Attic Ventilation - NFVA Calculation

I’ve inspected a new home with an attached garage. The attic area for the garage is open to the area over the living space. There is no top vent on the garage gable, but one lower vent. I reported lack of top vent on this gable.

The builder responded saying that the NFVA calculation only applies to conditioned spaces, however; one of the lower vents used in their calculation is actually located in the unconditioned space of the garage. “Per code attic space that is over conditioned space is what we look for when running our calculations. What you will see when you open the file is that this roof requires a few things to be code compliant”

The issue is that the unconditioned garage space adds a considerable amount of area and would change the calculation from approximately 50% in and 50% out to having insufficient output capability.

Is the builder correct that the building code ignores the area over unconditioned spaces even though the attics are connected and essentially one space? Is the calculation affected because one of the lower vents is in the unconditioned area?

It’s been my experience with several warranty inspections for new homes with a similar configuration that cracks form in the garage ceiling or the owners complain about how hot the garage gets.

Pictures show the garage gable with no top vent, one bottom vent used in the calculation in the garage area.and the builder’s engineering calculation

![SnipImage (002)|367x500](upload://pxXWwR5jgSwXAr0qpQoRIfyVGsG.jpeg

You’re straying deep into the weeds on this. Call out the apparent insufficiency of attic ventilation, and recommend 1) getting written confirmation from the builder that the venting meets current code, and 2) an assessment by an indoor air quality professional.


The code does not mention over “conditioned spaces”. It appears the attic is designed to rely on a power fan to vent. Do you know how many CFM the fan is? and the attic’s floor space sqft?

The entire space figures into the NFVA calculation, including the eaves, porch covers, garages etc. that communicate with the main attic. Even houses with unvented attic assemblies require ventilation for the isolated attic space over the unconditioned garage.

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Get a professional assesment so that you won’t have trouble later, better this way. I’m looking into attic ventilation too cause I had mold last year and I don’t want it to repeat again. Have any of you tried solar fans? Found some here can’t say anything necessarily impressed me, but I’ve been looking for a while and I’m pretty much leaning to just get one that covers the size of my attic and get it done with if I don’t get any clear suggestions in regards to a specific model, or at least a brand that’s worthwhile.

Where are you located?

Morning, John. Hope this post finds you well.
Besides what Chuck correctly stated, take roof deck sheathing into considering when visually ascertaining attic circulation.