Ernie Gladstone
5/11/2007
I installed a metal roof on 2x4 strapping (with tar paper between) 10 years ago. The strapping is nailed directly to roof rafters (no plywood between). This past winter, i noticed water (frozen) on the insulation between the rafters. I believe it is a result of the metal roof condensating on the north side and water is somehow making through the tar paper which has sagged between the strapping. I am considering lifting the roofing, laying plywood over the strapping, and then replacing the tar paper before putting the roof back down to rectify this problem. I am curious to know if anyone else has experienced this problem (condensation) or has simpler (and cheaper)suggestions on how to fix my problem.
Todd Miller
Classic Products, Inc.
5/11/2007
Ernie, you may have several options here. One option might be to increase attic ventilation. That could resolve things. Your idea is also an option. Talk to an experience insulation contractor but spraying icynene insulation on the attic ceiling may also be an option. Hope this helps.
Bill Smith
7/10/2007
I have 2x4 strapping or purlins nailed directly to my rafters, and my metal roofing is nailed directly to the purlins. So when you go in my attic, you can look up and see the underside of the metal roofing. I live in a humid area (south Georgia), and sometimes when the roof is cool, the moisture in the air condenses on the underside of the roof and drips in the attic. I don't have the ice problem, though, because of the warmer climate.
Todd Miller
Classic Products, Inc.
7/11/2007
I would suggest increasing attic floor insulation as well as attic ventilation.
Guest User
8/15/2007
I'm pretty sure you have a heat loss due to air exfiltration problem that is causing condensation to occur on the cold side. Warm air seeks its way out of the building at the top. Do you have tongue and groove wood as an interior finish? Tongue and groove wood lets a ton of warm air past it that then easily gets by your fiberglass and condenses were it meets the surface at the dew point - in this case the cold side of your rinsulation. A building in a cold climate needs a continuous air barrier to keep this from happening. Sheetrock is typically this air barrier but if you don't have sheetrock then you need something else like rigid board insulation, plywood or spay applied closed cell foam. But keep in mind, this air barrier must be on the warm (in winter) side of the insulation. If you put the plywood where you suggest my thinking is that you will condense on the plywood and the plywood will grow things and rot. If you have sheetrock or think you have a tight interior ceiling then hire a pro and have an energy audit done including an air leakage test and/or an IR scan done and you will see the leaks. Solutions are difficult ... but it requires sealing the interior surface. If you have recessed light cans - lose them - if you have tongue and groove (short of removal)you can try sealing the grooves with a clear caulk and the edges. Good Luck!
Todd Miller
Classic Products, Inc.
8/16/2007
Good advice.
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