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Discussion Starter · #1 ·
Hey all I just recently bought a 1947 cape in NJ climate zone 4. I'm unsure the best way to go about insulating the attic space. Currently it has two gable vents and a ridge vent, There is no soffit vents.
The upstairs room also has knee walls and a collar attic. I'm looking for the best way to go about insulating the whole are including behind the knee walls because I have my central air unit in one of them which would be why I want it to be conditioned space. Also rafters are 2x6. I'm looking for the best way to do this. TIA.
 

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If I'm understanding right, you want the entire attic, including the collar attic, to be in the conditioned space, right? When I was considering attic insulation options, one of them was to bring the attic into conditioned space. The recommended approach was to use spray foam insulation under the roof deck and on the gable walls. You'd of course also have to seal the gable and ridge vents. But spray foam has its problems. Look up "hot roof" - apparently not all shingles are designed to be placed on insulated roofs. And then there's the fact that spray foam is toxic, flammable and not very environmentally friendly.

The attic I was dealing with already had fiberglass batts under the roof deck, on the gable walls, and on the attic floor. It also had only one gable vent and no other ventilation. It made absolutely no sense, and sure enough, the roof deck was rotting in parts due to the poor ventilation, and the decking had to be replaced when I re-did the roof. I also have a central a/c air handler in that attic, so like you I also thought I could bring the attic into enclosed space. But the a/c unit is also a gas furnace and that would have required a source of combustion air. And I didn't want to deal with spray foam. So I had the roofers install a ridge vent and soffit vents, had the fiberglass insulation under the roof deck removed, and installed blown-in cellulose on the attic floor. A year later it all seems to be working well. The a/c probably does work harder in summer than if it were in conditioned space, but at least the ducts got buried under blown-in insulation.

Maybe one option for you would be to close off the part of the attic where the a/c is and bring that into conditioned space, and insulate the rest of the attic conventionally.
 

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Since we can not see your structure. I suggest that you call some insulation contractors and have them give you some bids. They should be able to point out specifically what we can not see.
 

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Discussion Starter · #4 ·
If I'm understanding right, you want the entire attic, including the collar attic, to be in the conditioned space, right? When I was considering attic insulation options, one of them was to bring the attic into conditioned space. The recommended approach was to use spray foam insulation under the roof deck and on the gable walls. You'd of course also have to seal the gable and ridge vents. But spray foam has its problems. Look up "hot roof" - apparently not all shingles are designed to be placed on insulated roofs. And then there's the fact that spray foam is toxic, flammable and not very environmentally friendly.

The attic I was dealing with already had fiberglass batts under the roof deck, on the gable walls, and on the attic floor. It also had only one gable vent and no other ventilation. It made absolutely no sense, and sure enough, the roof deck was rotting in parts due to the poor ventilation, and the decking had to be replaced when I re-did the roof. I also have a central a/c air handler in that attic, so like you I also thought I could bring the attic into enclosed space. But the a/c unit is also a gas furnace and that would have required a source of combustion air. And I didn't want to deal with spray foam. So I had the roofers install a ridge vent and soffit vents, had the fiberglass insulation under the roof deck removed, and installed blown-in cellulose on the attic floor. A year later it all seems to be working well. The a/c probably does work harder in summer than if it were in conditioned space, but at least the ducts got buried under blown-in insulation.

Maybe one option for you would be to close off the part of the attic where the a/c is and bring that into conditioned space, and insulate the rest of the attic conventionally.
Yes you understood exactly. I did look up hot roof which is where i started to get torn. The previous owner had insulated a lot and I can defiantly see issue with the shingles it those areas. My only other thought was to have a roofer do 4in. rigid foam on the roof deck after removing the shingles then shingle over that.
 
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