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Community and Q&A

Protecting bottom edge of exterior foam insulation board

Salesi | Posted in General Questions on

Which would be better to protect the bottom edge of 1-1/2″ exterior foam insulation board: using a piece of 1-1/2″ x 1-1/2″ treated wood around the perimeter of the house between the foundation and sheathing or using a piece of aluminum flashing bent in an L shape like a big drip cap? The foam insulation board would sit on top of either the treated wood or the L shaped flashing protecting it from insects and mice as wells as keeping it dry. Thanks.

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Replies

  1. Charlie Sullivan | | #1

    How and where is the foundation insulated?

  2. Expert Member
    Armando Cobo | | #2

    I would leave 3/8” min. space between the foam and the drip cap, or flashing, or wood for proper drainage, if needed, either bottom edge would work. I would also wrap metal screen behind the foam and in front of the foam and/or rainscreen, to avoid bugs, termites, and mice.

  3. Expert Member
    Zephyr7 | | #3

    You can get perforated metal strips ready made for this purpose. I prefer stainless steel here since certain soil conditions can corrode aluminum over time. I would try to avoid solid metal flashing here for fear of it collecting water. Perforated metal won’t collect water.

    Bill

  4. Expert Member
    Malcolm Taylor | | #4

    Salesi,

    if your WRB is on the outside of the foam there is no harm in using a PT block underneath it. You still need a perforated flashing, or something like Cor--a-Vent, to seal the bottom of your rain-screen cavity though.

    Or you can do as Bill suggests and deal with both things at once with one piece of J-shaped perforated stock.

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