Z-girt, insulation board, and metal siding
I’m building a cabin out of Faswall hybrid ICF blocks and plan on adding an additional 3″ of Roxul Comfortboard on the outside wall before installing metal siding. I had planned on using one layer of 1.5″ Roxul then screwing 2×4 furring strips in place with an additional 1.5″ of Roxul in between the furring. But wouldn’t it be more efficient to just use metal z-girt strips with a 3″ web to support both the Roxul and to mount the siding to?
I’ve been digging around trying to find the right product for exterior use in a heavy enough gauge to support the metal siding but am having a hard time finding the right product. Am I missing something here or does it make sense to use the metal z-girt?
Dave W.
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Replies
David,
There are two issues here: the structural issue and the thermal issue.
I have no idea whether steel Z-girt will hold up siding for the next 80 years. I suppose the answer to that question depends in part on the weight of the siding and the fasteners that are recommended by the siding manufacturer, as well as the likelihood that the metal Z-girt will rust. At a minimum, you'll need to contact the siding manufacturer. It wouldn't hurt to talk to an engineer as well. One final point on the structural issue: I'd advise you to install a WRB on the exterior side of the Z-girt to minimize water penetration.
When it comes to the thermal issue, the answer is clear: steel furring strips are thermal bridges.
David,
There are a few products on the commercial market that are designed to minimize the thermal penalty of the traditional z-girt that may be of use in your situation.
http://www.cascadiawindows.com/products/cascadia-clip
http://smartcisystems.com/wp-content/uploads/2016/09/GreenGirt-Clips.pdf