Retrospective shed insulation

[jcassidy]

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]

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.

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.

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]

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]

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]

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]

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]

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

 

[TheUnicorn]

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]

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.