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Community and Q&A

Insulating exterior soffit

wzrdmatt | Posted in General Questions on

Hello, as part of our new home we have a filled encapsulated attic space, filled with spray foam.

The local inspector said that we must also insulate the soffits on the exterior of the house, as they have no ventilation and will be fully enclosed spaces. Basically spray some foam into each soffit overhang to fully insulate them.

The soffits are fully blocked off from the house.

Anyone know if this is right, wrong or indifferent? Is there any inherent benefit to doing this, or risk?

Thanks for your help. If you know of any code that requires this, I’d like to read up and educate myself.

Ps. We’re in California, in a designated unban interface zone (ie higher fire risk zone, if that makes any difference.

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  1. Expert Member
    Michael Maines | | #1

    IRC R806.1 does imply that space needs to be filled or vented:, but it's not something I've ever seen enforced in the field, but it sounds like you have a stickler for an inspector. You could add a few button vents to the bottom of the soffit; a total of 1/150 of the soffitted area would meet code requirements.

    1. wzrdmatt | | #2

      I forgot to reply, but Thank you Michael for the input! Much appreciated.

  2. user-5946022 | | #3

    Also, looking at your detail, it appears the spray foam insulation is ONLY between the rafters. It is my understanding that at the perimeter you want this to extend down on top of the top plate and as far into the attic as need to create BOTH an air seal AND the appropriate R value of insulation. Otherwise you effectively have 0 R value at that point where the rafter sits over the 2x top plate.

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