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We are adding on above our garage to expand our master bath and closet area - total size is approx 10'x20'.

With unheated space below, we want to ensure we keep temps bearable in this new space. Architect listed I think R-38 in the ceiling and floors, but with 2x4 framing for the walls, R-15 in there.

I was wondering if anyone has had a similar addition and can comment on the comfort level in that space. It isn't too late to change the framing to 2x6 or have foam insulation instead, but neither are inexpensive upgrades.

I'm located in NJ if that helps with recommendations.
 

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retired framer
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We don't build any living space with less than 2x6 exterior walls. .
 

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A common issue with living space over an unheated garage is air leakage. If you go crazy with caulking and seal drywall to framing and all framing seams half the battle is won. The other half is insulation and assuming you have 2x10 joists below getting the r-38 is a stretch. If you need the full r-38 you may need to use mineral wool or high density fiberglass. Mineral wool would be my choice. You need an r-value around 4.1 per inch assuming 9.25" joists.

Bud
 

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Our bedroom is above the garage, we used open cell spray foam in the floor. If I were to do it again, I would use closed cell foam in the floor for a few inches followed by fiberglass or mineral wool.

Walls, I dunno. we have R15 in the wall fiberglass. its OK. but I might consider 2x6 framing if it weren't too expensive. Honestly, the floor is the key.

We're OK in our room though could be slightly better. The part that gets cold is the 2' cantilever certain areas of the house. that is open cell foam, and I think we should have used closed cell. We're on Long Island
 

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I would not upgrade the walls. Most of the heat loss is through the ceiling, you got that covered. What is left is mostly loss through air infiltration. Seal it up and don’t cut corners with cheap windows. With R15 walls, a few more R won’t make much difference.
I have found that it helps if there is a little airspace between the insulation and subfloor.
 

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On a 10 X 20' addition, the cost is minimal to switch to 2 X 6 framing.
It is unlikely anything is built with 2 X 4's anymore except interior walls, garages and sheds.
Whatever you pay for in additional materials will be re-couped in energy savings.
And you actually lose more heat through the walls than the roof....about 35%.
 

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retired framer
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On a 10 X 20' addition, the cost is minimal to switch to 2 X 6 framing.
It is unlikely anything is built with 2 X 4's anymore except interior walls, garages and sheds.
Whatever you pay for in additional materials will be re-couped in energy savings.
And you actually lose more heat through the walls than the roof....about 35%.
It is likely only 3 walls too.
 

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retired framer
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I would not upgrade the walls. Most of the heat loss is through the ceiling, you got that covered. What is left is mostly loss through air infiltration. Seal it up and don’t cut corners with cheap windows. With R15 walls, a few more R won’t make much difference.
I have found that it helps if there is a little airspace between the insulation and subfloor.
It is that extra little bit of R you get from the 2" of wood that prevents ghosting on the interior of the wall. :wink2:
 

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On a 10 X 20' addition, the cost is minimal to switch to 2 X 6 framing.
It is unlikely anything is built with 2 X 4's anymore except interior walls, garages and sheds.
Whatever you pay for in additional materials will be re-couped in energy savings.
And you actually lose more heat through the walls than the roof....about 35%.
Maybe by you, but i can tell you the 2x4 lives on up here in NY. not saying its not worth doing 2x6, but that by me, most seems to be 2x4
 

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Would 2x4's with 2" of continuous exterior insulation be better off insulation wise than 2x6's without exterior insulation?


Also, isn't it code everywhere now to have exterior insulation?
 

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Where are you in terms of climate and code requirements?
Does this new space have 8' vertical walls or is there a sloped roof involved?
10' x 20' sounds like a space taken from a sloped attic so there are other issues that need to be covered.

Tell us more about what this looks like.

Bud
 

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retired framer
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Would 2x4's with 2" of continuous exterior insulation be better off insulation wise than 2x6's without exterior insulation?


Also, isn't it code everywhere now to have exterior insulation?
Not yet.
 

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retired framer
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Where are you in terms of climate and code requirements?
Does this new space have 8' vertical walls or is there a sloped roof involved?
10' x 20' sounds like a space taken from a sloped attic so there are other issues that need to be covered.

Tell us more about what this looks like.

Bud
To me, it sounds like a roof off addition, if it was trusses you can lift the roof off and reuse it. With a big enough crane.
 
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