Improving attic insulation in 1.5 story Cape
I just bought a Cape in zone 5A in NH which has two rooms upstairs, splitting the attic into three zones. The side attics, and the space above the rooms. The space above the rooms is vented with gable vents on the ends and a continuous ridge vent. The side attics are my concern. One side appears to be completely sealed, and has ‘balsam wool’ insulation in the rafters, completely filling the rafter depth. It seems to be in decent shape but there are some holes and insulation falling out here and there. Under the floor boards there are some batts but the coverage isn’t perfect.
My initial thought was that I would just blow in AttiCat on the floor, but now after reading tons of material on the internet and know this is an unvented attic space I see that this isn’t going to do much. I have seen tons of contradicting information about vented vs unvented. Some people claiming unvented is bad, others say it’s great, etc etc. I had considered converting to vented, but in the one side attics the roof joins with the roof of a 3 season porch, so that complicates adding soffit venting I would imagine.
So, my research leads me to believe that removing the balsam wool and spraying closed cell foam would be an improvement. I have seen people talk about using baffles or 1x1s and thin plywood to create air channels under the roof deck also. I’m not sure if this is worth the effort if I have no way to get soffit vents connected to the channels? My other concern is the spray foam would be much more expensive than blow-in on the floor.
My question is, would it be a bad idea to to a 1-2 inch layer of closed cell foam, use some furring to increase rafter depth, then some sort of fabric or netting, or perhaps even rigid foam and blowing in AttiCat or cellulose in that space? In my mind you’d have the vapor and air barrier of the foam, and increase your R value with the blow in… all at a much cheaper cost…. but is there an issue with moisture/condensation or some other issue with this layering? I would then use more blow-in in the vented attic space above the rooms (on the floor of course).
Secondly would I want to put any kind of insulation behind the kneewalls?
Perhaps I would be better served to just do the blow-in above the rooms, and the other side attic (which I believe is vented, has no balsam wool, but I need to check it out further), and spray foam the rim joint of my basement for now?
Thanks in advance for opinions and suggestions!
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