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Proper ridge and soffit venting with a whole-house fan

I just installed a Cobra Snow Country Advanced continuous ridge vent. It provides two sqft of net free area. I understand that this should be balanced with an equivalent amount of soffit vents (yet to be installed) for a combined total of 4 sqft nfa. I have gable vents that I will be closing off so that I get the proper airflow from soffit to ridge. Simple enough. Now the complication: I have a whole house fan that requires 7 sqft of nfa.

So here is my question: What is the proper way to increase the nfa from 4 to 7 sqft but still achieve the proper passive airflow from soffit to ridge when the whole house fan is not in use?

I could increase the soffit venting to 5 sqft but wonder if this would upset the soffit/ridge interaction.

Or I could add 1.5 sqft of standard box vents near the ridge and increase my soffit venting the same amount for a total of 7 sqft of nfa.

Thanks for any suggestions.

By the way, i am in zone 5.

Asked by Steve Hamson
Posted Thu, 01/02/2014 - 17:57
Edited Fri, 01/03/2014 - 06:57

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Steve,
Q. "What is the proper way to increase the net free area from 4 to 7 square feet but still achieve the proper passive airflow from soffit to ridge when the whole house fan is not in use?"

A. Install gable vents.

To learn why adding gable vents won't cause problems -- assuming that you have achieved the most important goal, which is to build an airtight ceiling -- see All About Attic Venting.

That article quotes venting expert Bill Rose, who wrote, “Once you’ve sealed all of the openings that lead from below into the attic, corrected the ductwork, and installed a nice thick blanket of insulation in the attic, then one venting strategy is about as good as any other. Gable venting and ridge venting are both fine. Soffit venting with baffles is fine. Combinations are fine. If parts of the roof have a lot of venting and other parts have little or none, most would agree that that’s fine too."

Answered by Martin Holladay, GBA Advisor
Posted Fri, 01/03/2014 - 07:10

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