I’ve just inspected a property with thin plywood siding in a minimal configuration.
Your thoughts welcome.
It’s a two-story light construction home built 1982 or 1989, with permits, by the owner, in an earthquake zone. The siding is either thin plywood bare on the studs, or 5/8" type X drywall then ply on the lot line walls for fire rating. There is no WRB or house wrap.
The nail heads on the siding are largely rusty.
I’m uncomfortable with the water unprotected gypsum.
I’m evaluating issues of the thickness of the siding vs. potential quake forces, and the shear value reduction given the drywall layer. I’m sure the gypsum reduces shear valve.
Is it possible there is cross bracing or bridging which is not visible that would increase the strength?
“This method of construction maximizes the weight of the load a structure is able to support. It is a usual application when constructing earthquake-safe buildings.[1]”
Without x-ray vision, I can’t be sure.
Well, I’ll take that back: no. For cross bracing to be effective it would need to be symmetrical, and one corner does not have it. There are no metal (tension) straps, no diagonal cross braces. And for good measure, no mid-wall fire blocking either. Here’s an exposed inside corner at the ground floor level:
Even that would beg the question: how insubstantial could the sheathing be, on a cross braced home? Does code address that issue (outside of a SE’s calculation)?
I was there more than once. The thin cladding was a red flag on the first visit, but there was no way to determine what’s behind. A followup visit is during demolition of a corner (pictured), and reveals it’s just the drywall, no sheathing.
