----------



## Carlos0371 (3 Jan 2021)

Fitzroy said:


> I think you know your idea has compromises vs the ideal, the trouble is no-one can quantify them. Each compromise on the ideal increases the likelihood of condensation or penetrating moisture (wind blown rain, melting ice) remaining for long periods and allowing rot to set in, or getting to the internal finished surface and causing unsightly damp patches in your work environment.
> 
> Proceeding with your plan as stated will likely be fine for multiple years, even untreated wood sitting wet will give you five. However as the years push on 7, 10, 15 you’ll start to see the issues with your compromises.
> 
> ...


Sound reasoning there Fitz, just really not keen on extending all the framework by another 2 inches either side all around, due to the additional work / cost involved. RWA45 is also prohibitively expensive to my budget. Trust me I've looked at all the options on this, and because of my gaps being various sizes (465, 550, 620, 700mm are just some of the random spacings) I'm really trying to negate waste as much as possible, which I imagine is going to mount up considerably with the batt stuff.

I'm just trying to clarify your details, do you mean install breathable membrane in the gaps between the frame leaving a 25mm gap between that and the OUTSIDE boards? This would be quite fiddly to make sure the membrane stays taut between the frame wouldn't it?

How about using polystyrene insulation as someone has mentioned to me instead?

Also, venting each partition could prove awkward as well, as to vent every partition would require 7 vents each side, and 4 on each of the end panels.


----------



## Jameshow (3 Jan 2021)

Another thought. 

How about no insulation. 

When you put the OSB board on your creating a sealed unit which in and of itself will insulate. Of your working in the shed an oil filled rad and your body heat will warm it. 

Or what about foil bubble wrap it's what the camper van community use. 

Cheers James


----------



## Woody2Shoes (3 Jan 2021)

Hi Carlos,
what will be the actual use of the shed? You say it's attached to a pub, but....For example, you plan to heat it - with what type of appliance? Will there be any other sources of heat/moisture e.g. washing facilities?
A lot of condensation probs are actually caused by the occupants and their actions.

Your barrel boards are in effect a 'rain screen' and you can expect them to get wet through in an exposed situation or if water from the roof/eaves is not fully dealt with. Therefore these cladding boards will need to be able to dry out (from both inside side and outside side) so their inside will need to be ventilated.
Don't forget that OSB usually needs to be installed with a 3mm gap all round. I do not 100% buy the argument that OSB is vapour impermeable - it certainly has a lowish vapour permeability, but is not impermeable. Any insulation will cease to function as such if it gets saturated with moisture - rockwool has an advantage in that it can dry out quite quickly because it is (if uncompressed) very vapour permeable.
There is no ideal solution given your constraints.


----------



## Carlos0371 (3 Jan 2021)

Jameshow said:


> Another thought.
> 
> How about no insulation.
> 
> ...


Foil bubble wrap was another consideration, but opinions again are very divided on how insulating it really is, as opposed to just reflecting the heat back in and the cold back out.

Regarding no insulation, I'd hate to do that then it be effing freezing and need to pull the OSB off and sort it later.


----------



## Carlos0371 (3 Jan 2021)

Woody2Shoes said:


> Hi Carlos,
> what will be the actual use of the shed? You say it's attached to a pub, but....For example, you plan to heat it - with what type of appliance? Will there be any other sources of heat/moisture e.g. washing facilities?
> A lot of condensation probs are actually caused by the occupants and their actions.
> 
> ...


Hi Woody, sorry my initial post wasn't clear; the 14 x 8 main structure is going to be a pub / TV room / summer room if you like, used for entertaining, watching footy, kids to chill out etc. The shed is a separate part that I'm going to build onto the outside of the main structure, but at a later date.

I'm hoping to put in a small wood burner, which eats into my budget considerably. The whole reason for having a tight(ish) budget rather than being a bit more extravagant is that we are only renting, and obviously run the risk of having to move at any time, although the landlords have made it clear they want us here long term.

No other heat sources, but people will obviously create their own problems moisture wise.


----------



## Woody2Shoes (3 Jan 2021)

I think that you'd be best with just 11mm OSB3 on the inside and no insulation. Just about any log burner once fired up will make it too hot even on a cold night!


----------



## NickVanBeest (3 Jan 2021)

Renting as well, hence my shed is modular panels, 90cm wide, bolted together, each panel insulated as a whole... not ideal, but it works, and will be easy to break down and take with me


----------



## Woody2Shoes (3 Jan 2021)

Woody2Shoes said:


> I think that you'd be best with just 11mm OSB3 on the inside and no insulation. Just about any log burner once fired up will make it too hot even on a cold night!


Don't forget that (dryish) air is a pretty good insulator...


----------



## Carlos0371 (3 Jan 2021)

NickVanBeest said:


> Renting as well, hence my shed is modular panels, 90cm wide, bolted together, each panel insulated as a whole... not ideal, but it works, and will be easy to break down and take with me


Absolutely no chance this will be coming with us if we do have to move lol.


----------



## Carlos0371 (3 Jan 2021)

Woody2Shoes said:


> Don't forget that (dryish) air is a pretty good insulator...


Yes, was just trying to maximise the insulation and thought loft insulation would be a good value solution.


----------



## Woody2Shoes (3 Jan 2021)

I think it would be a waste of money - I'd put the effort into detailing the ventilation. As I say, this shed is not large and will be easy to keep cosy with the woodburner, cheers, W2S


----------



## Carlos0371 (3 Jan 2021)

Woody2Shoes said:


> I think it would be a waste of money - I'd put the effort into detailing the ventilation. As I say, this shed is not large and will be easy to keep cosy with the woodburner, cheers, W2S


OK Woody thanks. Would appreciate the views of anyone else who concurs with this opinion?


----------



## mikej460 (3 Jan 2021)

Given you are going to install a wood burner I would focus on keeping damp, cold air out so a relatively cheap roll of foil insulation which if overlapped by 100mm and taped with aluminium foil would be your vapour barrier. You can then line with whatever you can afford. If your budget allows you could get slabs of much cheaper polystyrene insulation to fit between the struts. If you search this website there are some useful videos Timber Frame & Foil Insulation | YBS Insulation 

I've used YBS Superquilt extensively when drylining our old cottage but this is over the top for what you need so take a look at their other products.

Don't forget ventilation and a carbon monoxide alarm for the burner.


----------



## Fitzroy (3 Jan 2021)

Carlos0371 said:


> Sound reasoning there Fitz, just really not keen on extending all the framework by another 2 inches either side all around, due to the additional work / cost involved. RWA45 is also prohibitively expensive to my budget. Trust me I've looked at all the options on this, and because of my gaps being various sizes (465, 550, 620, 700mm are just some of the random spacings) I'm really trying to negate waste as much as possible, which I imagine is going to mount up considerably with the batt stuff.
> 
> I'm just trying to clarify your details, do you mean install breathable membrane in the gaps between the frame leaving a 25mm gap between that and the OUTSIDE boards? This would be quite fiddly to make sure the membrane stays taut between the frame wouldn't it?
> 
> ...



Yes a gap to the outside boards. It would be fiddly but a lower cost compromise. RWA45 varies lots in cost I’m looking at about £4.5/m2, rough calcs you have 45m2 of wall and roof area, so £200 on insulation, 100mm loft insulation is about £125. I think the loft insulation would be a false economy as it’ll slump over time and I’d be doubtful on its performance. I’d likely choose no insulation as a preference. 

Regard vents, if you did insulate with a gap. Only in the roof. The outer boards will have gaps that will offer sufficient ventilation to the wall cavities. The roof layer will be impermeable, so will only dry through ventilation. 

Regards experience heating an unisulated shed. My shed/workshop has yet to be insulated, walls are stud work, 18mm osb, breather membrane, battens, 15mm larch cladding (said it wasn’t mikes way) roof is 18mm osb and EPDM. It has soffit vents fir a cold roof design, eventually, so is well ventilated. A 1.5kw fan heater gets it up to 15degC after a couple of hours. A 5kw wood burner it would be toasty, oh it’s 20’x10’. 

Fitz.


----------



## Carlos0371 (3 Jan 2021)

mikej460 said:


> Given you are going to install a wood burner I would focus on keeping damp, cold air out so a relatively cheap roll of foil insulation which if overlapped by 100mm and taped with aluminium foil would be your vapour barrier. You can then line with whatever you can afford. If your budget allows you could get slabs of much cheaper polystyrene insulation to fit between the struts. If you search this website there are some useful videos Timber Frame & Foil Insulation | YBS Insulation
> 
> I've used YBS Superquilt extensively when drylining our old cottage but this is over the top for what you need so take a look at their other products.
> 
> Don't forget ventilation and a carbon monoxide alarm for the burner.


Thank you, I'll take a look.


----------



## Carlos0371 (3 Jan 2021)

Fitzroy said:


> Yes a gap to the outside boards. It would be fiddly but a lower cost compromise. RWA45 varies lots in cost I’m looking at about £4.5/m2, rough calcs you have 45m2 of wall and roof area, so £200 on insulation, 100mm loft insulation is about £125. I think the loft insulation would be a false economy as it’ll slump over time and I’d be doubtful on its performance. I’d likely choose no insulation as a preference.
> 
> Regard vents, if you did insulate with a gap. Only in the roof. The outer boards will have gaps that will offer sufficient ventilation to the wall cavities. The roof layer will be impermeable, so will only dry through ventilation.
> 
> ...


Thanks Fitz for the clarification. More things to consider, so thanks again for taking the time.


----------



## Inspector (3 Jan 2021)

It's kind of in the landlords best interest that you do a proper job on the shed and to that end credit some of what you spend off the rent. Now if this is being done without permits, inspections or planning approval, whatever you call non conforming, and be subject to removal if found out then he/she is under no obligation and might be liable for removal costs down the road. If the structure had been built like we do here, not MikeG approved,  OSB outside on the 2 x framing, breathable membrane and then sided, you could have insulated, put up plastic vapour barrier and then drywalled the inside. If mine now I would put vents at the top and bottom of the stud cavities, put styrofoam sheets right across the inside of the walls, caulking, taping, or foaming the edges and then drywall (maybe the waterproof kind for bathrooms) the inside. As a renter I would have just parked a trailer / caravan and played in it. You can take it with you or sell when you move. Good luck whatever route you take.

Pete


----------



## Carlos0371 (3 Jan 2021)

Inspector said:


> It's kind of in the landlords best interest that you do a proper job on the shed and to that end credit some of what you spend off the rent. Now if this is being done without permits, inspections or planning approval, whatever you call non conforming, and be subject to removal if found out then he/she is under no obligation and might be liable for removal costs down the road. If the structure had been built like we do here, not MikeG approved,  OSB outside on the 2 x framing, breathable membrane and then sided, you could have insulated, put up plastic vapour barrier and then drywalled the inside. If mine now I would put vents at the top and bottom of the stud cavities, put styrofoam sheets right across the inside of the walls, caulking, taping, or foaming the edges and then drywall (maybe the waterproof kind for bathrooms) the inside. As a renter I would have just parked a trailer / caravan and played in it. You can take it with you or sell when you move. Good luck whatever route you take.
> 
> Pete


OK, here goes:

Our choice to build so no obligation from the landlord to reduce rent,
Permission obtained so won't be any need to remove it IF we leave,
Regulations - none required for this size,
Could've, should've, would've........
Trailer / caravan, no chance as it's an enclosed rear garden with no access. It was hard enough getting the shed panels round the back through the public park, through the overgrowth and over the fence.

Thanks for your input though.


----------



## Jameshow (3 Jan 2021)

Another thought

Look at insulation seconds on eBay there maybe some near you. Also building sites esp big housing jobs often throw out stuff they don't need. 

Just a thought....

Cheers James


----------



## mikej460 (3 Jan 2021)

Carlos0371 said:


> Thank you, I'll take a look.


No problem and there are more ideas here
insulating a shed uk - YouTube


----------



## Carlos0371 (3 Jan 2021)

Jameshow said:


> Another thought
> 
> Look at insulation seconds on eBay there maybe some near you. Also building sites esp big housing jobs often throw out stuff they don't need.
> 
> ...


Have tried this, just my luck though, nothing anywhere near me


----------



## mg123 (4 Jan 2021)

I'd be inclined to not add insulation between the walls due to the damp risk, especially not loft type as it would slump. The foil/bubble wrap insulation added over the wall battens would help speed up the heating and also provides the vapour barrier if you follow the guidelines. You could add roof battens over that and then add the osb over the top and you've got a more cost effective option. 
Another thought on heating, have you considered going down the diesel burner type? They appear to be very cost efficient and offer upto 8kw output so would get the temperature up very quickly. You'd obviously need an electrician if you're not confident in doing that work as they're intended for motor homes so use a 12 vault supply. That's the route I'm going down, i looked at getting a log burner but the diesel heaters seem to be a much better option.


----------



## jcassidy (4 Jan 2021)

Given your limitations, which are entirely reasonable, I'd be inclined to go with either no insulation at all, or bubble-wrap/cladding, which is minimal but should help get the temp up quicker and keep cold draughts out. The key will be ventilation.


----------



## Wayside2020 (4 Jan 2021)

Carlos0371 said:


> Good afternoon all, firstly thank you for allowing me to join, been looking for a group with people who actually know what they're talking about after so much conflicting advice and opinions on Facebook groups.
> 
> Secondly, apologies for the rambling post, but I wanted to avoid as many additional questions regarding the construction etc.
> 
> ...


It sounds like you have worked it out yourself. If you want the building to last you need to try and install a vapour barrier. If you don’t fancy pulling the boards off and doing it that way. I would wrap it internally horizontally and staple it on. 
Good luck.


----------



## Carlos0371 (4 Jan 2021)

Wayside2020 said:


> It sounds like you have worked it out yourself. If you want the building to last you need to try and install a vapour barrier. If you don’t fancy pulling the boards off and doing it that way. I would wrap it internally horizontally and staple it on.
> Good luck.


You mean against the external boards on the inside?

Removing the boards isn't an option, as they are nailed on, with a nail gun so the heads are completely recessed.


----------



## Wayside2020 (4 Jan 2021)

Carlos0371 said:


> You mean against the external boards on the inside?
> 
> Removing the boards isn't an option, as they are nailed on, with a nail gun so the heads are completely recessed.


Yes against the boards. It means you will have to follow the shape of the frame. I should of said membrane not VB. 
I built my own home and it is timber construction. The frame manufacturer stressed the importance of the membrane and gave me a history lesson on its development to insure robust building regs compliance. 
I have scratch built several large sheds and a workshop this way and still going strong 20 years on.


----------



## Carlos0371 (4 Jan 2021)

Wayside2020 said:


> Yes against the boards. It means you will have to follow the shape of the frame. I should of said membrane not VB.
> I built my own home and it is timber construction. The frame manufacturer stressed the importance of the membrane and gave me a history lesson on its development to insure robust building regs compliance.
> I have scratch built several large sheds and a workshop this way and still going strong 20 years on.


Thank you. My guess is that something is better than nothing, right? I'm probably going to go polystyrene sheets for the insulation now as they're more robust and less likely to flop down. Would I still need a vapour barrier on the inside, i.e. fixed to the frame? I'm now using t&g cladding internally as well (cost), so the VB properties of the OSB are negated.


----------



## Woody2Shoes (4 Jan 2021)

Carlos, I'm posting again somewhat against my better judgement. Forgive me, but you seem to be fixed in your plan and simply casting around for support for it!
This shed is considerably smaller than a single garage!
My neighbour has an uninsulated concrete sectional (much much worse insulation than a timber shed like yours) single garage with a fibre sheet roof. He uses it as a workshop, and goes from cold to shirt-sleeves in about 15 mins - in January - with a small 3kW woodburner. Of course for half the year he needs no heating at all and on sunny days works with the door open!
Your, money, your choice...


----------



## Rorschach (4 Jan 2021)

If you are planning to heat with a woodburner don't waste your money on insulation, you will be working with the door open soon after firing it up.


----------



## brittonc (4 Jan 2021)

Some interesting reading. I'm in a similar position. I have a shed being delivered next week and have been looking at using rockwool, not only for insulation but also sound proofing. Don't want to be annoying the neighbours too much! It's 18' x 8' so will only be using an oil filled rad for heating so would like to retain as much heat as possible. Not 100% sure what depth the framework is but was planning on just putting rockwool between the outside wall and using ply or OSB to board it up. Now I'm not sure with comments about vapour barriers, foils etc!


----------



## Wayside2020 (4 Jan 2021)

Carlos0371 said:


> Than you. My guess is that something is better than nothing, right? I'm probably going to go polystyrene sheets for the insulation now as they're more robust and he's likely to flop down. Would I still need a vapour barrier on the inside, i.e. fixed to the frame? I'm now using t&g cladding internally as well (cost), so the VB properties of the OSB are negated.


Yes. And any insulation is better than none. Despite what some are saying. The UK is very cold and damp in the winter and any cold metal work will quickly rust.


----------



## Woody2Shoes (4 Jan 2021)

This guy talks a lot of sense. If you study some of the other vids on his channel you may improve your understanding of the issues involved:

Obviously roofs (you haven't mentioned floor and roof?) and walls operate similarly...


----------



## Carlos0371 (4 Jan 2021)

Woody2Shoes said:


> Carlos, I'm posting again somewhat against my better judgement. Forgive me, but you seem to be fixed in your plan and simply casting around for support for it!
> This shed is considerably smaller than a single garage!
> My neighbour has an uninsulated concrete sectional (much much worse insulation than a timber shed like yours) single garage with a fibre sheet roof. He uses it as a workshop, and goes from cold to shirt-sleeves in about 15 mins - in January - with a small 3kW woodburner. Of course for half the year he needs no heating at all and on sunny days works with the door open!
> Your, money, your choice...


Ok thank you again Woody, and I guess you're right, I kind of had it in my head that the shed really does NEED to be insulated, if only to stop condensation/damp/mildew.

What I've finally settled on, and please please advise me again if you think this is wrong, is breathable membrane stapled to the external cladding in each of the sections, plastic vapour barrier detailed to the frame internally, with tongue and groove cladding over the top of that. No insulation in the cavities. 

It's my understanding that this will at least hellp the moisture in/out from the outside, and prevent the warm air escaping from inside.

Roof:
Ventilation in the roof with vents at each end in the eaves, no moisture barrier, tongue and groove cladding internally, but again no insulation. Roof to be replaced with (probably) EDPM or similar waterproofing.

Let me know your thoughts on this. Cheers.


----------



## Woody2Shoes (4 Jan 2021)

Wayside2020 said:


> Yes. And any insulation is better than none. Despite what some are saying. The UK is very cold and damp in the winter and any cold metal work will quickly rust.


I think that rust prevention is a very different topic - a low wattage electric heater in a tool cupboard may well be a much better solution. This is a summer-house/'pub' not a workshop we understand.


----------



## Woody2Shoes (4 Jan 2021)

Carlos0371 said:


> Ok thank you again Woody, and I guess you're right, I kind of had it in my head that the shed really does NEED to be insulated, if only to stop condensation/damp/mildew.
> 
> What I've finally settled on, and please please advise me again if you think this is wrong, is breathable membrane stapled to the external cladding in each of the sections, plastic vapour barrier detailed to the frame internally, with tongue and groove cladding over the top of that. No insulation in the cavities.
> 
> ...


I don't think the breathable membrane does anything for you in this situation, I'd leave it out. You ideally need to find a way for air to circulate from floor to ceiling in each 'bay' to allow your 'cavity' to dry out.


----------



## Carlos0371 (4 Jan 2021)

Also should mention with the roof that there is excellent ventilation along the sides, as there is a gap between the overhang of the roof and the shed wall, i.e. The roof does not sit snugly on the wall (if that makes sense?).


----------



## Carlos0371 (4 Jan 2021)

Woody2Shoes said:


> I don't think the breathable membrane does anything for you in this situation, I'd leave it out. You ideally need to find a way for air to circulate from floor to ceiling in each 'bay' to allow your 'cavity' to dry out.


Again sorry to sound like a stuck record, but floor to ceiling ventilation is very difficult due to the construction.

Should probably have included some more photos originally, but here they are now. Also included where the roof sits on the walls, showing there is airflow direct to outside, as well as showing the gap in the overhang outside.


----------



## Woody2Shoes (4 Jan 2021)

Carlos0371 said:


> Again sorry to sound like a stuck record, but floor to ceiling ventilation is very difficult due to the construction.
> 
> Should probably have included some more photos originally, but here they are now. Also included where the roof sits on the walls, showing there is airflow direct to outside, as well as showing the gap in the overhang outside.


Sorry to sound like a stuck record but:
a) It really isn't difficult - it looks like you've got your eaves-level ventilation sorted already (although you'll be wanting some kind of mesh to stop insects/birds/mice getting in)! And,
b) It is important.


----------



## Carlos0371 (4 Jan 2021)

Woody2Shoes said:


> Sorry to sound like a stuck record but:
> a) It really isn't difficult - it looks like you've got your eaves-level ventilation sorted already (although you'll be wanting some kind of mesh to stop insects/birds/mice getting in)! And,
> b) It is important.


Aha, so mesh along the outside edge of the overhang, roof ventilation sorted, but what about the walls, as there are horizontals running below the windows which basically stop any airflow from the floor up to the eaves. How about cross venting through the verticals and vents at the top in each of the end panels?


----------



## cowie122 (4 Jan 2021)

I would use Rockwool for the insulation as it is water repellant Batts rather than the roll would be best


----------



## TheUnicorn (4 Jan 2021)

re. floor to ceiling ventilation, I've no experience of shed building, so take this with a pinch of salt, but if you mount a board on the walls, leaving an inch at the top (or in some cases just below the window sill) and an inch at the bottom, have you not achieved airflow fairly quickly and easily?


----------



## jcassidy (4 Jan 2021)

I think you're overthinking it. We're already past the winter solstice. Install that woodburner you mentioned and see how you get on uninsulated. If it's intolerable, start by sealing gaps that the wind is getting through. It might all be on one side if you have a strong prevailing wind. 

For the longest time, my shed was windproofed by bits of cardboard stuffed into the gaps at the eaves, and strips of cardboard jammed into the floorboards with PVA glue, acting as caulking.

By next autumn, you'll have a better idea of your long-term plans and can invest accordingly.


----------



## Fergie 307 (5 Jan 2021)

mg123 said:


> I'd be inclined to not add insulation between the walls due to the damp risk, especially not loft type as it would slump. The foil/bubble wrap insulation added over the wall battens would help speed up the heating and also provides the vapour barrier if you follow the guidelines. You could add roof battens over that and then add the osb over the top and you've got a more cost effective option.
> Another thought on heating, have you considered going down the diesel burner type? They appear to be very cost efficient and offer upto 8kw output so would get the temperature up very quickly. You'd obviously need an electrician if you're not confident in doing that work as they're intended for motor homes so use a 12 vault supply. That's the route I'm going down, i looked at getting a log burner but the diesel heaters seem to be a much better option.


You really do need a breathable membrane between the outside wall and any insulation. Unless you do this your insulation will get wet over time and cause damp or worse still rot to start in the outside panelling and structure. Your best bet would be to cover the inside with breathable membrane, stapled to the inside of the frame, so you have the thickness of the frame as an air gap. Then you will need to put new battens inside at a suitable spacing for you chosen insulation. Personally I would use Rockwood batts. These will not slump and are easy to cut to shape. Then put your inside covering over the top. I have used chipboard flooring sheets, strong water resistant and cheap. I know you don't want to go to the expense and trouble, but at the end of the day this method is the only proper way to do it and avoid long term problems. Also if you intend to use a wood burner you MUST provide suitable vents to enable it to draw air in, otherwise it will suck all the oxygen out in no time. Someone mentioned diesel burners. These are excellent. I have two 8kw units in my workshop, which is 10 x 8m and 3m high. As an aside you could save yourself a lot of expense by just not insulating the walls at all. My shed has a 25mm gap between featherboards and a breathable membrane. The frame is 4x2 with chipboard flooring panels as the internal cladding. I have no insulation in the walls, but 6 inches in the roof. No issues with damp and it heats up very quickly, and hold the heat well. I have numerous machine tools which feature a lot of bare steel and have never had any issues whatsoever with damp or corrosion.


----------



## ivan (5 Jan 2021)

Please don't use rockwool, or other fibre products, as if you get any penetration of the weatherboarding, the insulation will hold water and not dry out. This is worse than no insulation. We actually have this problem in our house built 1986 - rockwool in the cavity is wet caused by shoddy building; NHIB refused to resolve. At last can afford to get it replaced. Use a waterproof board material, spaced away from the cladding and stuck with gunned adhesive, and make this gap vented to the outside, probably from underneath and under the eaves, would be the easiest solution. Membrane and battens as above better, and fibre batts now OK. Think about a dehumidifier, but not the compressor type which do not work well at low temperatures. Cost you about £200 and will keep all rusting at bay.


----------

