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We are in southeast Idaho, have a plain simple gable roof on a 1,050 square foot floor house; the roof's pitch is not great, probably 3 or 4/12 but normal for our area.

We have 1 vent at each gable end (so 2 total), rectangular and about 12" by 24" in area. We have five vents spaced evenly along the roof, about a foot down from the actual peak. Inside the attic I see the vent holes are about 12" in diameter.

I keep reading that my square inches are probably good for air flow, but I'm wondering if I still need to put in some soffit vents and baffles for good circulation. The people before me vented the bathroom fan right into the attic so I want to avoid installing a new roof again (it was replaced last year-shingles and all plywood panels).

Given this, yay or nay on needing soffit vents and baffles?

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2 Answers

up vote 3 down vote accepted

In a nutshell, yes, soffit vents prevent moisture from doing bad things to your home. Greebo is spot on, you want soffit vents for your air intake.

Without a continuous flow of outside air, the attic heat in the winter will melt ice and snow at the top of the roof, which will flow down and refreeze when it reaches the cooler bottom of the roof. This forms an ice dam, backing water up into your shingles and roof, resulting in some potentially expensive damage.

You also want to draw air in from the soffits which are on the underside of the roof and exhaust it at the top, which requires at least the same, if not more soffit vent area than you have ridge/gable vents. This prevents wind blown moisture from being driven up into a ridge vent and into your attic. If there is a positive flow of air out the ridge vent from the soffits, this minimizes the risk of the ridge vent becoming an intake vent.

And finally any moisture that does accumulate in your attic will be quickly vented away by the airflow from the soffit to the ridge vents. This includes any moisture from the outside reaching the dew point and from any moisture from your home that escapes into your attic from any cracks.

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Both great answers and close to each other, I'll mark this one because of more detailed answer with a couple more considerations (so now I know a bit more). Thanks to both! –  Kirk Hings Oct 12 '11 at 3:46
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Assuming you've fixed the "lets dump all the shower moisture into the attic and rot the roof" problem...

Yes, I think you probably should add soffit vents with baffles. I say this because from your description, all of your air circulation is at the top of the attic. Air flow through an attic with no fan is done purely via convection. In order for air to get into a space, air must be able to get out of a space. If you have gable vents and your peak vents all at the top of the roof then the only place air can really flow is up top.

Adding soffits will allow for cooler, outside air to be drawn in from the bottom of the roof line, where it will displace the hot moist air trying to get out, creating much more efficient air flow overall.

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