Detailing a Rainscreen with Exterior Rigid Foam Insulation
Here’s the situation. 2×6 frame with 1/2″ OSB. Grace envS WRB over OSB. Planning on 1″ of foam and we’re doing fiber-cement panel siding. At the bottom of the wall we either transition to stucco or to an exposed steel I-beam
Building is in Tucson.
So it seems all the details I see for rainscreens are not over exterior rigid foam, and many of them don’t have a vent layer, and that makes things frustrating. The fiber cement guys say to secure the cement into the wall framing, but with foam, osb and furring strips, you would need a really long nail to hit the framing and provide proper embed. Plus no one talks about the bottom and covering the exposed base of foam. I’ve attached a quick detail over the I-beam to illustrate the problems. So here are my questions:
1. What should I do here as I transition to the I-beam? Ideally I should cover the bottom of the entire wall assembly so I don’t see a hodge podge of OSB, Foam, etc. I’ll obviously have a bug guard for the vents(maybe a cross-ventilated furring strip or a plastic rain-screen vent from Fry-Reglet), but that stops at the foam.
2. If I secure the 1×3 furring strips to the framing with 3″ ring shank nails (or maybe long screws??) , can I just secure the fiber cement to the 1×3?
4. Some systems recommend treating the 1×3. I’ll do it if it’s necessary, but I loathe that copper-green crap..it gives me a headache. And because I’m using aluminum fry-reglet trim I’m assuming I’ll have to cover every single furring strip with a barrier like vycor. So is this necessary?
5. I’ve been frustrated enough to consider scrapping the foam and the furring strips and nail the fiber cement directly over the WRB/OSB. My wife tells me “we’re in Tucson, where it never rains and it’s dry”. Talk me off the cliff…
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