DIY make your own Zip R6 sheathing?
I recently saw a video in which the GC was creating pseudo Zip R6 panels using GP Force Field with a 1″ Polyiso panel glued to the back of the osb panel. He had a team member gluing them up into a big stack of sheets for the carpenters to pull from as they worked.
At $21/sheet for the Force Field and $16 per sheet for the rigid foam ($37 total) , this is a meaningfully cheaper alternative to the current $80 per sheet for Zip R6.
Has anyone seen something like this accomplished before? While it is additional work to glue the two parts together prior to sheathing the house, it seem like it would still be less than a full two step process of installing the sheathing, and then installing the rigid foam over the sheathing, adding window bucks, etc.
Any thoughts as to if this is a thoughtful solution to achieve a Zip R type product when the budget otherwise wouldn’t allow, or just a disaster waiting to happen?
Asked through the lens of a Zone 4 residential project.
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Replies
The problem is what you have described is not one of the preapproved assembly.
The only way the plans should get approved with that assembly is with an engineer’s stamp on the plans.
Zip did a ton of testing and has the numbers to prove their product is “strong enough”. You don’t have that testing and it seems unlikely an engineer is going to take on the risk and put his stamp on the plans for less than you can buy the Zip.
Seems to me you would have much less labor and materials and a stronger building if you put the foam on the exterior and worked thru how to attach the siding thru the foam .
Walta
Assuming the OSB is being used for bracing/shear value, then yes, that's not a code approved prescriptive solution, does not have an ICC-ES report for use as prescriptive bracing or engineered shear walls, and its very doubtful an engineer would stamp the plans with something unproven.
In the unlikely event the wall bracing is being provided by another method (Let in brace, Gypsum, or perhaps partial sheathing which is then accounted for with various depths of foam) so the forcefield is only being used as a WRB and as a nail base for siding, it should be a viable option, although I could see it raise some eyebrows when the inspector comes by.
Your assumptions are correct. The osb would be providing bracing/shear strength. Thanks for your insights!
Good observations. I guess with the Zip R, you are paying in part for their testing and certifications to be used for shear strength.
I guess that I am back to osb with the foam on the outside. Here in VA, continuous insulation is mostly unheard of, so finding subs willing to learn a new process is difficult.
That is exactly what you're paying for: an engineered product that has been tested and certified to perform as indicated in a certain situation. Huber did all the work for you, you just have to install the product and you're good to go.
Why not just put the insulation on the exterior of the sheathing panel though? That way you have nothing to worry about since the structural part of the panel is done in the usual way -- directly against the framing. Rigid foam on the exterior of the structural sheathing is the usual way to put these assemblies together in the field, and it accomplishes the same thing as Zip in terms of adding R value. If you use foil faced polyiso, that foil facing can double as your WRB if you tape the seams.
Bill
Alternative product
https://lpcorp.com/products/panels-sheathing/insulated-sheathing
The difference between this Nova Core product and Zip is that the exterior of the Zip has a waterproof green layer on it. This stuff appears to be exposed OSB on the exterior side.
ZipR approx $80 per sheet
NovaCore approx $45 per sheet
https://www.youtube.com/watch?v=7urzGiSLbjo
I'd rather waterproof the exterior than trying to make my own laminate.
Likely a patent issue with using the WeatherLogic coating on the NovaCore panel. Seems like an easy competitive product if there were no roadblocks.