leav air gap between floors?


Old 12-11-13, 07:45 PM
Thread Starter
Join Date: Nov 2007
Posts: 5
leav air gap between floors?

Hi, we bought a 1977 tri level in Knoxville TN recently. My daughters rooms are over the garage and they get pretty cold at night. I tore out a piece of the drywall in the garage ceiling and saw that 1. there was no insulation and 2. There are trusses between the floors, not joists (I assume for pipes, HVAC or whatever). I want to install some insulation between the garage and the bedrooms to help with the cold, but there is about 18" between floors and that would be overkill if I filled it with insulation. So my question is, should I leave an air gap between the upper floors and the insulation, or put the insulation against the upper floors and leave the gap between the insulation and garage ceiling? Also, R-value recommendation for this application?

I know there are HVAC leaking issues with the bedrooms as well, which is contributing to the cold, so is insulating between floors overkill once the HVAC issues are fixed anyway, or is it a good idea?

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Old 12-12-13, 05:31 AM
Join Date: Oct 2008
Location: New England
Posts: 9,995
Insulation is definitely needed as living space over a cold garage is one of the most mentioned cold spots in a home. And one of the most difficult to insulate.

The two options you mention have pluses and minuses for each. Considering the web trusses and those ducts, my approach would be to insulate below and leave a space above. The trade off is you will lose a bit more heat, but have warmer floors. Since you have plenty of space, going with some extra insulation will make up for the loss of r-value and warm floors are a welcome side effect.

You will still want to air seal those ducts, that warm air carries a lot of moisture into this cold space. But, if you can get all of your new insulation below any ducts, any heat they lose will go towards warming the floors.

As for how much insulation and how to insulate those web trusses, that's more difficult. Were you planning on removing all of the drywall? Web trusses are often spaced differently, not making it easy to install the more common batt insulation dimensions. Can you take a picture of what you are seeing through the inspection opening?

OR can have different climates, but I'm thinking r-38 as a minimum. The trick will be getting it detailed enough for a quality installation with no air leakage from below. Being a garage, fire rated drywall and air sealing are a must. Check local codes as well.

Old 12-12-13, 01:00 PM
Join Date: Mar 2013
Location: USA
Posts: 33
Good Advice Bud.

Try to thermally uncouple the spaces and framing.
Old 12-14-13, 07:29 AM
Thread Starter
Join Date: Nov 2007
Posts: 5
Thanks for the advice. It is about project #3 on my list, so I'm not ready to tear out the drywall yet. But I'll post pictures as soon as I get the drywall down. Hopefully, sometime in January.

Thanks for the replies.

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