Insulating Basement Garage with finished areas


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Old 10-02-15, 05:49 PM
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Insulating Basement Garage with finished areas

We have a 30x30 basement with a 16' wide garage door and garage 'space' that measures about 600' of the 900' basement. I've already spray foamed the rim joists and the two corners on either side of the garage door were there is 2x6 stick framing. Aside from the stick framed wall with the garage door, the majority of the other three walls is ICF at 11" and mostly built into the sloping ground around it. The floor joists above the garage for the main floor are 2x4 joists about 18-24" tall (vacation cabin and I'm not sure without measuring) and 16" apart.

While I'd like to spray foam the entire underside of the subfloor, I'm thinking that may not be the best idea. Without getting too complicated, the garage and stairway to the main living space from the garage is not currently separated well. My thoughts are to spray foam the underside of the subfloor above the garage space, then drywall the ceiling and floor joists to separate the garage from the stairway and the other finished space. It isn't ideal but the finished space is only accessible by going through the garage from the stairway. The garage will be separated from the stairs and the finished area with 2x6 walls that are going to be spray foamed with fire doors into the garage. I will also drywall the whole way through the floor joists (extra, probably not needed if garage is drywalled already but this will also add another layer between the spray foamed subfloor above the garage and the finished space.

Above the finished space, I'm not sure if I should leave the subfloor bare or spray foam the underside? I'm going to insulate the bottom of the floor joists/ceiling of the finished space with 1.5" thick foam board between joists followed by 2" foam board under the joists (ceiling of the room(s), then drywall. This will ensure the extra room, laundry, and bathroom are well insulated and separated from the garage but that leaves the subfloor 2 feet above on the top of the floor joists uninsulated which is where the water lines run. The heat would still be able to flow down through the floor.

If I spray foam the whole subfloor, then add foam board on the bottom of the floor joists, I believe I'll essentially create an enclosed space within the floor joists above the 300' of finished space.

Thank you in advance for your thoughts on this.
 
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Old 10-03-15, 04:08 AM
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The floor joists above the garage for the main floor are 2x4 joists about 18-24" tall.
I think that you meant studs not joists.

Is there a problem with the heat, in the winter, that you want to add all that insulation? For example, is the heating uneven? Do you have a hot water system, steam or forced air? Is it oil or gas?
 
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Old 10-03-15, 09:18 AM
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The floor joists are 2x4 construction joists.

The entire cabin is electric heat. The main reasons for wanting to add spray foam to the underside of the subfloor are cold floor and air seal from garage below. The reason for wanting to add foam board above the area we will finish off in the basement garage is to add an air seal like the main level as well as keep the electric heat in as the rest of the basement/garage will be much colder.
 
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Old 10-03-15, 04:50 PM
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With electric heat, I can understand why you want to insulate. I don't know enough about spray foam insulation, to comment on it. Maybe someone else can advise you as to which insulation is best.
 
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Old 10-03-15, 07:56 PM
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We do have a wood stove on the main floor in the living room. Once we get it really hot and turn on the ceiling fans to circulate the air, it can actually get a little too warm. Most of our weekends are pretty short though so we rely on the electric heat when we show up for the first night.
 
 

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