Is spray foam insulation bad for a roof deck?
Contractors often advise against spray foam on roof decks because trapped moisture creates hidden rot and makes future roof repairs significantly harder. This conflict leaves homeowners struggling to weigh energy savings against the risk of expensive structural damage.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1using blown insulationDid this help you?
- 2installing soffit and ridge vents insteadDid this help you?
- 3Getting multiple contractor quotes to compare prices and recommendationsDid this help you?
- 4Watching instructional videos online to research a potential DIY approachDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Went up into the attic this weekend to chase a draft and found something I wasn't expecting—or maybe should have expected, given everything else in this house. There's basically no insulation up there.”source ↗
“Last winter our heating bills were brutal, and now I know why. The house can't hold heat to save its life. Upstairs bedrooms are always cold, and the upstairs hallway feels like a wind tunnel.”source ↗
“I've gotten two quotes so far. One company wants to blow in cellulose to about R-49 and air-seal the attic floor first. That quote came in around $2,800. The other company said I should do spray foam instead and quoted me $7,500.”source ↗
“I've also watched about six hours of YouTube videos and I'm half convinced I can just rent a blower and do the cellulose myself for maybe $800 in materials.”source ↗