cold addition floor

cbg640September 28, 2009

I had a 16 x 22 room and a garage added to the house a few years ago. The room is between the original house and insulated garage. The addition floor is cold, the insulation is R30 faced. There is a ventilated crawl space under the room. There is a vapor barrier over the ground. Should I close off the bottom of the floor joists with plastic, wood or insulated foam?

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Normally the crawl space vents are closed in the winter in a cold climate. But I don't know where you live.

    Bookmark   September 29, 2009 at 10:56AM
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Normally, crawl space vents are open in winter closed in summer.

The reason is to prevent warm-humid air from entering the crawls apce in summer where it will condense on cooler surfaces.

But the issue is not probably not with the thickness of insulation in your floor, but more likley air infiltration into the room from holes in the framing.

Adding a layer of rigid foam to the bottom of the floor joists can help...if it can be easily done.

Otherwise you need to find and seal all penetrations and openings from wires, pipes, ducts and other items that may penetrate the floor to the crawl space and which allows air to enter.

Speaking of ducts, what kind of heat do you have?

Do you have ducts run through the crawl space?

To what level are these insulated.

Should be 2" ductboard or insulated to at least an R-8 or more in most regions.

Another option is to insulate the walls of the crawlspace and 'condition' the crawlspace, either by heating it, cooling it, dehumidifying it...or all 3.

    Bookmark   October 3, 2009 at 7:03PM
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There is only insulation under the floor. The new room sits lower than the existing house. I was able to tap into the hot water line and bring the return line over the fins. I had another person tell me to box it in with 1/4 plywood to keep out the drafts. I checked last winter with both exterior vents(front & back) closed and the window to the original basement(side) opened. I could feel air flowing. I left it open a while to let the temperatures equal, but a day later there was still air flow.

    Bookmark   October 6, 2009 at 6:31PM
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