Insulating Shed - To Air Gap or not

8 Sep 2020
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United Kingdom
Hi all,

Just in the process of constructing a new pre-fabbed shed. Planning to store some tools and a few other bits in there so want to make sure it's insulated.

At the moment the shed has 40mm studs. I've picked up some Thermal foil insulation (acts as a vapor barrier), and was also planning to get some celotex too.

I'm reading conflicting info though on the best way to go about actually insulating it. Do I need to leave an air gap or not? My main worry is condensation building up in the gap and not escaping.

If I do leave an air gap (say 20mm) what's the best way to layer materials? Should it be:

Foil attached to cladding - air gap - celotex - MDF/OSB


Cladding - air gap - Celotex - Foil - MDF/OSB

OR should I just get 40mm celotex, leave no air gap and pack the gap with foil, then celotex then board?

Or should I not have the vapor barrier at all? Definitely do not want to trap any moisture inside the shed or create damp/mouldy conditions.

Any help greatly appreciated!
Last edited:
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cladding - celotex - foil taped joints- osb

Are you planning to heat the shed? If not, there isn't much point in insulating it.

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