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Porch attic

user-6963501 | Posted in Building Code Questions on

Climate zone 2A, Salt air environment close to beach

I am building a new home and have a shed roof entry porch attached to the side of a 2 story wall. Construction is metal roof over adhered underlayment on 5/8″ plywood sheathing on roof trusses with tongue & groove wood ceiling finish.

The preference is not to vent the isolated attic area because of salt air exposure to roof connectors. The Florida Building Code requires all attics to be vented and does not make an exception for attics over non conditioned area. A non vented roof would require spray foam to completely encapsulate the attic area which is not doable. Will not venting the porch attic cause problems?

I have spoken with insulation contractors in the area and they state that a porch in that situation is not usually vented or insulated.

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Replies

  1. Expert Member
    Peter Engle | | #1

    The FBC is based on the IRC, and both have requirements for roof venting. You are right - there are no exceptions for attics over unconditioned spaces. Your insulation contractors are also rightthat most porches are not insulated or vented, and most building inspectors won't require it. You could check with your local AHJ to see what they say. Don't install insulation just to keep the AHJ happy - that would be a waste of resources.

    Functionally, a porch roof with T&G wood on the ceiling doesn't need much ventilation, if any. But, ventilation would help things to dry out if there are any roof leaks. Condensation within the attic won't be an issue. If the AHJ requires ventilation, you could try installing vents in the ceiling. One easy way to do this is to leave a gap of an inch or two between adjacent T&G boards to allow airflow from the covered porch area up into the attic. Install insect screening in the vents to keep the bugs and critters out. One vent at the outboard edge and one inboard will allow a fair amount of wind-driven airflow and drying. Your AHJ might allow this in lieu of another penetration in the roof. Tell him that this is more resistant to water infiltration in hurricanes.

    1. user-6963501 | | #4

      Thank you for your reply. The AHJ is requiring venting.

  2. Expert Member
    BILL WICHERS | | #2

    Just a little out of the box thinking, but would having someone setup an airless sprayer and painting the inside of the attic and all the connectors with a marine paint help with corrosion concerns? Just a thought...

    Bill

    1. user-6963501 | | #5

      I like that thought. Thank you.

  3. Jon_R | | #3

    Sounds like a case where close-able vents are needed. But be careful of humidity in closed off areas.

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