On 24 Jul, 13:15, JP Coetzee wrote:
I have a new 20'x7' shed which my wife will use as an artist's studio.
The shed is heavy duty T+G. I want to insulate the walls and roof.

My local Sheffield Insulation trade Counter recommends new-fangled
stuff called "Frame Foil" stapled onto the uprights of the shed walls,

It's all surprisingly expensive. You need to learn what R,K & U values
are about, then run the numbers (simple spreadsheet) to make any sense
at all. Watch out, as most things are listed (on the web anyway) in US
units for R value. Also look at finished costs, including battens,
membranes and plasterboard.

K is an inherent property of the material. R is the overall
performance of a wall component (one material layer), taking into
account its thickness. You can get total wall performance by adding up
the R for each layer (Big R is good). To a rough approximation, R for
bulk materials (glasswool) is their thickness divided by their K. U
is the reciprocal of R and you might see building standards for
finished wall expressed in it (little U is good).

If you use SI units, that's it. If you use US units, there are screwy
conversion factors everywhere.

For a material like Frame Foil or plasterboard that only comes in
"finished thickness", then there's no K value, just one overall R.

Frame foil is deliberately designed to have an R value about the same
as 150mm glasswool, a "typical" insulation level for walls.

What's good about it?

* Thin. It's about 65mm thick overall - inch for the foil layer, 3/4"
airgap either side. You _must_ preserve this airgap!

* Built in vapour membrane.

* Easy to install. Not so much bulk to worry about.

* Resistant to cold bridging. You can squash it narrow without loosing
too much performance and you can squash it entirely flat and still
have a little. Compare this to glasswool against a stud where it tips
away a little and leaves a gaping gap.

* Easy to install, especially on walls.

What's bad?

* Performance isn't quite as good as a really thick glasswool layer.

* Easy to screw up the installation. Squashing it or not providing the
airgap (use counterbattens before plasterboarding over it!) will
produce a poorly performing wall.

* Easily confused with "bubble" foils that only have about half of the
R performance.

* Bad reputation with some regulatory bodies, owing to inept testing
methods a few years ago. Lots of people will tell you "it doesn't
work".

* Cost.


About the best (practical) insulation / thickness performance is from
Cellotex etc. yellow foam rigid boards with isocyanate foam and silver
foil faces. These are 65mm too, about the same as Frame Foil.

Cheapest (and perfectly good) is rockwool or glasswool of 150mm or so.
Somewhat more labour to fit and it's two or three times thicker, which
can be an issue for headroom in some retrofit locations.

Your price appears to be roughly £10/m^2, which is slightly more than
glasswool (by the time you've put plasterboard over it). Yellow foam
is more than this, maybe £15-20 / m^2 and the bubble stuff is half
this, maybe £5/m^2.

I use the foil on walls, because the ease of installation is useful.
If I don't care about thickness, I'd go with glasswool. For retrofit
insulation I'd look at the yellow foams, which I don't otherwise like
owing to price and chemistry.