Insulating walls of garden room with insulating foil

Elmroad82

Hi, I have a cabin/ garden room made of 40mm timber. I plan on putting 8mm tongue and groove on the inside to improve the aesthetics.… but thought in the process I could increase its insulation…

If I put thermawrap insulation foil between the timber and tongue and groove (link below), will it provide noticeable insulation? 

Are there better / other alternatives? The room isn’t that big and I don’t have that much free time so I don’t want to pack it out with thick celotex insulation and stud walls..
and finally, is there a downside to using this foil ie damp accumulation on the back / front of the foil? 

Any advice would be appreciated!

https://www.homebase.co.uk/thermawrap-general-purpose-wrap-7.5m/12804774.html

FreeBear

Thermawrap is just metalised foil with a bubblewrap core. It will reflect some heat back, but do little to prevent conductive losses. The best performing insulation for price & thickness is Celotex type rigid boards. Even just 25mm will outperform Thermawrap. 40mm thick boards will fit between your studs and won't eat in to the floor space.

Elmroad82

Hi,

It’s a cabin made of horizontal timbers so unfortunately I don’t have stud walls to put celotex into. 

casper_gutman

If it's a log cabin-type structure then the timbers internally are usually meant to be left exposed, and look pretty similar to tongue and groove boards anyway, albeit horizontal not vertical. Mine is unlined - I just used a tinted hard wax oil as a finish on the timber.

If you want a 'cleaner' look inside then could you line it with insulated plasterboard? If you used, say, 22mm thick stuff then the increase in thickness over 8mm T&G plus 4mm Thermawrap would only be an extra 10mm, so might be manageable?

Elmroad82

casper_gutman said:

If it's a log cabin-type structure then the timbers internally are usually meant to be left exposed, and look pretty similar to tongue and groove boards anyway, albeit horizontal not vertical. Mine is unlined - I just used a tinted hard wax oil as a finish on the timber.

If you want a 'cleaner' look inside then could you line it with insulated plasterboard? If you used, say, 22mm thick stuff then the increase in thickness over 8mm T&G plus 4mm Thermawrap would only be an extra 10mm, so might be manageable?

Thanks! Maybe I won’t bother with the thermawrap will only make a neglible difference. 
Did you put in a dpm? And are 18mm floorboards sufficient would you say?

casper_gutman

I didn't include a DPM as such, but the whole cabin is built on a frame that's supported above ground on concreted-in recycled plastic posts. No damp is making its way up those bad boys! If it was resting on a slab I'd certainly include a DPM.

The 18mm floorboards have been fine. They rest on the supplied 50mm bearers on top of the joists of the base frame. I insulated between the bearers with 50mm Celotex. A greater thickness would have been better but this was a convenient choice as it matches the bearers and leaves the floor at the right height for the door etc.