Q&A – Attic window opening

Recently, the AskARoofer experts responded to a question about keeping an attic properly ventilated.

Helen, a homeowner from Massachussetts, was looking at their attic and trying to figure out how to ensure airflow remains balanced. Here's what they asked our experts:

I have a ridge vent but no soffit vents. I do have two attic windows. Should I leave the windows open at the bottom a couple of inches?

When John Kenney from Cotney Consulting Group, one of our experts, saw Helen's question, he had this to say: 

Helen, with a ridge vent but no soffit vents, the attic ventilation system is incomplete. A ridge vent is intended to work with low intake ventilation so outside air enters near the eaves and exits at the ridge.

Leaving the attic windows open a couple of inches may provide some temporary air intake, but I would not consider that a proper long-term solution. The airflow would be coming from the gable ends rather than uniformly from the lower roof edges, so portions of the attic can still remain poorly ventilated. Open windows can also allow wind-driven rain, insects and debris into the attic.

From the photo, I would first have someone determine whether soffit vents or another form of low-level intake can be added and whether the insulation is blocking the eave area. That is especially important with an older attic like this, where the original framing may not have been designed around a modern soffit-to-ridge ventilation system.

The ridge vent also needs enough intake area to work properly, so the system should be calculated based on the attic floor area and the published net free vent area of the vents.

My recommendation would be to treat the open windows only as a temporary measure, if needed, and have a qualified roofing or attic-ventilation professional evaluate a proper low-intake solution. If soffit vents are not practical because of the construction, there are other intake options that can be considered.

The main point is that the ridge vent needs a dependable source of low intake air. Cracking the attic windows may help temporarily, but it should not be the permanent ventilation strategy.

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