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Home Guy Home Guy is offline
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Default Ridge Vent or Box Vents?

" wrote:

I try to not have my attic temperature exceed 100 degrees F.


100F isn't much in temperature for an attic.


During the hottest 6 weeks of the summer, my attic can reach 100f by
10am. And even with the fan turned on at 10am, the attic will still
climb to 120f by maybe 2 or 3 pm.

My concerns about high attic temperature are evenly split between the
heat-load to the house air conditioner and the impact of the high
temperature to the life of the shingles.

So a few dollars a year of electricity running a couple 1/8 hp motors is
insignificant compared to the perceived benefit in the reduction of
attic temperature during the 2 or 3 months that the fan is used.

Take a look at the post by HeyBub where he goes through the
calcualtion. His target of 1 sqft of vent for every 150 sqft
of attic I've seen used before and seems reasonable.


I feel that the existing formulas are ad-hoc and don't really see any
need for them, especially for new construction (where the eves don't or
won't or shouldn't be sealed on the underside with solid press-board or
plywood anyways).

If you want an even air flow under the roof deck from bottom to top (and
you should want that), the only way you're going to achieve that is by
having either a completely open soffit (open on the underside - no
plywood) and then cover the underside with 100% perforated aluminum - or
put a vent hole every 16" along the entire length of the eaves if you
have a solid wood underside.