Garage ceiling insulation - living space above

Discussion in 'Garages, Workshops & Tools' started by EricsZ28, Aug 31, 2009.

  1. EricsZ28

    EricsZ28 Veteran Member Lifetime Gold Member

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    I'm trying to decide how to insulate my garage ceiling which is under two bedrooms. We get into the low teens in the cold months. My garage ceiling had 3" of insulation in the 10" floor joist cavities - which has proven to be insufficient.

    To make matters more interesting, the vapor barrier was installed upside down (towards the garage) and I observed some mold in the insulation as I removed it last weekend.

    I want to put in R30 insulation (9.5" thick) - but I can't decide on faced (towards the upstairs floor) or unfaced. The garage will have 5/8 fire-code drywall installed over the insulation.

    Can anyone share any insights to help me out?
     
  2. Rick WI

    Rick WI Veteran Member

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    Although expensive the abolute best method is to have a contractor spray fill the cavities with two part foam. Second best option would be to insure all sources if air infiltration are sealed with caulk, then install faced insulation with the vapor barrier towards the heated side.
     
  3. hardline_42

    hardline_42 Veteran Member Lifetime Gold Member

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    You might not need to have any kind of facing on the insulation. The glue in the plywood of the subfloor above acts as a vapor barrier (if it has a perm rating of 1 or less). This would be your most cost effective approach. Spray insulation is hideously expensive, has flamability issues and will take years before the savings (if at all) over regular fiberglass batting is seen. Check with your local code on what the R-value requirement is for ATTICS, not floors. If you use 2 layers of unfaced high density R-22 batting (5" thk.) you can get a rating of R-44, which is the most you can get in a 10" space, AFAIK.
     
  4. EricsZ28

    EricsZ28 Veteran Member Lifetime Gold Member

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    Yeah, my subfloor is the plank style (pre-plywood). So I don't think it will be much help. The foam makes a lot of sense, but I don't have that kind of coin right now.

    Is there a "correct" way to install faced insulation from the bottom? Specifically, what would I do around the cross braces? I don't see much choice other than to slit the insulation - which adds even more seams to the vapor barrier. Installing it from the top (to avoid slitting the vapor barrier) is not an option.

    Also, what would "sources of air infiltration" include? Are we talking about exterior seams, or are we talking about every joint in ever floor board? Should I seal up (at least stuff some insulation) around where the plumbing comes through the subfloor?
     
  5. hardline_42

    hardline_42 Veteran Member Lifetime Gold Member

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    Assuming the spacing between the joists is 16" or so, you can just push the insulation into place and the facing flanges should hold it up until you cover it with the 5/8" rock. Foilf-faced would be a good idea to help reflect the heat back in. I hate dealing with that cross-bracing but I haven't found a way around it. You just have to trim the batts and cut pieces to fill the awkward spaces. Don't go crazy with the sealing. The idea is to trap some air between the two spaces, not make them airtight. Plumbing penetrations should be sealed, but the gaps between the planks will be covered by the facing and 10" of batting.
     
  6. Rick WI

    Rick WI Veteran Member

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    Yes, any seams or penetrations into the living space. Call an insulation contractor as you MAY be able to get some tax credits or incentives from your local utility for the foam work. Or at the very least have them foam just a small depth to seal the area rather than fill it complete. This type of area is just horrid for heat loss an I think it's worth a bit of time to research a bit.

    I don't know if there are options to spray a 2k type foam yourself, in other words rent equipment to do it. That might be another option that a home center like home depot might be able to help you out with.

    Working around the bracing is always an issue with batts. No easy solution, especially with the heated side on the top. No way to get a good seal with the vapor barrier. With that type of setup you may just want to go with unfaced batts and try to slit batts as little as possible to work around the bracing but making sure you have a tight friction like fit around the opening. Hard to explain but hopefully you get the idea.
     
  7. BusDriver

    BusDriver Veteran Member

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    I agree that sprayfoam is the best you can do right now. There are DIY kits now, and it qualifies you for a tax credit too.

    Do a google search for DIY Spray foam insulation and there's lots of em

    One thing to think of is maybe a foam kit to seal the air gaps with a solid layer, then fill the rest of the space with regular stuff. The air seal will be worth it IMO.
     
  8. Earlsfat

    Earlsfat Veteran Member Lifetime Gold Member

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    Urethane spray foam is HIGHLY flammable and after seeing a sculpted and painted mountain set ablaze by an HO gauge train..... I'd strongly recommend against insulating your home with it. In the event of a fire in the garage (probably the most common place they start) if anyone is in those rooms they'd have almost no chance.

    That's just my opinion.

    I glued rigid 2" blue foam on my garage ceiling, and rented an insulation blower from Lowe's and did the outside walls, floor and ceiling in the one room over our garage... also put down the top of the line carpet pad (the heavy cell foam, not the pressed together crap).... the difference is unbelievable and the whole thing only set me back about $200.00.

    PS: With the blower or the spary foam you have to watch that the insulation doesn't push the drywall off the studs, especially if it's nailed and not screwed.
     
  9. Rick WI

    Rick WI Veteran Member

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    You don't think stro is flammable? Code requires fire barrier anyway, don't recall if 1 or 2 hour rating. It's a mute issue. Besides, nearly everything in a home is flammable and will kill you when it lights.
     
  10. Marks71BB

    Marks71BB Veteran Member Lifetime Gold Member

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    Seal up all the cracks between the joists/floor/walls and stuff it with pink between the joists, then sheetrock the garage with 5/8" drywall.
     

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