Shed insulation advice please!

[scitmon]

Hello, im looking for advice on insulating my shed.

I have ordered some foil backed PIR boards and plywood sheets for the job.

I already have a breathable membrane on the inside face of the cladding. The thickness of my framing is 65mm and the thickness of my PIR boards is 40mm. Do I need to leave an air gap? And if so will a 25mm airgap between the cladding and insulation be sufficient and does this air gap need ventilating?

 

[^woody^]

You don't need an air gap, but as you will have one by default it should be on the outward side of the insulation.

In principle, it's always better to have continuous insulation across the inner face and not just to insulate between the timbers - which leaves cold spots where the timbers are.

 

[catlad]

To which insulated plasterboard would work.

 

[scitmon]

You don't need an air gap, but as you will have one by default it should be on the outward side of the insulation.

In principle, it's always better to have continuous insulation across the inner face and not just to insulate between the timbers - which leaves cold spots where the timbers are.

Thank you for the response, so to clarify it is outside->cladding-> breathable membrane-> 25mm air gap-> 40mm insulation->plywood->inside

is what I should be doing? I don’t see anyway of ventilating the airgap so im hoping it will be ok...

 

[^woody^]

On the inner face after the plyboard, tape the insulation and timber with foil tape to for a vapour barrier.

Was 60/70mm insulation much more than the 400mm sheets? It may be worth it in the long run if you plan on spending any amount of time in there.

 

[scitmon]

Yes I was planning to use foil tape over the cracks between frame and insulation.

I chose 40mm because my frame is 65mm deep and I wanted to leave an air gap as has been advised from other guides and forums that I found in my research.

I don’t plan to spend significant amounts of time, it’s largely just for storage.

 

[catlad]

Well then don't worry about it! If you where using it as an office ect. and pumping heat all day then it could be a different matter.