Ceiling Insulation in Rowhouse


Old 12-03-10, 12:14 PM
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Location: Maryland
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Ceiling Insulation in Rowhouse

I have a rowhouse in Maryland which I'm about to insulate. The ceiling joist are only 2x4's on 16 " centers. There is at least 16"s of space between the roof and the joists. I was going to put R-19 up there. My brother in law (the architect) said that code was R-30 but he mostly does commercial stuff and has been mistaken about residential. I always thought that the insulation thickness was based on the thickness of the joist and that the R value would not increase if the joists were to thin.....so

2x4 joists uses R13
2x6 or 2x8 joists use R19

Any guidance would be helpful.
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Old 12-03-10, 12:39 PM
Join Date: Oct 2008
Location: New England
Posts: 9,999
More is better and covering the joists will give you a better installation. Wood is a poor insulator, so the less that is there the better. I'm not sure what Maryland requires for insulation, but I would suspect R-30 would be a minimum.

If there is any venting up there, soffits, ridge, or gable, be sure your insulation does not block the air flow. The other step is to air seal where ever possible before the new insulation is added. Air leakage is one of the biggest sources of heat loss and can significantly reduce the effectiveness of your insulation efforts.

Check mineral wool batts, they are dense enough to block air flow and a better insulator IMO.

Old 12-05-10, 06:07 PM
Join Date: Oct 2004
Location: PA
Posts: 1,840
I forget where i saw the fancy explanation and diagram but as bud said, cover the joists. It may be called conduction, but the warm air comes up thru the joists themselves so if you block them it's better.
Old 12-05-10, 08:00 PM
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Will do, thanks guys.

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