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Using Reclaimed Fiberglass Faced Polyiso….another question

rob kohaus | Posted in General Questions on

Based on advice from Dana Dorsett and Martin Holladay we decided a good wall assembly for using my reclaimed roofing iso in zone 5A was as follows
– drywall
– 2×6 with rock wool
– OSB (substituted for ZIP)
– 3.5″ reclaimed iso
– 1″ EPS
– housewrap

I talked this over with my builder and he had a few concerns.

First is the location of the flashing. With part of the cladding being EIFS, he stated that the EIFS installers will flash on top of the iso, then put on the EPS and then apply the EIFS to that. So he suggested we locate the housewrap between the polyiso and the EPS. Thoughts on this?

Second, he is concerned about not having a WRB actually in contact with the OSB. His worry is bulk water intrusion through all the penetrations (nails/screws) it will take to get the two layers of foam, housewrap and masonry anchored to the wood. He is suggesting a dimpled housewrap between the OSB and iso. Any justification for this concern?


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  1. Expert Member
    Dana Dorsett | | #1

    Lapping the house wrap to the flashing is key. Using the crinkle-type housewrap would be important if between two foam layers, especially when one of then is mildly hygroscopic (the polyiso.)

    Don't sweat the intrusions at the fasteners.

    There is nothing gained by having WRB in direct contact with the OSB, as long as you have a WRB between the foam layers. In fact the tannins in wood products has been a real problem for the longevity of some WRB products, causing them to fail in under 2 decades. (Contact with cedar siding is the most common tannin related failure, but not the only.) That has supposedly all be addressed in he noo-improoved versions, but we don't exactly have a century of data on that.

  2. GBA Editor
    Martin Holladay | | #2

    The requirements of the EIFS contractors trumps everything else. You can't get an EIFS warranty from the EIFS contractor unless the EIFS is installed as required by the manufacturer of the synthetic stucco. That means that the EIFS contractor will include provision for drainage.

    Because modern EIFS systems are water-managed and include provision for drainage, you don't have to worry about water reaching your OSB.

    Of course, if you don't trust the EIFS system -- don't specify EIFS.

  3. rob kohaus | | #3

    Martin - I trust the EIFS system. The concern is more where the siding transitions from stacked stone to EIFS. (the home has stacked limestone about 2/3 of the way up the wall and then a ledge and then transitions to EIFS for the remaining 1/3). To the best of my knowledge, the EIFS installers flash by lapping with the house wrap, then install the 1" EPS over this, then install the EIFS over this.

    Originally we were going to forgo the additional 1" EPS but the EIFS installer insisted. So then I suggested to my builder that perhaps the details would all be easier if everything was in the same plane. Then it became a question of where the WRB should be.

    I thought it would be easiest if the flashing was all to the outside of the polyiso. My builder (and mason) are both accustomed to the WRB being against the wood sheathing (and therefore also the flashing details). So what they want to do is this....
    - studs
    - OSB
    - crinkle type housewrap
    - 3.5" polyiso
    - 1" EPS
    - EIFS or limestone

    They then want to flash everything back to the house wrap.

    I contended that this was unnecessary and proposed the following change....
    - OSB
    - 3.5" polyiso
    - crinkle type house wrap
    - 1" EPS
    - EIFS or stone

    The 1" EPS (seams staggered and taped) would serve as an initial WRB for the whole wall assembly. Then the house wrap would serve as a second (belt and suspenders) barrier

    To my mind, this puts all the flashing details in the same plane (all would be flashed with the house wrap). So it wouldn't matter whether there was stone or EIFS or it was transitioning from one to the other....all penetrations would be flashed based on the EIFS....right?

  4. rob kohaus | | #4

    Dana - Thanks for the additional insights. I read the BSC paper on house wrap failures (albeit it is from 2001). It seems to me for my assembly, I can avoid putting the house wrap against the wood. Not only would this avoid any wood-wrap failure issues, but it seems like the most durable and easy to construct location.

    The possible problem I foresee is convincing the mason, carpenter and EIFS installer that I'm right (this is somewhat uncharted territory for them). My builder has stated he would be more comfortable with the proposed assembly if we stuck with the ZIP instead of changing to OSB. I'm having the lumber yard price the difference. If its not HUGE I may just do the ZIP.......

  5. GBA Editor
    Martin Holladay | | #5

    As long as your EIFS contractor is on board with your plan, I see no reason why it won't work. Of course, the success of your wall depends on the conscientiousness of your workers and the attention paid to flashing details.

  6. rob kohaus | | #6

    We're all (myself, construction manager, mason and EIFS contractor) having a meeting later this week to discuss the assembly and the details. We'll see how it goes.

    Your comment regarding the success of my wall assembly is true of any wall assembly. :) I'm doing the general contracting on the house w/ the help of a construction manager. I've quickly learned that unless I'm looking over their shoulder, an unfortunately high number of tradesmen revert to "business as usual" level of standards. :(

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