Can stone veneer be applied to polyiso foam board?
Bubba52me
| Posted in Green Products and Materials on
We are building a new home, our forever home. We are adding 1 inch, Polyiso foam board, foil backed on both sides to the exterior of the home under the siding. We want stone veneer on the bottom of the house up to the windows. Can stone veneer be applied to the Polyiso foam board? Thank you so much for any and all of your advice and suggestions!
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Replies
Best practice is to include a rainscreen air gap behind the stone veneer with a weep system at the bottom - either stone cavity weeps on the stone ledge or a ventilated weep screed if it's an adhered stone veneer. There is nothing detrimental about the stone veneer to the foil faced insulation (or vice versa) but you will have to answer the old questions about which layer of your wall serves as the WRB, whether your insulation profile is climate appropriate, and whether vapor barrier created by the foil faced polyiso causes any concerns with an interior vapor barrier. Sharing your climate info and other details of your project are important for this discussion.
Tyler
We are building in Western Pennsylvania. I believe climate zone 5. We have 2x6 exterior walls with 1/2inch osb. The interior walls will be insulated with the required r value fiberglass insulation. The exterior will be finished with manufactured stone up to windows and then vinyl siding
Bubba,
The company with the best products and materials appropriate for stone veneer is MTI.
Check out their web site. Two details are attached below. I know these details don't show rigid foam, but these details can be easily adapted to include rigid foam.
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Bubba,
If you are in Zone 5 and have 2X6 walls, you want a minimum of r-7.5 on the exterior. That is more likely with 1.5 inches of polyiso. See Martin's article for detail: https://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing
Also... If you are looking at cultured stone for the facade...
Matt Risinger recently posted a video on a new product called Certainteed Stonefacade. It uses a stainless hanging system to greatly reduce installation time. Of course, you should do more research since I don't have any experience with this system.
Steve has it right. A 2x6 / R20 is code minimum from a thermal performance point of view, but if with exterior foam it needs a minimum of R7.5 for dew point control at the sheathing:
https://up.codes/viewer/utah/irc-2015/chapter/11/re-energy-efficiency#N1102.1.2
https://up.codes/viewer/wyoming/irc-2015/chapter/7/wall-covering#R702.7.1
With only 1" of foam it will will be less resilient to air leakage from the interior side and would need a reliably class-II vapor retarder on the interior side. With 1.5" of polyiso it keeps the average wintertime temperature of sheathing warm enough to not need more than standard latex on wallboard for an interior side vapor retarder.
If that extra half inch of depth is too precious, using an inch of rigid rock wool instead of polyiso is somewhat lower thermal performance, but would offer enough exterior drying capacity to meet the "Vented cladding over wood structural panels." exception for zone 5 that would allow use of standard latex paint as the interior vapor retarder.
You would have to consider shear strenth of the lath fasteners through the foam. The stone is bonded to the lath, the lath is basically hanging since the felt layers do not allow any sort of bond to foam which would be useless anyways, unless you have a foundation ledge.
A lighter weight clip system might work good. Someone mentioned one brand, I like Nichia's.
If I had a nickel for people claiming forever homes and then selling them.
Have you looked at the EnduraMax wall system, which incorporates polystyrene panels (R-9) molded to accept masonry units? To finish the wall, the joints are then mortared. The panels are attached to the substrate with specialty fasteners and the system is engineered to support the weight of the faux stone inserts.
https://www.echelonmasonry.com/performance-upgrade-options/enduramax-high-performance-wall-system