Attic Insulation Controversy


Old 12-09-07, 06:24 PM
Gen is offline
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Join Date: Jun 2006
Location: US
Posts: 374
Attic Insulation Controversy

In my attic I have the ability to close off these huge traingular vents on each end of the house. They have a base about 8 ft long and aprox 3 ft high from the base to the peak.
I keep these open in the summer, but thought maybe to close them in the winter to keep the upper floor warmer.

Then I heard "some expert" say that the attic should stay aprox the same temp as outside, otherwise moisture drastically reduces the insulation's effectiveness. (Potentially making the house colder)
What do you guys think??
Should I close the attic vents in the winter? (My insulation is old and crappy anyway)
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Old 12-09-07, 07:17 PM
Join Date: Sep 2005
Location: ohio
Posts: 195
He was right but not quite for just the reason he gave IMHO. Yes increased moisture or wet FG that stays wet will see a reduction in R value..that is true. But you need to keep your attic cold in winter and have good ventilation cause if that warm moist air that is unfortunately leaking from down below is allowed to build up bad things happen: Attic temp rises above freezing and warm moist air condenses on your actual roof sheathing, nails etc any cold surface and promotes rot. If you live in a snow climate you can get really bad ice dams which again can really mess up your roof and even rooms below.
Its best to have correct ventilation in all seasons most especially if the ceiling is leaky. Better yet to seal and insulate it and ventilate it correctly then you will waste less of your money
Just one more thing, It doesnt apply to your situation but some people have "hot roofs" with no ventilation at all but it takes alot of careful work (usually professional) to seal it all and isnt a weekend diy thing i think..
Old 12-09-07, 07:30 PM
Join Date: Nov 2001
Location: USA
Posts: 1,873
Leave the vents open.

Vapor barriers do not stop moisture flow, they slow it down. As well as insulation does not stop heat flow, it slows it down. In other words there is a constant flow of heat and moisture into your attic. The amount is determined by how well your vapor barrier and insulation performs.

The sole purpose of attic ventilation in cold climates is to bypass the "Low Vapor Permeability" of roofing materials. In other words roofing materials by design deter moisture penetration. Though it does so to keep rain and snow entering the attic, it will also prohibit moisture inside the attic from escaping the attic.

If you need proof of this, close the vents and tomorrow morning go into the attic and you will find moisture on the nails on your roof decking. If it is really cold in your attic, that moisture will be in the form of frost.

Then open your vents and do the same the next day and you will not find any moisture on those same nails.

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