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Placement and selection of the elusive barrier.

rainyriver99 | Posted in Energy Efficiency and Durability on

Asking for opinions. I’m in zone 7/8. My plan is for a one story earth bermed home set about 3 feet below grade, bermed to varying heights of 3 to 6 feet. Typical treated lumber wall but with 12″ double stud walls with dense pack cellulose and 2 inch xps exterior with taped seams.The exterior would then be wrapped with heavy poly as per the PWF specs. My question is ” Can I continue the poly sheet protecting the foundation up to cover the entire exterior wall as an air, water, vapor barrier. I would have no barrier on the interior wall since the idea is to dry the walls to the inside. Also, would it make sense to continue the exterior poly over the top plate before setting the rafters to continue as an interior ceiling barrier? Feel free to comment please.

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  1. GBA Editor
    Martin Holladay | | #1

    1. You shouldn't try to use cellulose in a below-grade wall.

    2. You shouldn't install a vapor barrier on the exterior side of your insulation.

  2. iLikeDirt | | #2

    It sounds like ICFs or a concrete sandwich panel with insulation in the middle would be a better plan for these walls. Masonry likes to be buried; wood doesn't, no matter how many toxic chemicals you treat it with and how many layers of impermeable plastic you wrap it up in. Build your walls like a walk-out basement (which is basically what you're envisioning) and you should be fine.

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