Garden Studio Insulation

[edphill]

Hello All,

First post but have found the advice here useful hundreds of times before - so Thank You all for keeping up such a great service.

We would like to build an office in the garden and I am wondering about insulation to go between the walls (ceiling and floor sorted mostly).

I was wondering if anyone has any experience of using Triso or similar foil insulation between the walls? The construction would be - 44mm Shiplap, breather membrane, 50mm stud, 30mm Triso (or equivalent), vapour barrier, and then 12.5mm plasterboard.

I am hoping this will achieve around 0.3 U-Value but everyone only seems to recommend Triso for roof applications.

The problem is that the base (already there) for the office is only 10' x 8' (3m x 2.5m) and I would like to keep the wall thickness to a minimum to maximise internal space.

Any help much appreciated.

Thank you.

 

[mointainwalker]

I have no faith in tri-Iso as insulation however the point I have to make is that it is pointless to have a vapour-barrier as well as tri-iso as that is impermeable if properly taped.

T-I is generally only accepted ( don't know if I would say recommended ) in conjunction with traditional types of insulation to achieve specific insulation values.

 

[edphill]

Good point about the impermeable nature of the product, thank you. I would still need the vapour barrier between the stud and shiplap though to prevent moisture from the outside permeating. May I ask why you don't have faith in the product? I would be interested to hear your views.

Thank you.

 

[mointainwalker]

Multi-foils as they are generically called are rather controversial as their claims for insulation efficiency cannot be verified by the standard test-method which is called the "hot-box".

When tested this way, the results are only about 35% of what is claimed. T-I's response to this ( since they were the first producer) was " ah, but it doesn't work like traditional insulation so you can't test it the same way."

It is now accepted by some (?) BCO's but only in combination with traditional materials which seems to confirm that it doesn't do what it claims.

The other thing I don't like is what I saw as their deliberately deceptive advertising. They used to claim something like :

".... same insulation value as 200 mm of fibre-wool but only 30 mm thick.."

Even leaving aside the disputed efficiency the above is a lie because as their installation methods state, it is essential to have an air-gap of 25 mm on each side of the foil, so the real installed thickness is not 30 mm ( the foil ) but 25 mm (air) + 30 mm (foil) + 25 mm air).

Total obviously 80 mm and not the 30 mm they boast about.

Since T-I is now producing ( or marketing at least) compressed wood-fibre as an alternative to other traditional insulation materials, I take this to indicate that they accept that multi-foil will not wipe-out trad materials, which it would if their claims were widely accepted.

I would still need the vapour barrier between the stud and shiplap though to prevent moisture from the outside permeating

.

I don't think so. You are proposing a breathable membrane which should stop water ingress and it is normal to allow the wall on the cold side of the insulation to breathe.

 

[edphill]

I think those initial problems will stick in everyone's mind for a very long time.

I have just done some reading around the subject and there are problems with not meeting the Hot box tests, but as Triso said - it really doesn't work that way.

It's all about the air gap which allows heat to turn into radiant heat which is then reflected. If the surfaces are touching then the heat travels through the material.

However, SuperFOIL is tested and certified to BRE443 Part ‘L’ of Building Regulations for Foil Insulation using the conventional ‘hot box’ test method. Which is good news.

You do make a very valid point about the 80mm though. Maybe I am just better off sticking 80mm of Celotex in there and having done with it?

Thanks for your help.