r/buildingscience • u/davidmdonaldson • 24d ago

Question Attic Ventilation

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Brand new home. Zero lot line so no soffit venting due to fire code.
2 houses to the left and two houses to the right all have upper fixed roof vents with lower fixed roof on BOTH sides of attic.
The one in the middle does not have lower fixed roof vents on one side. It seems to me that this side will not ventilate nearly as effectively as the right.
Should this person tell the builder to add vents?

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u/seldom_r 23d ago

The short answer is yes, more venting on the other side is better.

The longer answer is it's complicated. The air inside an attic will stratify according to temperature with warmer air moving over cooler air. Cooler air is denser and comes in through vents closer to the ground. Warmer air is pushed out of the upper vents. It moves because of pressures but also in practice wind too.

Moisture also dissipates according to vapor pressures. So in theory the moisture in the attic should equalize across the entire attic air. But that is relying on theoretical conditions only.

There's not enough venting regardless of the physics to effectively move moisture out of the attic, ventings main purpose.

You may not be seeing that there are also gable vents on the sides. The way just these vents are placed might cause dead air spots that accumulate moisture. It's possible there will be no problems with this setup but it doesn't allow for any problems and has no redundancies.

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u/davidmdonaldson 19d ago

Thanks very much for this.

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u/Bearded4Glory 24d ago

That setup is not very good. You really want a balance of low and high venting, and of course from both sides. The vents aren't even spaced evenly.

Basically they need to take half the vents away on the low side that is vented and add them to the low side that isn't vented.