Fire rating increase with Denslgass over OSB – am I in for a drying/perm problem?
In planning a wall assembly on a new home, we’re tasked with adding some fire resistance to the wall assembly while not significantly expanding the wall thickness.
By adding a layer of Denslgass /fire rated heating sandwiched between the OSB (Zip in this case) and the cladding, it seems as though we would be reducing the perm rating on the OSB. And this would create a massive issue down the road should the OSB generate condensation on the interior side of the sheathing. (We’re not in a humid climate – this is in Southern California, nonetheless weird weather happens)
We’re thinking of adding a rain screen mesh between the OSB and Densglass.
Any input is highly appreciated.
cheers,
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Replies
Dens glass sheathing is highly permeable, many times more permeable than OSB. No issues with adding it over the OSB, it won't trap any moisture.
I would check with your local codes. Ours allows gypsum sheathing on its own, so you can skip the OSB and install directly on the studs. There are also gypsum sheathing products with WRB pre-installed similar to zip.
Generally you install strapping over the gypsum and nail your siding to that. You can also skip the strapping but you have to nail siding into the studs.
Thanks for the fast reply. So, if the sheathing is looking to dry to the exterior, the Densglass would allow for drying through it. My fear was/is the sandwiched pieces reduce the drying capacity of the OSB.
It's a matter of adding shear wall with the Strcut 1 sheathing where we build.