Exterior foam wall sheathing vs flash & batt
I saw an article by Steve Easley about changes coming in the 2021 IRC for wall insulation and I’m wondering about what current options are going out the window. Any insight from fellow GBA readers would be appreciated.
Continuous exterior insulation on walls – I’ve been using flash & batt on walls and it works great, even though there are still thermal bridges at studs. The effective total wall insulation is more than adequate. It makes for an airtight wall. And vapor control works in all climate zones. My designs are stock house plans that can be built in any climate zone, so I need solutions that require only minor adjustments between zones. Flash & batt fits the bill.
A downside of exterior foam is the complications it adds to waterproofing door and window openings (significant labor expense), as well as installation of heavier exterior finishes such as cast stone veneer and stucco.
An alternative is Huber Zip-R sheathing, IF it can satisfy shear wall requirements for seismic zones. I don’t like to use vendor specific products though. Other companies need to start producing similar panels.
What are your thoughts with regard to 2021 changes and the above?
Will flash & batt still be a code viable solution?
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Continuous exterior insulation is always going to have the advantage of reduced thermal bridging over anything you do between the studs. That's it's primary advantage. If you're using 1" foam or less, those trim details aren't too bad. Over 2" of foam is where the trim details really become more of an issue (so called "thick" exterior foam).
Huber has tested their products for shear walls. As long as you follow their nailing scheduled exactly, you're installation should perform up to their specs. I admit the thicker sizes of Zip-R look odd to me too, but Huber has the engineering info to back up their claims.
I can't speak to the upcoming code revisions since I haven't looked into those yet.
Bill
> Will flash & batt still be a code viable solution?
Yes. In some cases, it also allows it to be thinner.
If you otherwise meet code racking requirements, you are free to make your own Zip like assembly (foam between studs and sheathing, fully adhered WRB).