Q&A OF THE WEEK: “Is It Okay to Make a Vented Attic Unvented?”

Q: Is it wise to remove attic insulation and replace it with spray foam on the underside of roof sheathing? My brother recently moved from a cold climate to Florida and had all the attic batt insulation taken out. Vents were plugged and spray foam applied to the underside of the roof sheathing. This reduced attic temps to within 5ºC of his house temperature and lowered the air conditioning load. Is this a good strategy in both cold and hot climates?

Vented attics like this one cannot easily be changed to an unvented version. Having a cool attic in summer is a good goal, but there are better ways of making it happen than creating an unvented attic in a home that wasn’t designed for it.

A: I’m not crazy about this approach for a couple of reasons. Considering the trouble of removing and disposing of the old and perfectly good insulation, and the expense of applying spray foam (quite costly), the pay-off doesn’t seem to be there. Yes, an attic will be cooler this way, and this will reduce air conditioning costs. But for most situations you can accomplish the same thing with an electric attic fan. They’re thermostatically controlled and do a great job moving hot attic air outside. With a fully sealed attic like your brother now has, issues with stagnant air and moisture build up can occur. Imagine what will happen in your brother’s  hermetically sealed attic if his roof ever leaks. There’s no place for the moisture to go, so it will sit there and fester, triggering mold and rot. Attic fans, by contrast, in a ventilated attic, ensure there’s never any stale air, dampness or condensation building up.

On a related note, traditional organic asphalt shingles will curl and fail quickly over an unvented roof like your brother has now. The reason is heat. With spray foam insulation applied to the underside of the roof sheathing, the roof surface will get exceptionally hot in summer. This is no problem with fibreglass shingles in this situation, but traditional organic asphalt simply can’t take the heat. Do you know what kind of roof your brother has? If it’s organic shingles they probably won’t last five years even if they’re brand new now.

All this said, I’m a big fan of under-roof insulation, but only when it’s part of a larger plan to create a livable attic that can be ventilated by opening windows or skylights.. So many homes could have so much more living space if the area under a roof was finished and insulated. I don’t see the value in insulating the underside of a roof if the attic remains unliveable.

More homes should have liveable attics. Click here for an overview of the attic-finishing process.

 

Learn More Every Saturday!

FREE weekly tips and advice to make your home work better, whether it’s a rural homestead or a place in the city.

Your subscription could not be saved. Please try again.
Your subscription has been successful.

Just want to say how much I enjoy your Saturday morning newsletters and website. The content is always excellent... - FL

Thanks so much for the terrific work you do, and the outstanding resource you provide. - KS

Your videos are outstanding! Very instructive, and animations and your speech really helps to get the messages! - DB

Baileylineroad is supported in part by advertising. If you can't see the ads below, please consider turning off your ad blocker when visiting our site, or subscribing to our newsletter. Thanks for visiting!
1 Shares
Tweet
Share
Share
Pin1