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We just finished all of our inspections on a house built in 1973 that we plan on buying. the house is in North Texas and upon inspection into the attic space, it had no ventilation, very little insulation, and surprising to me no mold. I thought you had to get good ventilation in the attic to prevent mold. How does this unvented system work and do I need to look into converting to a vented system and/or add insulation to the attic floor or roof sheathing? When I search unvented attic, I get hits on spray foam and rigid foam that seem fairly modern in concept.
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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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I've often wondered how crucial some things were too. The roof joins almost directly with the wall on the back of my house, no overhang for a soffit vent (1976 house). And I've seen houses on TV where they spray foam the underside of the roof. Definitely no room for venting there. But maybe if it's actually sealed well enough it prevents certain problems?
Benny
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Since I live in the area in a similar house I would defiantly recommend venting it. I put 10 soffit vents around the perimeter and a couple of the round spinners up high on the roof line. It probably has dropped my attic temp at least 20 degrees during these Very hot north Texas summers.
It's easy to do and really pays off on your ac bills here. The mold thing is just a nice side benefit.
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bennybmn said:
I've often wondered how crucial some things were too. The roof joins almost directly with the wall on the back of my house, no overhang for a soffit vent (1976 house). And I've seen houses on TV where they spray foam the underside of the roof. Definitely no room for venting there. But maybe if it's actually sealed well enough it prevents certain problems?
Every 5 years or so I get ice jams on my gutters and I think ice forms inside the eaves too.
This is an image of ice jams (not from my house, but typical):
http://www.sparklewashmn.com/uploads/ima...to%201.jpgI think better venting would prevent this from happening.
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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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K. L, McReynolds said:
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.
My house has a series of 1" diameter soffit vents. I will be replacing the soffits this spring and I will be putting in much larger vents. I will not be putting them in front of windows however as I run an whole house attic fan and I don't want to suck super-heated attic air into the house.
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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.
