Insulating a roof above the garage

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Old 03-17-19, 01:30 PM
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Insulating a roof above the garage

We are looking at buying a house, this house has a room above an un-insulated garage. The room has a slanted roof. The supports are what looks to be 4x10's or 4x8's. I don't yet know if there's a ridge line vent either. The soffits are vented and air does come up through them.

We obviously want to maximize the space. This house is in Maine. Should I leave a vapor barrier (1"~) from the soffit up to the ridge vent if it exists? What's the best way to insulate this? I will not be using spray foam. The room would be heated with a propane wall-heater.

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Old 03-17-19, 03:23 PM
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Converting attic space to living space is a common topic, but before you buy you need to determine if in this case it would be allowed. There are height and structural requirements that only your local building department will know. Maine has adopted a state wide building code as a minimum. They initially exempted smaller communities but not sure if that still applies.

There is also an allowance for a limited sloped ceiling area to use slightly less insulation. Of course more is always better but finishing an attic like this doesn't give you a lot of extra space.

Check your local building department for guidance before you buy. Don't consider that as valuable extra space if it can only be storage.

Bud
 
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Old 03-17-19, 05:32 PM
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It will be used as a photo studio. I will check with codes but am more interested in how to best insulate at this point.
 
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Old 03-17-19, 08:16 PM
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You will need to check what is in place for ceiling joists forming the floor of your new space. Their load capacity and the support below will tell you if more is needed.

Codes will usually ignore your intended use and assume you or someone in the future will be living up there. Thus access and egress will have to meet their standards. That is a local decision.

Insulating the slopes is the easy part. Determine the required R-value and select the insulation you want to use. Then build down the existing rafters to accommodate that amount of insulation plus the recommended 2" air gap.

Assuming side attic spaces you select one of the two options shown in the link below.

With the floor potentially moving up to meet load requirements and the rafters moving down to meet insulation needs the resulting headroom may be insufficient. Electrical and heat will need to be extended to this space and the ceiling and walls in the garage below will need to meet fire codes. Access from the garage will also need to be fire code approved.

I'm not trying to be a pain just preparing you.

Bud
https://www.greenbuildingadvisor.com...hedral-ceiling

https://www.finehomebuilding.com/201...ttic-kneewalls
 
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Old 03-18-19, 06:45 AM
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It's not going to be a living space but a studio that is used a few times a week. The floor is supported by 2x10' that are resting on a large I-Beam.

I was planning on have an 1" to 1 1/2" air gap for the soffit vents to reach the ridge vent. I was going to install rigid foam board as that barrier instead of those flimsy baffles. As far as additional insulation, I wanted to either use R30 batting or add additional rigid foam boards but I'm not sure that will be enough R value. I can't really extend past the rafters as it will take away from the head space.

I'm going back and forth on whether or not to build up there, it's a great space but maybe it's best for unconditioned storage. There's a nice spot in the basement that they were starting to frame up and is already insulated with what looks to be 2" foil faced foam board behind the studs and the basement has a door that they could come in through.
 
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Old 03-18-19, 08:01 AM
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You have received excellent advice thus far. It is best as unconditioned storage. As bud already mentioned, you will have hurdles with your building dept. The biggest problem with finishing spaces like that is getting adequate insulation (and air sealing) while still maintaining the 2" minimum of ventilation. Plus propane heat is the worst possible choice as it puts huge volumes of moisture into the air. I have seen underinsulated cathedral ceilings with so much frost in them that it flooded the house in the spring when it all melted.
 
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