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Is it okay for an attic in a hot-humid climate zone to have no ventilation of any kind?

bobhoperises | Posted in General Questions on

^title. I understand why adding ventilation won’t produce good results, but is it really okay to have no ventilation in the attic at all?

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  1. Expert Member
    Akos | | #1

    Yes if you have vapor impermeable insulation. This could be spray foam under the roof deck or rigid foam the outside of it. You also need to supply conditioned air to the attic.

    You can go semi-unvented with fluffy insulation but you need to provide a vapor diffusion port at the ridge. This works in warm climate zones only (1-3):

  2. walta100 | | #2

    Seem to me there are 3 types of attics.

    Vented is ease, lowest cost and safest choice.

    Conditioned is the best option if for some reason you refuse to say no to the foolish ideas that you must have your HVAC system in your attic and or you must have spray foam between your rafters.

    The option you have preposed is the Clint Eastwood attic it boils down to do you feel lucky. Yes, it has worked out for some people for some unknow amounts of time but not everyone and not always. I don’t think it is code approved. From time to time the dew point of the air in the attic will exceeds the temp of the walls and roof. When this happens, things get wet the question becomes how wet, how often and will it evaporate before mold and rot take hold.


  3. Expert Member
    KOHTA UENO | | #3

    If you wanted more information on using a diffusion port in Climate Zones 1-2-3 with insulation at the attic floor, check out Figure 2 in this guide:

    GM-2101: Guide For Building Conditioned Unvented Attics And Unconditioned Unvented Attics With Fiberglass And Mineral Wool Insulation

    1. bobhoperises | | #4

      This is exactly what I needed!

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