Insulating an attic ceiling
As mentioned in a prior post, I am looking at getting a heat pump installed in my house. Although I have been trying to get the heat pump contractors to put the air handler/ducts inside the finished space (we have a centrally located closet we can sacrifice), the vendors we have had out so far are only interested in putting them in the attic. We have another heat pump vendor coming out this week, but assuming he is singing the same tune as the last guy, I am thinking about what it would take to insulate the attic rafters and gable walls so as to keep the hvac equipment inside the building envelope. Also, I could see us maybe wanting to finish the attic to add two bedrooms sometime in the future, so if we did that, we’d have to do this insulation at that point anyways.
I live in eastern PA, right at the border of climate zones 4a and 5a.
From doing some reading on this site over the weekend, it seems like the basic options are:
1. Leave a vented channel from the soffit to ridge vent, then put fiberglass or cellulose insulation beneath that.
2. Spray foam the rafters and underside of the roof, with additional fiberglass/cellulose insulation underneath that.
I had an insulation contractor at my house Friday who offered to put fiberglass batts in the rafters, but he didn’t mention anything about a vented channel. Also, even if I did have a vented channel, with fiberglass underneath it, I have a hard time believing that would prevent air infiltration into the attic, without some type of membrane or other barrier at the bottom of the vented channel. Does that seem like a reasonable concern?
Regarding spray foam, I am turned off by the high gwp of cc foams, plus the general toxicity level of them.
In this application, it sounds like I could use open cell foam, followed by a fire barrier, followed by additional fiberglass/cellulose insulation? Does that seem reasonable?
Are there other options that don’t involve spray foam but are easier to install correctly (for air infiltration prevention) than fiberglass batts?
Could I just put polyiso or eps boards inbetween the rafters, or is the thought that you will never get that close enough to the underside of the roof to prevent there being a space for air/moisture to get trapped?
Could I do the boards between the rafters approach but leave a vented channel?
I have another insulation contractor coming tomorrow – any thoughts are appreciated.
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