I just bought a house from the 1960s in the Northeast and realized that it has barely any insulation left. I've received a quote for spray foam insulation at R21, which is 3 inches thick, for my attic (the roofline is 34ft x 20ft and the attic floor is 26ft x 20ft). My contractor suggests that I should close up the two gable vents on opposite ends of the attic; one of them has an electric fan that kicks in based on temperature. He says that with closed-cell spray foam, there's no need for attic ventilation because it prevents moisture and vapor, thus stopping any mold growth. However, I've never heard of this before. Is this legit?
5 Answers
Yeah, modern homes often use closed-cell foam without venting, but that usually means they have more insulation than just R21. For instance, in Texas, my in-laws' attic only gets 10 degrees hotter than their house, even in extreme heat, and it stays clean for storage, which is a huge plus! Just be sure to check what's recommended for your specific climate.
I totally get your concern—I've got a similar setup in my 1967 brick ranch home with plenty of ventilation. I'm honestly not sure how effective spray foam will be in keeping my attic cool in the summer heat when run alongside my AC. It makes sense about the moisture, but could sealing off the vents lead to rising cooling costs?
Close your gable vents if you have proper ridge and soffit vents. Gable vents are considered pretty outdated now. Think about it like this: it's like poking holes in a straw and trying to drink; it's just disruptive to the airflow. I recently had my gable vents sealed because of this very reason.
It really depends on where you're applying the spray foam. If you're insulating the roof rafters, sealing the vents is crucial; otherwise, the insulation won't be effective. However, if you're just insulating the attic floor, you'll need to keep the vents open for moisture control. Also, R21 isn't sufficient for your climate, where you might need between R49 and R60 to effectively manage both heat and moisture. If you're planning to spray both the roof and the floor, it could end up being redundant and wasteful.
I think that's misguided advice. Not venting your attic can lead to overheating, and that might ruin the effectiveness of the insulation and even reduce the lifespan of your shingles. I’ve researched this, and I came across reasons suggesting that sealing an attic doesn’t significantly impact shingle life if done correctly.
Definitely do more research. Depending on your local regulations and climate, the moisture control aspect could be different. It’s always better to be informed before making changes.
That’s interesting! I read similar things that backed up the contractor's stance on vapor and moisture control. However, it’s good to be cautious. Maybe I should look deeper into the pros and cons before making any decisions.