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Cape Cod home insulation, vented vs. unvented

cgmorgan | Posted in General Questions on

Hi all,

I’ve been reading through a lot of the posts and articles here and know this is a pretty common question, so I was hoping for some advice from those who know a little (a lot) more than me.

I recently purchased a 1950s Cape Cod style home in Quebec, which after a little inspection I realised had very poor insulation. Long story short the full second floor is now gutted, and I’m trying to figure out the best way to insulate it after a lot of back and forth with contractors and insulation companies.

My original plan was to add some furring strips overtop of the 2×5 beams, increase the depth to 5.5 inches, and spray from the soffit up to the peak of the roof. This would help me achieve around an R33, not ideal but the best I can get with the space I have. My contractor advised against creating a hot roof system, and said I should add the standard polystyrene baffle ventsĀ  coming up from the soffits, spray over them up to where the attic starts, and then drop 15 inches of fiberglass batt on the ceiling. I was hesitant as we would lose around an inch of space for insulation, which would drop me to R27, and was worried the vents would collapse under the pressure of the spray foam, but trusted his advice. After inspecting the soffits however we realised there were no vents and it was straight plywood all the way across, so it was a moot point anyway. He changed his mind and said we should spray directly onto the roof and place the fiberglass batts as before.

After 5 long weeks of cancellations, delays, changing companies, etc. the day (today) finally arrived where the company was going to come and spray. The guy was there for 1 minute before he looked at me and said he couldn’t in good conscience spray directly onto the roof. He regaled me with his stories of 15 years of experience of dealing with ice dams and stressed how important keeping the system ventilated was. He advised me to add vents to the soffits, use rigid foam on 1″ spacers for the baffle vents and spray over top of them. I was told no matter how thick the insulation was there would be heat transfer to the roof, and ice dams and water damage were inevitable.

Now I am stuck with a bit of a conundrum. Is he right, and I need to go through the incredibly labour intensive task of adding baffle vents to 35 rafter bays (after I already installed the furring strips for the gypse as I was told they were easy to spray around …) and modifying the soffits? It will be vented, but have a lower R value. Is he wrong, and 5.5 inches of spray foam directly onto the roof is the best approach, and I won’t have to worry about snow melting? If that’s the case, what about my contractor’s advise to do fiberglass in the attic instead of spraying all the way up? I mean, if there’s no air intake from the soffit vents, are my roof vents of any use?

I won’t lie, my preference is shooting directly onto the roof and calling it a day. It’s a little more expensive, but I find the idea of removing all of the furring strips, cutting rigid foam for 35 14′ long irregularly spaced rafter bays, sealing them, installing all of my soffit vents, etc. to more than outweigh the cost. That being said, if it’s the wrong approach I’d certainly rather do it correctly the first time.

Any advice, experience, or tips you could provide would be greatly appreciated. I’m happy to provide any more information or photos if it’s helpful.

Thank you.

GBA Prime

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