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Thread: Garage insulation - opinions needed

  1. #1
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    Default Garage insulation - opinions needed

    Opinions needed please....

    I am doing a new build...I have a 30x40 attached garage (only 13' of shared wall with the house though) with a 30x40 full story above it, to be used as a workshop. Garage will be insulated with fiberglass in the walls....I believe he is doing R-13, but potentially could be R-19. I'll have to ask.

    My plan is to install a minisplit in the workshop area. The actual garage area will be unheated - I'll just use a space heater or something when needed. For the workshop, I just want to keep the humidity out in the summer and drop the temp a little, and keep it at 55-60 in there in the winter. Basically, to make it tolerable to be in there.

    I don't ever expect to finish the workshop space for liveable area, but I always liked that I have 1200 sq ft available as an option in case I need it for elderly parents, kids that move back in someday (they are 4 and 7 now), etc.

    Builder normally puts in R-19 in a garage ceiling, so that is included in my base price. He can put R-30 fiberglass in the garage ceiling (so, between the garage and workshop) for ~$300 as an upcharge. That is a no-brainer. I will at least do that.

    The house is actually being spray foamed, and I can have them spray foam the space to R-30 (again, garage ceiling/workshop floor joists area) for $3500.

    I completely understand the cost - it's a big area. That being said, it's a lot of cost. Do you feel that in the floor of the workshop, R-30 fiberglass would do just fine, or would you cough up the $3500 to have it foamed. Is it really worth it?

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    For a little bit of added sound barrier along with the insulation benefits it might provide, i would have it done.

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    I didn't insulate my garage at all when I built it. I figured I wouldn't be out there in the winter so I wasn't too worried about it. And it hasn't bothered me the times I had to change my oil in January or stuff like that. The thing I have learned, though, is that it gets to almost 100 degree in there in the summer. You need to keep a good seal between the area you park/work in and the roof vent area. I would think R-30 would be fine if you are not heating or cooling it. I have to get mine drywalled now so that the shredded newspaper spray in guy can come out. I looked at doing the pink type stuff and it would super expensive.

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    I should clarify - the 2nd story, over the garage, is a workshop. It's not part of the house. So, noise is a non-issue. I am wondering if it's worth $3500 to go from fiberglass to foam in the floor of that workshop - unheated garage is below it.

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    The only downsides I can see are the upfront costs, & if later on you need to run-repair any wiring/plumbing/duct in those cavities...

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    What is the R-value of the spray foam?

    I have an attached garage with no attic so it vented to the outside and was not insulated. Its 2x4 construction. I installed an insulated garage door and that helped a ton. This summer I built a drop in the ceiling and ran plastic soffit vents to the roof vents. The walls are R13 and the ceiling is R30. It stays about 30 degrees cooler in the summer than it did, humidity is lower. I am waiting to see how this winter goes. I have an electric DeLonge oil filled radiant heater that did ok thru last winter (with the heat being vented straight to the outside) so this year it should be pretty nice.

    If I were in your situation I would possibly do the fiberglass batts rolls of R13/R19/R30 now and if you decide that it wasnt great, then cough up the $3500 later (dont drywall anything until you make your mind up, if its not too late)

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    I would be the same - R30 - but R values seem to be BS when comparing the two products. The real advantage of the foam is it's a vapor barrier too - theoretically the same R-value but foam performs much better, especially in very cold environments.

    At the end of the day, though, is that advantage worth $3500 given the planned usage of the space?

    He would be drywalling, and honestly, I'd rather it be drywalled now instead of doing it later. I am thinking I'll go with R-19 in the walls (he just confirmed that's what he does as a standard) with R-30 in the ceiling. I think that'll give me a very nice garage space, and I think it sets me up well for the workshop above it.

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    Club Member mustangmike6996's Avatar
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    Quote Originally Posted by Atrus View Post
    I would be the same - R30 - but R values seem to be BS when comparing the two products. The real advantage of the foam is it's a vapor barrier too - theoretically the same R-value but foam performs much better, especially in very cold environments.

    At the end of the day, though, is that advantage worth $3500 given the planned usage of the space?

    He would be drywalling, and honestly, I'd rather it be drywalled now instead of doing it later. I am thinking I'll go with R-19 in the walls (he just confirmed that's what he does as a standard) with R-30 in the ceiling. I think that'll give me a very nice garage space, and I think it sets me up well for the workshop above it.

    If it is just a workspace, I think you can get away without the vapor barrier, but don't run cars for a long time. Maybe add an exhaust fan if you are running it with the doors closed.

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    Club Member my89notchback's Avatar
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    Do an insulated door or doors too. I had to insulate mine on my own. You loose a ton thru the door.

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    Personally, I'd spend the $3500 and spray foam the garage ceiling now. 1) You're probably getting a slight discount on it since the contractor is already onsite doing the house.... vs. waiting 5-10 years and calling that same contractor back to just to do the garage ceiling as a standalone job. 2) It sounds like the probability of the upstairs turning into an apartment is pretty good. Spray foam will provide the necessary air barrier between the garage and apartment. Fiberglass batts, regardless of R-value, will not stop air leakage. I'd spray foam it and drywall/tape everything... and be done with it.

    With all of the stuff that's in a typical garage -- carbon monoxide, fuel vapors, landscaping chemicals, etc. etc. -- I wouldn't think twice. If $3500 is too much, have them spray 1" across everything... and then back fill it with fiberglass.

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