Zip system R sheathing

eightinchnails | Posted in General Questions on January 28, 2014 11:16am

I am in climate zone 4- Portland, OR

I would like to do a 2×6 wall, cellulose or fiberglass batt insulation, zip system r sheathing rain screen and cedar siding.

My question is by puncturing the foam under the sheathing am I losing the value that I am trying to create by having a layer of foam.

Thanks for any insight. Cheers

Answer

GBA Prime

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mackstann | Jan 28, 2014 12:33pm | #1
This thread explored the topic and, after a brief scare, it was determined (see comments #17, #21, #29) that the reduction in R-value is insignificant -- perhaps somewhere between .03% and 2%.
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Dana Dorsett | Jan 28, 2014 02:12pm | #2
With shingles nailed directly to the ZIP you'd be running nearly an order of magnitude more nails than with clapboards, and you'd be at the high end of those estimates.

But with Zip-R the foam is on the interior side of the OSB. There's no fastener retention advantage to nailing any deeper than the thickness of the OSB anyway, so going with reasonably short nails that won't fully penetrate the foam, the nail points are all thermally-broken, and the hit would be small. This presumes your rainscreen approach is a plastic mesh such as Obdyke Rainslicker.

With a rainscreen formed with 1x furring held on by timber-screws 24" o.c. the siding nails wouldn't penetrate the foam at all, and the only thermal bridging would be the timber-screws, which is miniscule.