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Community and Q&A

Venting Soffits

bill_setag | Posted in Energy Efficiency and Durability on


Conditioned attic-space home in Houston area, with open cell foam in attic. Blocking 2x will be nailed between roof deck and top plate over WRB. Framing will also be open cell foam. I plan to seal the blocking plate with closed cell foam just after roof deck is installed to air seal the attic. What about the Soffit? I do not intend to have vents in the soffits, is this OK? Will moisture accumulate in the soffit area? Good idea, or not? See attached picture. Thanks.

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  1. Expert Member
  2. bill_setag | | #2

    Many thanks Malcolm for the response on soffit. Would sealing with caulk the Soffit area not with foam cause moisture to fall out on the Soffit?

    Our home is being built North of Houston, and as you know, it gets humid here, all the time. The humidity only drops during winter after a cold front, but three days later, the wind shifts and humid air comes off the Gulf of Mexico ... humidity up and down, all year long. Even during summer, humidity is high in morning and then starts dropping as sun rises. I am no residential home builder expert, and my builder is from old school and has almost zero experience - and could care less - about building science, but I am a Mechanical Engineer and determined that a good HVAC and dehumidifier system, with peel and stick Titanium PSU 30 on the roof, with battens and Boral Concrete Tile, might solve the problem of moisture under the Ridge and CDX plywood. I also have asked the HVAC installer to make a return on the Dehumidifier near the highest roof ridge to help take away any stale, high humid air. I intend to keep my conditioned attic at between 45 and 50%. Of course, all this design is only as good as the installation. Your thoughts on the design?

    1. Expert Member
      MALCOLM TAYLOR | | #3


      Sorry - your section doesn't show an attic so I assumed the house had cathedral ceilings.

      I don't see any mechanism that would cause moisture to accumulate in, or drop from the soffits. As Martin wrote in the first link I provided, venting the soffits can actually cause moisture problems there.

      I don't know enough about building in humid climates to know whether it makes sense to use foam at the roof line, or loose fill on the attic floor. GBA sponsored a discussion on the subject that may give you some good feedback on your plans:

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