[Strawbale] bubble foil

[dfugler at cmhc-schl.gc.ca]

Good morning,

Regarding David Gray's suggestion to add an inch of bubble foil on the 
bottom of a crawl space insulation job: DON'T DO THIS!

There are two reasons why this is a bad idea. The first is that you are 
putting a vapour barrier on the cold side of the insulation. Ask Kim 
Thompson how her straw bale insulated crawl space floor worked when they 
covered it with polyethylene the first time. It leads to rot.

The second reason is that foil bubble wrap products are notorious for 
overstating their effectiveness. They have about R-1 or R-2 of insulation 
value, and I have seen claims up to R-14. Here is the proof of their 
insulating effectiveness (under slabs, but the research is still 
relevant):

http://www.cmhc-schl.gc.ca/odpub/pdf/63728.pdf

Build it right. Foil bubble wrap is the wrong product for this 
application.

Don Fugler
CMHC Policy and Research