External insulation and cladding over Nexcem / Durisol / Faswall block wall?
Hi folks,
Building a small home with Nexcem (or equivalent) blocks in the rocky mountain foothills. The 14″ blocks with mineral wool inserts will satisfy local energy codes but I’d like to enhance performance with ~2″ of continuous external insulation (Rockwool) covered with an outboard rain-screen cladding system (with requisite gap). Been working with RDH to fine-tune details.
[Side note: I’ve reviewed the 2D THERM analysis from Nexcem, and feel the performance #’s may be oversimplified. I’ve also read the previous relevant Q&A thread from this website on this topic.]
Back to the primary query, I’m wondering if anyone has built a similar system and can offer some insights on key details, lessons learned (etc.) for the block-external insulation-rain screen approach. One specific question is whether to make the cladding fully water shedding or allow for gaps between panels, as is often done on commercial rain screens. If the latter, I worry about the combination of wind-driven moisture and dust buildup behind the cladding.
Much obliged,
AJ
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Hi AJ,
We are currently designing something similar with Faswall (http://faswall.com/) which I believe is very similar to Nexcem. I am curious what you used as your water resistant membrane behind the rain screen but in front of the Nexcem? We are debating between a standard building wrap product which is cheap and easy or parge coating the entire exterior surface of the Nexcem and then using a liquid applied water resistant coating over that.
I am concerned that with a building wrap if an water gets behind it that water will sit in the voids of the Nexcem.
Thanks,
EK
Hi EK,
Alas, I had to put my project on hold another year, but I was wrestling with the same question. I share your concern about water in the Nexcem voids, although I've had a sample outside for more than a year and the stuff seems pretty inert. BUT, the sample is exposed to the air, which is certainly different from what might happen in a relatively sealed wall cavity. I was leaning towards a parge coat as well, but not cheap. Let me know what you decide and how it works out!
Cheers,
Aj