I'm planning to spray foam my attic and could really use some advice. I live in a zone 4A, 1979-built house with a vented attic that's currently covered with fiberglass insulation. I dislike the fiberglass and would prefer to apply spray foam at the ceiling to make DIY projects on the attic floor easier. My attic has soffit and gable vents, but no ridge vent, exhaust fan, or windows. A contractor will handle the installation, which involves removing existing insulation, applying 7" open cell Alpha Polymers spray foam to the roof deck, removing the whole house fan, dry walling, building up a gable internally, and cleaning up afterward. I need some clarity on a few things: How will off-gassing during the cure process be managed since the attic will be sealed? Should I keep all rooms closed? If I smell chemicals after 24 hours, is it smart to use a fan to vent the attic air out? Will I need a vapor retarder after curing? Should I consider adding passive grilles for air circulation? Given my area's extreme temperatures, would a dehumidifier be necessary? Lastly, I've heard the foam can off-gas again in hot weather—should I be worried about that?
2 Answers
To manage off-gassing, you might want to leave the attic windows open while the foam cures since it’ll be sealed otherwise. For your other questions, I kept my attic door closed and just opened the windows; it worked fine for me. If you smell chemicals after a day, it’s really up to your comfort level whether to vent. I didn’t smell anything bad after a week, but be mindful. As for the vapor retarder, using fireproof paint or drywall may be a requirement in your area. I didn’t add passive grilles, but it could help; I suggest checking local codes. For moisture, I installed a Wi-Fi humidity detector and learned mine rarely exceeded 55%, which is manageable. And yeah, I’ve read foam can off-gas again in the heat, but I personally didn’t have issues with it.
I appreciate the input! I'll be sure to stay on top of the humidity and smells during the process.
I've been thinking about this for ages too! If you're sensitive to smells or have kids, consider leaving the place for about a week. You might also want to think about closed-cell foam since it provides higher R-value in a thinner layer. If you're considering a dormer, it could give you extra space plus better ventilation, which would help with humidity build-up. Be aware of your roof's lifespan, though—if you layer foam and then need a roof replacement soon, it might complicate things and cost more down the line.
Thanks for sharing your thoughts! My roof's in pretty good shape with at least 10 years left, but could I add a dormer after the foam is applied?
Good point about the roof! I hadn’t considered that; I’ll have to do some math on the timing.
Thanks for the insights! I actually forgot to mention that my attic has no windows, so I’ll have to keep that in mind when considering ventilation.