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Is there a problem with too much attic ventilation?

k8RQsvj3yc | Posted in Energy Efficiency and Durability on

As I finalize the soffit & vent design for my new home, I’m coming up with some out of balance numbers.

The attic area is ~4200 sq ft (this include space over garage). Garage will be insulated and drywalled, preped for heat but not heated at first. Using 150:1 I come up with an NFA req of 28 sq ft or 4032 sq in.

Half of the roof has a 8:12 pitch, the other half 6.5:12

Due to the roof configuration, I’m planning on using ventilated ceiling treatment, such as invisivent) on the porch ceilings to add to the middle roof intake (“true soffits are minimal here).

I also want to use vented soffit (again invisivent) on all soffits (and I have some large soffits). This gives me an intake of over 6139 sq inches. If I put ridge vent on 100% of all ridges, I end up with 2736 sq in of exhaust.

I know intake must always exceed exhaust to avoid negative pressure possibilities, but is this plan too far out of balance to the intake side?

I know the question will come up, why am I using so much vented soffit. To be truthful, just for simplicity of installation and consistency of appearance. Nothing more!

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  1. GBA Editor
    Martin Holladay | | #1

    Don't worry -- your plan is OK.

    Your soffit ventilation area doesn't matter much compared to a much more important issue: air sealing your ceiling. Do a good job with your air sealing details, and the attic ventilation becomes more or less irrelevant.

  2. k8RQsvj3yc | | #2

    Thanks - we plan on a sealing coat of spray foam, no HVAC ducting and very minimal penetrations

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