[Strawbale] Foil bubble wrap with an air space

[dfugler at cmhc-schl.gc.ca]

Shoddy et al,

That is correct: a horizontal reflective surface under an air space with 
the heat flow going down creates an R-value (when clean) of about R-5. If 
you install the foil bubble wrap on the underside of the floor, with a 
still air space, over an unheated crawl space, you might pick up a little 
more insulation than the R-1 or R-2 that the product typically provides. 
You still have the vapour barrier problem though, with the foil being on 
the wrong side of the assembly. Given that you want at least R-20 here in 
colder climates, I think that there are better designs around with fewer 
problems.

We recently received a letter here asking us to go after manufacturers or 
distributors who misrepresent the R-value of their product. Householders 
have believed the R-value advertising hype and have installed foil bubble 
wrap as the sole insulation in a wall or floor assembly. There are 
probably reasonable applications for these products, but the majority of 
what I hear about is misuse.

Don