Attic ventilation question

My 3000 sqft, single story, house has screened soffit openings (8"x16") into the attic, every 15 feet.
However, there is no vent in the roof, at all. The roof is cement tile over plywood and tarpaper.
I suppose, the design relies on cross ventilation between soffits.
Is this acceptable or should I install additional vents in the roof? (not easy!)
--
Walter
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into
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I will bet there are gable vents on the ends. Up near the roof.
Personally I would not try putting new holes in a tile roof.
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I don't do this for a living, but my homeowner discussion with roofing and inspector types indicates that you really would want to add a gable vent to this mix, and/or some active device (powered ventilator) to improve the airflow situation there. Though, all these discussions have been in the context of asphalt shingle roofs.
Another important thing to verify is that your bath exhaust fans really do vent out to the roof vs into the attic, for the obvious moisture reasons.
Best Regards, -- Todd H. http://www.toddh.net /
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Pop makes a point. Get into the attic and check, if you haven't already.
I suggest you look at the Building Science Corporation web site. It has some useful research on venting.
TB
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Are you sure you don't have a ridge vent? Sometimes they aren't continuous, and sometimes are hard to identify unless you look closely.
If no ridge vent, yeah, you need to do some research and add some venting; there are several alternatives.
HTH, Pop
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Walter R. wrote:

I would guess every 15 foot is too little. However since we don't know how many 8x16 vents you have it is not possible to suggest if that is enough or not. In any case it looks like you have a lot of inlet, and not outlet. Which means you have very little effective venting.

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Joseph Meehan

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Walter R. wrote:

No, half of the opening area needs to be low (the soffits) and half has to be high (gable ends, or roof openings). The system may rely on openings in the roof that lets air flow out under the tiles.
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In alt.home.repair on Sun, 31 Jul 2005 17:07:07 GMT "Walter R."

I doubt it. If you don't have a thermometer that goes over 1x0 degrees, how early does it reachthat temperature? How hot is it outside? Maybe you could use an oven thermometer to measure the temp in the attic, not kidding.
My guess is that it shouldn't be over 125 when it is 95 outside, with a fan at least. Less if possible.
Do you have gables? Some houses just have roof on four sides, with mini ridges between the end roofs and long roof parts.

How big are these tiles? Maybe a few could be removed, and then trimmed and replaced to make a 14?" round hole.
If you end up putting in a fan, you should know that I get a cover of "lint", mostly natural air-born plant stuff I think, over my soffitt screens, every ten years or so, and mine are 6 inches wide but continuous, except for where the joists are. You have much less soffit venting now, so your lint will accumulate faster in inverse proportion to mine.
Meirman -- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.
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