Can I use Durarock for exterior sheathing behind a stone Face?
I am building a garage with 2X4’s spaced 16″ on two layers of block in zone 5, only a stones through from zone 6 in upstate NY. Most of the walls will be sheathed with 7/16″ OSB covered with tyvec, a coraplast rain screen, and sided with various LP smartside products. The inside of the stud bay’s for now will not have insulation, yet I plan on using either fiberglass batts, or blown cellulose and sheet rock in the future to finish of the inside. Also at some point I plan on using a small wood stove to heat it periodically to thaw out cars and other things.
On the lower 3′ of the front I would like to have a stone, or manufactured stone face. I was wondering if I could just use durarock cement board as a sheathing behind the stone. I would fasten the metal lath through the cement to the studs for my scratch coat. The cement board would extend down over two layers of block to grade. I would also use a layer of poly as a capillary/vapor break behind the durarock to prevent moisture wicking into the studs. Another detail would be to run the poly to the outside of the OSB above it to prevent a masonry OSB interface. Then overlapping and taping the tyvek over the poly. Also there would be a taped z-flash from behind the lowest siding course to over the stone.
I would think this would be much easier than trying to sandwich a rain screen between two layers of felt paper. The stone could get wet without much worries and everything will be able to dry to the inside of the layer of poly. If moister ends up being driven into the block I don’t think that would be that big of a deal. Does anyone realize some fundamental flaw that I fail to realize? Is durarock cement board allowed as an exterior sheathing or is it’s tensile strength to low? Also could I bond the cement board to the block with mortar rather than mechanically fasten it? Thanks for any input.
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You'd probably get away with using DuraRock as sheathing in climate zones 1 & 2, but the in zones 5 / 6 the risk of freeze/thaw spalling is too high.
I think that it would work fine if you had a ventilated rain screen between the sheathing and the stone, but this would prove a fairly tricky detail with the 2 courses of block. I built a garage about 15 years ago where the framing sat on a 2'high by 8" deep stone/concrete foundation built on an insulated slab. I laid fieldstone inside the form,backfilled with concrete and rebar,and pointed the stone after the forms were removed. Very attractive. It was featured in a Taunton book on garages.(Garage: Reinventing the Place We Park.) Surprisingly,with insulated 2X4 walls and weather-stripped custom built doors, the inside never froze, with no heat.The bottom 2' of the wall(the stone/concrete) was not insulated. Above the garage space was a small apartment that we kept at 45 degrees through the winter, so it got some heat from that I suppose despite the 10" of fiberglass in the ceiling of the garage(floor of the apartment).To go with the veneer approach, google "rain screen for stone veneer" and lots of info will come up. This is a common way to build,often with brick facing, but,again,there is a rain screen. Dana may be right about the Durock, I don't know. I do not think you should have the poly behind the sheathing,especially if you think it would ever be heated often. If heated regularly you'd have the poly as the condensation surface,unable to dry anywhere but inward.There is lots of info on veneer stone on wood walls- usually they don't involve the 2 courses of block. Good luck with your project.