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Smart baffles in cathedral ceiling

Ericg_23 | Posted in Green Building Techniques on

Hello everyone, 

I am building a home that has cathedral ceilings and had a few questions. My rafters are 2x12s  and I am going to be installing smart baffles since I will be insulating with open cell spray foam.  I live in Carlsbad,NM we don’t get a lot of rain and is pretty dry most of the year since we live in a desert. Anyways when I had the insulation guy come look at the house he said that I wouldn’t need baffles and not to install them. My only concern is that where I live the day temps can change drastically from the night temps which can be more than a 30 degree change and I fear than condensation could make my roof decking and rafters mold. Any information on this would be great.

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Eric,

    Installers are spray foaming roof cavities with open cell foam in pretty much every climate zone. Sometimes they work, sometimes they don't.
    https://www.greenbuildingadvisor.com/article/open-cell-spray-foam-and-damp-roof-sheathing

  2. k_weston | | #2

    I'm curious to know as well. I'm finishing out a cathedral ceiling space above my garage in SoCal. I was told I didn't need baffles, only insulation. I left a gap between drywall ceiling and fiberglass, and I need to install a trim board at the peak, but there is condensation up there. Last night was 48˚ and low 70's today when I noticed heavy condensation. I can't install baffles now, and I don't think it would help anyhow. But the temperature fluctuation is definitely at play. Looking at a more robust ridge vent like the Cobra Ridge Vent or similar.

    1. k_weston | | #4

      I'm going to seal the ridge cap in drywall and mud/caulk seams before I attach the faux ride beam facing. This will cover those exposed surfaces. Since me eaves are not vented/open, the air is coming from inside the room, not the rafter space. Sounds like your eaves might be vented?

    2. Expert Member
      MALCOLM TAYLOR | | #5

      K_weston,

      You can use permeable insulation (batts, cellulose) in climate zones 1, 2 and 3 without baffles or ventilation, but you need a vapor-diffusion port at the ridge - and a good interior air-barrier.
      https://www.greenbuildingadvisor.com/article/vapor-diffusion-ports

  3. begreener | | #3

    Why not us a nailbase for a thermal bridge (ACFoam® Nail Base) then have him spray some closed cell first then open?

    This way the "first condensing surface" will never reach the dew point & thus no vapor to liquid ...

    That's what I did on my cathedral ceilings in NH

    ~ former spray foam contractor

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