Stone veneer over Zip sheathing
user-6651407
| Posted in General Questions on
I’ve read a few articles on stone veneer, and see the statement that stone veneer on OSB is one of the riskiest wall assemblies. Is this referring to having no WRB and rainscreen?
We are in Climate Zone 5, have ZIP, but will also use Asphalt Felt and Rainscreen.
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Replies
In my opinion people are speaking about adhered stone veneer (i.e. attached via adhesive to the sheathing) vs stone cladding, Stone cladding is similar to brick cladding with its brick ties and ventilation gap.
Bridget,
In my opinion, both types of cladding -- adhered manufactured stone veneer and stone veneer with brick ties -- are risky over OSB. There are many, many reports of failures.
A water-resistive barrier (WRB) is not optional. WRBs are required by code.
If you insist on installing stone veneer over OSB, you should certainly include a ventilated rainscreen gap. Omitting the rainscreen gap increases the risk by an order of magnitude.
-- Martin Holladay
Bridget,
In both cases you need a ventilated rain screen gap along the entire backside of the veneer. The WRB layer isn't sufficient to prevent moisture intrusion. Don't expect the stone 'cavity' will naturally be clear and constructed for airflow - this cavity is used by masons to accommodate variations in the stone veneer to keep the front of the veneer in plane, reinforce the stone with additional mortar, etc.
In the case of adhered stone, think of it as "lumpy stucco" and to paraphrase Martin, "To Install Adhered Stone Right, Include an Air Gap".
A link to a quick video on adhered stone rain screens https://www.youtube.com/watch?v=864GV-bTuiM
A detail showing the full stone system with a ventilated rain screen is available at https://www.mtidry.com/hyperspecs/full-stone-at-bottom-of-wood-framed-wall
Martin:
Would you still see this as risky over Zip sheathing with a rainscreen(something like the MTI product )? If so, what is a better alternative when doing stone?
Kevin,
Stone houses in France and Italy are beautiful. If you want to build a stone house, build a stone house.
If you are building a wood-framed house sheathed with OSB, it makes no sense to try to make your wood-framed house look like an old house in France or Italy. Embrace honesty. It's a wood-framed house. Choose an appropriate siding like cedar shingles or fiber-cement lap siding.
-- Martin Holladay
Do you feel the same about brick?
Kevin,
For a variety of reasons, brick veneer is less likely to result in a wet-wall disaster than stone veneer. That said, I've read about a lot of wet-wall disasters in wood-framed homes with brick veneer. (For more on the topic, see my article, Flashing Brick Veneer.)
Philosophically and aesthetically, I'm averse to the idea of trying to make a wood-framed building look like a stone or brick building. What's wrong with accepting the aesthetic of a traditional wood-framed building rather than trying to disguise it with deceptive cladding?
Perhaps the biggest sin is the stone-clad dormer. What are these stones sitting on? They're floating in midair, with no foundation, violating the laws of gravity and masonry.
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