Garden office (read posh shed) insulation help

[feasty33]

Hi all,

Am part way through building a garden office to use as, well, an office.

I've built it from scratch using 2x4 & 2x2 studwork and then clad it in loglap T&G cladding.
The base is made up from a 2x4 frame on short stilts.
This was to get it up off the ground and also to level it out.
The floor is 18mm T&G chipboard with 50mm celotex under it between the joists.
Heating will be by either an oil filled electric radiator or underfloor heating, not decided yet.

That's as far as I've got, and I'm now starting to have doubts about the method of insulation I'm planning on for the walls and ceiling

My original plan was to fit 50mm celotex between the wall studwork and cover it in plasterboard.
The ceiling would be the same, but with 100mm celotex.
There would be no airgap between interior plasterboard and exterior cladding.

I'm now extremely worried that it'll suffer with condensation build up, and I don't know what to do!
I've read about leaving an airgap between exterior cladding and celotex, but then I've also read about leaving the airgap between interior plasterboard and celotex.

Does anyone have the definitive solution??
I'm very scared of getting this bit wrong!

TIA

Dave

 

[fmck]

Hi there. You will need to seal inside with polythene and tape. This is to prevent the warm air inside reaching and condensating on the cold surface in the wall. Goes on inside on top of insulation before plasterboard. Some just tape the joints on the insulation board but a good vapour barrier of polythene is little expense.
The exterior cladding does need to vent or areas will remain damp. Some simple strapping put on with the cladding attached would be suffice. Not sure what you could do if the cladding is already on maybe you will be alright if its 100 percent waterproof.

If your cladding is already on you could keep your insulation thickness so it's less than the thickness of the framework. Holes would need drilled through dwangs etc to ensure there's a passage of air through all voids. External vents top and bottom will allow an air flow. Just a thought.

 

[feasty33]

Hi FMCK,

Thanks for your reply.

The cladding is already mounted to the 2x2 studwork.

So am I right in thinking that my best option would be to add an extra batten to the studs to increase the depth, put 50mm celotex inbetween studs leaving an airgap to the cladding, then polythene and tape over that, then plasterboard tight up to the polythene?

Same with the ceiling, but 100mm celotex?


TIA

Dave

 

[ban-all-sheds]

The cladding is already mounted to the 2x2 studwork.

Remove it and put a breather membrane, e.g. Tyvek, under it?

 

[fmck]

The cladding is already mounted to the 2x2 studwork.

Remove it and put a breather membrane, e.g. Tyvek, under it?

Forgot about that here's what I did with mine before fitting cladding. The straps are vertical to give an air path. The soffits will (still building) have soffit vents to vent out of and vent the roof.

Untitled

• fmck
• 1 Jun 2013
• 2

Making mistakes is all part of the process we don't build garden offices every day so it should be expected.

BTW: "ban -all-sheds" doesn't hate sheds as I first thought he just has a sort of one man crusade against DIY stores

 

[ban-all-sheds]

Forgot about that here's what I did with mine before fitting cladding.

Indeed.

But the OP has already fitted his cladding - I was suggesting he might consider removing it so that he can install a breather membrane.

Making mistakes is all part of the process we don't build garden offices every day so it should be expected.

No, but we could do a bit of research first, asking questions on fora like this, or dedicated shed-building ones, looking at the spec of off-the-shelf garden buildings etc.