Its raining in my attic!!

Not enough insulation depth to stop condensation from forming on the surface of this spray foam roof line. The BER does not recommend installing a flash and batt attic roof installation unless you install enough spray foam to ensure that the surface temperature of the insulation does not drop below the dewpoint temperature of the warm, humid inside air. Also, the surface texture of the insulation will not allow the batt insulation to maintain complete contact with the spray foam, rendering the batt insulation an R-value of close to zero. Not to mention that gravity will eventually pull the insulation down and away from the roof deck in any case. It only takes a small air space to completely devalue the batt insulation. We recommend either spraying the full IECC code required R-value depth in the roof deck, or a flash and net/spray in place fiber or cellulose insulation that is fully supported with rigid backing so it does not sag and separate from the spray foam surface. In any case, the spray foam should be at a sufficient depth to ensure no condensation will form on its own, regardless of what additional insulation you install beneath it.

Views: 338

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Bud Poll replied to randy tolowski's discussion Another unvented roof question
"I've removed caulking that was over 30 years old and it outlasted the materials to which it…"
10 hours ago
Profile IconAmanda Hallock, Kalvis, Tyler Grubbs and 6 more joined Home Energy Pros
12 hours ago
Corbett Lunsford posted videos
13 hours ago
Sean Lintow Sr replied to randy tolowski's discussion Another unvented roof question
14 hours ago
randy tolowski posted discussions
16 hours ago
Todd Collins replied to Tom Strumolo's discussion Ancient (70's) wall foam insulation, now a powder.
"What did you find about the dust?  "
20 hours ago
Susan E. Buchan commented on Shawna Henderson's blog post Drainwater Heat Recovery Units & Water Efficiency
"Makes sense, Shawna. Thanks"
20 hours ago
Shawna Henderson commented on Shawna Henderson's blog post Drainwater Heat Recovery Units & Water Efficiency
"Susan, I'm not sure that insulation on the unit would be of great benefit, as the drainwater…"
20 hours ago

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service