Re-roofing my house, need more attic ventilation??


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Old 06-26-10, 11:17 AM
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Re-roofing my house, need more attic ventilation??

I am in the middle of a grueling re-roof on my house, with extensive wear and water damage. The attic is very, very hot, and from what I have been reading, attic heat is a major contributor to roof wear. Attic heat, 130+, cooks the roofing material from the bottom, and the sun from the top. I have a ridge vent on the longest of the ridges, and vented al soffett all the way around. I thought a powered attic ventilator was the easy answer, but from reading they have a number of problems too: the motors die after just a few years, the elec costs are almost as high as what you would save on AC, can suck the AC out of your house,.... Turbines: The turbines may leak, and hurricanes can rip them off the roof,.... What's the answer? How can I get the attic way cooler? Do I need low Gable vents to introduce more cool air? But they might suck in rain??
Help!
 
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Old 06-26-10, 04:18 PM
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Make sure your soffitt vents are clear and no insulation is blocking airflow to the attic. Can you see daylight when you look at the soffitt area from inside the attic? You should be able to.
Never add gable vents to ridge vented attics, it interrupts the draw of the ridge vents.
I would put ridge vent on all the ridges, full length of the ridges. Get the low profile type that you cap over with shingles to match the roof.
Are there any old roofs in the attic say where an addition was put on and the roof was changed? If so can air flow from one area to the other in the attic?
 
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Old 06-26-10, 04:25 PM
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First, estimate the ventilation area of your current vents. A 12"x12" gable vent may only yield 60% of that area in effective venting. Do some searching to see if you can come up with a derating factor for what you have and a rating for your ridge vent.

Once you have those numbers, if your ceiling is well sealed, plumbing, electrical, and top plates all sealed with a vapor barrier, then you need one sq. ft. of vent area for every 300 sq.ft. of attic floor. If you are not sealed up as listed above, double that number, one per every 150. If your current vent area is low, increasing it will go the right direction.

If your new shingles are a light color, it helps. Balck/dark is bad. There is some research on radiant barrier shingles that simply reflect the heat before it becomes part of your home. Not sure if anything is available.

Once your roof gets hot, the attic will follow and that heat has to be vented somehow. Passive vents require heat to work, so the results are never perfect. Power venting helps, but at a price. Removing trees to increase air flow may help, if it doesn't remove shade trees.

If you think about those pictures of buildings down in the Caribbean, what color is dominant, white. Now you know why, they want to reflect that heat.

Do some calculations and see where you are.

Bud
 
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Old 06-27-10, 03:49 PM
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Why does this forum display posts in rev chronological order?? Can I change it? It's the opposite of any other forum I've ever been on.

Back to the question: Yes I have purchased silver/white dimensional shingles. The soffets are blocked with insulation, but has a Styrofoam spacer to open a vent. hole, so i think they're ok. The ridge vent may have been clogged. I already tossed it.

Is it generally agreed that the low profile, shingle on top, type offer the most flow? I was up there today, all day, and the ridge is semi-sealed, except for 1 hole. I'd expect a rush of hot air, but I felt just a small amt coming out of the hole? Maybe the soffets are not offering enough flow???
 
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Old 06-27-10, 03:58 PM
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Yes...in the user control panel....check user options..you will be able to change it.
 
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Old 06-27-10, 07:53 PM
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Use some type of safe smoke so you can see where the air is moving. ie, are the soffits pulling air in and when in the attic, is the ridge vent working its full length. If not, then that work need to be done first.

Bud
 
 

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