What attic ventilation strategy is appropriate for my house?

Question

We're trying to assess our attic ventilation and would love any feedback or advice.

Our attic is 1600 sqft, our roof slope is 2.28:12, and the prevailing winds in our area are southwest. We have attached an image below showing the location of all vents. We presently have:

• 13" x 5" soffit vents x 17
• 37" x 18.5" front gable vents x 2
• 24" x 12" rear gable vents x 2

Combined, this is 21.2 sqft of ventilation, but the vents all have wire mesh with an unknown open area %. It's probably greater than 50%, which gives us at least 10.6 sqft of ventilation.

Our roofer wants to install three 11" diameter circular low profile vents on the roof, but we think this is marginal at best, and counterproductive at worst, as it could conflict with the circulation pattern of the gables. If more ventilation is needed, we would rather use a non roof-penetrating solution such as gable vent fans (or whatever you might suggest!).

Our main questions are:

1. Is this enough ventilation for the space? The 1/150 rule suggests that we need 10.7 sqft, which we satisfy even if the screens block 50% of the vent area.
2. Does this create an adequate airflow pattern throughout the attic?
3. If there is not enough ventilation, are there non-roof-penetrating solutions you would suggest?

Thank you in advance!

Answer 1

Consider adding the roof ventilation as suggested by the roofer. Heat rises. This will enhance the ventilation supplied by the gable ends by not depending on air pressure to move the heated air out of the space.

A better solution than the low profile vents is using Chimney vents that use the chimney effect to enhance ventilation, are non-directional and require no electricity. You will need two.