Insulating a Single Skin Brick Shed for part time office

[futureechos]

Hi,

I want to insulate an 8x3m shed for part time office use, possibly partition off half so there is a smaller area to heat.

I was thinking insulated plaster with foil, dot and dab it in and seal with tape. Walls have damp course and it’s a concrete base.

Don’t want to spend a fortune on this so what’s the simplest approach that won’t cause issues in the future.

Shed is dry inside and has been in place for 15 years roughly.

 

[Notch7]

If the inside is dry, you could stick insulation directly to the walls, tape the joints, then screw on 50 x 25mm battens laid flat and plasterboard to that.

It does mean no cavity so slight risk of damp build up, however on the plus side, the celetex will be total cover with no thermal bridging and the battens create a space for electric cables and they provide fixings for plasterboard. You would of course need to cut out the back of some of the insulation to avoid the roof straps

the electric cables would be less than 50mm from the surface so you would need to follow safe zones rules


the problem with insulated plasterboard is that the insulation and plasterboard joints are all in line with each other -which with dot and dab might make it difficult to line up

 

[23vc]

There have been a few recent posts on this, centred around notch’s PIR trapped to wall by battens plus a dpm lapped to floor and ceiling I think

 

[Ivor Windybottom]

Those pillars are a problem, you have to choose whether to bump out your insulation over them or not, which would create a cold(er) spot... probably OK in reality if building control isn't involved.

You could batten or frame across them, with a frame between them. But you would lose a fair bit of room doing this.

Are the pillars half-brick or full-brick depth? I can't tell from the photo.

If they're half-brick depth I'd fill out alcove between them with PIR insulation, perhaps 75mm, with battens on top of the PIR up to the level of the pillars, then a membrane over the lot with plasterboard over that screwed through. Perhaps glue or spray foam over the pillars where the board spans across them.

If they're full-brick depth (hopefully not) then you'd probably need to make a more complicated inner wall that bumps out over them.

 

[futureechos]

> Are the pillars half-brick or full-brick depth? I can't tell from the photo.

Half Brick.

 

[Ivor Windybottom]

Good. As I say I'd be tempted to put plasterboard directly over them, just with a polythene membrane over as a vapour barrier. Actually foil-backed plasterboard would be a more practical method, then you could bed/glue this directly onto the brick. BUT this isn't the correct thing to do, as they will create a cold spot on the internal walls. In reality this will probably add little or nothing to your heating bills. But if you insulate further then, with or without bumps over them, your room inside is shrinking.

I welcome disagreement from others - I'm merely suggesting what I see is a compromise between doing it properly and maximising the internal space, all assuming building control aren't involved. I fully accept that I'm suggesting a botch!

 

[futureechos]

One follow up question - for the gaps in the roof joists - what is the best approach here?

Batton and Rock Wool style insulation or more foam board insulation?

thanks so much.

 

[futureechos]

Just for my understaning - you mentioned 'Building Control'. At what point should you involve building control - is that required / recommended here?

This is a brick shed at the bottom of the garden - what Building Control or standards do I need to think about other than those mentioned already (safe zones for cabling etc.)

Thanks.

 

[Ivor Windybottom]

If the OSB is the roof surface then you need a 50mm gap under it with free flowing air from both ends of each joist run.

Celotex/PIR board is a much better option. I pinned a bead of the smallest timber from B&Q the height of the PIR boards from the bottom of each joist then banged the PIR into it. Then sealant around the perimeter before boarding over.

 

[Ivor Windybottom]

I wouldn't worry about BC myself, but others may disagree. Potentially if you sell it then a buyer's solicitor might demand a certificate. In which case you tell them there isn't one and the likelihood is that nobody will care.

 

[Notch7]

Those pillars are a problem,

they are a bit of a pain but the celetex just needs to go around them

 

[Ivor Windybottom]

My suggestion is that the plasterboard goes straight over them. Which may be controversial!

 

[Notch7]

At what point should you involve building control - is that required / recommended here?

if its an outbuilding not attached to the house and under 30sq m internally ti doesnt need B/regs



strictly speaking if its closer than 1 metre to the boundary and between 15sq m and 30sq metres it needs B/regs if materials within 1 metre are combustible, or protected by a non combustible material, As its brick outside, that makes it exempt (reason for rules is to ensure there is a 1 metre firebreak to the boundary

 

[Ivor Windybottom]

I did wonder. I know a garage conversion does (officially) require approval. If it's going to be used as living space then it would make sense to at least try and follow the same principles. Garages often have similar pillars, and I'd suggest that you wouldn't be allowed to plasterboard straight over them as I'm suggesting.

It's one of those things where you need to balance rules and theory against practicality. I suspect that bulging the walls into the room to allow some insulation over the pillars probably wouldn't make much difference to its overall insulation level and heating cost. Basically about 5% of the wall would be exactly the same scenario as countless old homes with solid walls and plaster, the other 95% would be far better. It wouldn't comply with modern standards, but it's the real world.