Radiant barrier spray paint vs. open-cell foam
MAY 14, 2010
3:20 PM EDT
Open-cell foam vs. spray applied radiant heat barrier (paint)
by J. Ingols
We have a 50 yr. old home with some floored storage in attic and worn out fiberglass insulation in unfloored area, no HVAC there but some duct work. Am trying to improve comfort level on top floor and reduce energy costs. Have had estimates to have radiant barrier paint and additional blown insulation added and had an estimate to have open cell foam (Demilec) applied and encapsulate the attic. The question is not only which makes the most sense to do, but if we do use the open cell foam there is a question as to whether the best choice is to spray directly on the roof decking or to do it with a baffle system that essentially leaves a breathing space around the entire encapsulated space and supposedly keeps my roof happier. Oh yeah…..then there is the vapor question!! I am so confused. Any advice? Thank you.
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Replies
J. Ingols,
If cost is not a factor, it makes more sense to insulate the roof plane so that you bring your attic (and the attic ductwork) into the conditioned space of your home.
"Radiant barrier paint" is a scam. No paint exists that meets the technical definition of a radiant barrier. Even if it did, its effects are small compared to insulation.
You can insulate your sloped ceiling with either open-cell or closed-cell spray foam; the installation can either include ventilation under the roof deck or have no ventilation. If the installers are conscientious and the specs are good, all of the above options can work well.
The higher the R-value, the better the job. Get the highest R-value you can afford. Beware: some spray foam contractors try to convince customers that spray foam can be installed with lower R-values than the minimum code requirement. Insist that your spray foam insulation at least meet the minimum R-value under your local building code.
Whatever you choose, be aware that studies in varied climate zones (both hot and cold) have demonstrated that a ventilated roof will be more durable than a "hot roof".
Why not use the radiant barrier product available in the roll form?
Dear HTTP,
Because the cost of any radiant barrier (especially in a retrofit application) is much higher than the cost of real insulation in terms of reduction in heat flow per dollar invested.