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Hardie Board Prevail panels over exterior EPS board

Mike Taylor | Posted in Green Building Techniques on

I Live in dry and cold Alberta, Canada. I am planning to install Hardie Board Prevail boards  attached to 1×4 strapping over 4″ of EPS insulation . I will be using a Tyvec barrier on the sheathing below the EPS. The Hardie installation guide calls for a water-resist barrier on top of (on the outside of) the foam as well.  Why? Is this necessary? Surely it will serve to trap water vapour within the foam rather than release it? I would like to hear your thoughts on this. Thank You.

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Mike,

    There is no reason to use two WRBs. Where you put it, over or under the foam depends on how you want to integrate it with openings, etc. Both places work fine.
    https://www.greenbuildingadvisor.com/article/where-does-the-housewrap-go

  2. Jon R | | #2

    And even if you did use two, WRB is quite vapor permeable and so it wouldn't trap water vapor.

  3. Mike Taylor | | #3

    Thanks, Malcolm and John. I've read 'where-does-the-housewrap-go' and my windows will be 'outies' so I'll put the WRB on the outside of the 3" EPS foam board. Any recommendations for WRB?

    1. Expert Member
      Malcolm Taylor | | #4

      Mike,

      I like Tyvek Commercial. It's a lot like regular Tyvek, but much harder to tear.

  4. Mike Taylor | | #5

    Thanks. I would think that putting WRB on top of EPS foam is not easy and because it is only sandwiched every vertical 16", easier to damage before the Hardie Board panels are applied; so, I appreciate the Tyvek Commercial advice. A peel and stick product may make application easier. Is there such a product that adhers to EPS foam board?

    1. Expert Member
      Malcolm Taylor | | #6

      Mike,

      I've never used an adhered WRB. Looking at some of the manufacturer's installation video, two guys seem to have bit of trouble putting it on a mocked up wall in a shop. Maybe it's easier, or maybe it sticks to itself at every opportunity and is a nightmare.

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