Do I need to retrofit my pony wall retrofit?

[Pultzar]

I live in a 100+ year old house in Seattle. The house sits on a concrete foundation with a 2x6 wood ponywall in the basement.

The basement was recently retrofitted to bring it up to code with regards to seismic activity. This includes covering the pony wall with plywood to help deal with shear. The contractors installed batt insulation in the 2x6 cavities. So in essence I have:

Outside -> wood siding -> fiberglass -> plywood -> Basement Interior

Do I need to be concerned about rot in this configuration? I could remove the batts by putting some small holes in the plywood and yanking it out, but that would be a gross and messy job.

If the batts are okay, should I do anything else to the interior? Spray foam the edges of the plywood? Paint?

Thanks for the advice everybody. I wish I had found this forum earlier.

 

[Dana]

There is no exterior wood sheathing, and the siding is hanging directly on the studs? (That would be a code violation!)

I suspect what you really have is:

Outside | wood siding | #15 felt or housewrap | exterior sheathing, which could be 1x ship-lap or fiberboard or plywood or OSB | fiberglass | plywood | Basement Interior

The plywood interior is already a "smart" vapor retarder, and there need not be any other vapor retarders, though kraft facers (on either side) would be fine. In Seattle the typical wintertime indoor dew points are in the mid to high 40sF, and the average outdoor temperature is about 40F, so there is a modest vapor diffusion drive for moisture to diffuse from the interior to the cooler exterior side of the assembly, but it's not a huge vapor drive.

The bigger rot risk factor is air leakage transporting the humid interior air moisture out to the cooler exterior sheathing via convection, so sealing the seams of the interior side seismic reinforcement plywood is in order. That would have been easier to do when the plywood went up, using a low-adhesion caulk (you can't use adhesives on sheathing for seismic walls since it makes them too rigid.) Painting the plywood with a decent quality latex/acrylic primer would be a sufficient bonding surface to air seal it with any housewrap tape. Caulk doesn't cut it between seams of plywood, even though it's fine between studs & plywood, where the caulk is essentially clamped in place. But tapes work fine. For more money there are purpose made tapes for sealing clean unpainted plywood.

Sealing the edges with can- foam is fine.

Painting the plywood is fine as long as it's no more vapor retardent than standard latex, but isn't really necessary. A layer of finish latex over latex primer comes in between 3-5 perms, but the plywood itself is 0.5-1 perms when dry. Should moisture in the wall cavity rise to mold-inducing levels the plywood becomes more vapor-open than latex paint, which would allow the moisture to leave toward the interior.

Kraft facers on batts are also "smart" vapor retarders that become even more vapor-open with humidity, but they're impossible to make air-tight. That's fine if they're next to an air-tight layer such as wallboard or plywood that have been detailed as air barriers.