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Destinmatt said:
I thought you had to get good ventilation in the attic to prevent mold.
That gets over exaggerated as much as the need for grounding your dust collection and that PVC air lines will blow up and kill you.
Mark
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My last house was built in 1975, and had a small (shallow slope roof) unvented attic. Worse, the upstairs bath fans blew right into the attic, not through the roof (I fixed that part in 1990). Anyway, there was no sign of any damage to any fof the roof decking, no mold/rot anywhere, and no shingle damage. I asked here if it was ever OK to have an unvented attic, and pretty much was told it was absolutely not OK. Still, that didn't jive with this particular experience. Somone did say "if it ain't broke, why fix it?"...I'm kinda in that camp. If there's no damage, I wouldn't fret too much. If you want to vent it, go ahead...it's your house and the venting may help with the summer heat.
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The attic venting isn't to keep mold out of the attic, it's to keep the underside of the roof cooler to extend the life of the shingles. There shouldn't be anything in the attic producing mold. Bath exhausts, etc should be vented to the outside.
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The reason mold grows is because there is moisture. No moisture, no mold.
The reason attic spaces are normally vented is because of ambient moisture and for insulation assistance. Hot attics transfer heat to interior spaces.
There is really little to be gained in adding ventilation to the top of the roof if there are no areas for air to get into the lower sections(soffits/etc.) of the space. The air will have no way to move.
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Doesn't get cold enough for long enough here to get enough moisture to condensate up there. We didn't even have winter this year. Coldest temp was 24 and the next coldest was 25 and they were the only days in the 20s this "winter". The bugs are already bad...
Ventilation here is for heat only moisture isn't a problem as the humidity is generally high most of the year but not cold in the winter to condensate and the attic temps will be upwards of 140* in the summer so the relative humidity goes down anyway.
Lots of soffit vents cut in around the house and some sort of venting on the roof. Ridge vent doesn't flow enough cfm for roofs here by itself. The old whirlybirds are still the most effective here.
The best solution is to have spray foam applied to the roof deck. It is the recommended way to insulate a house here though it's pricey. The easier and cheaper way is to put a layer of 4" foam down before the roof decking.
So basically you insulate the roof instead of the ceiling and the attic is now a tempered area that also keeps heat out of your ac ducts.
Take a look at the building science web site as they have good pics and descriptions of how it should be done.