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.
- 1using blown insulation
- 2installing soffit and ridge vents instead
- 3Getting multiple contractor quotes to compare prices and recommendations
- 4Watching instructional videos online to research a potential DIY approach
In their words
Unedited, most upvoted first, each linked to the thread it came from.
“When I brought this up to my roofer he recommenced i not foam the deck, because he has seen issue with repairs when they opened up the roof.”source ↗
“Don’t do it, you’ll hate your past self”source ↗
“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 ↗
Where this came up
People with this problem also raised
- 2Do I need a vapor barrier over rigid foam in a basement?
- 2Should I replace old asbestos-wrapped ductwork while walls are open?
- 8Do I need to caulk my new shower or was it left unfinished?
- 2Can you use fiberglass insulation in a basement after flooding?
- 2Can I insulate and finish basement walls if they get damp?
- 3Should I buy a house with conflicting roof damage reports?