Upper Side Chambers: The Rest of the Story

EARLIER THIS MONTH, I described my plan to open up two normally enclosed chambers at the junction between the sanctuary roof, ceiling, and walls. Well, that plan was enacted yesterday. We learned a few things, and we took some action! This post describes what happened, and the outcome.…

Looking eastward toward the viewing port
that Ruben and I had peeked through last week

Access Holes

We cut 6 access holes in the troughs along the long walls. These eventually enabled the termite inspector to crawl (often on his belly) the entire length of the chamber on each side.

Pulling up nails in the plywood, after having removed the bitumen membrane

Exposing the plank sheathing, after having removed the plywood

Access hole after the sheathing was removed

Roof Construction and Seismic Integrity

The roofing contractor, upon seeing the construction details that were revealed in the process of opening the access holes, volunteered his opinion that this roof was very well designed and built, and structurally speaking it appeared to be solid overall.

Previously I wrote about the unsettling opinion expressed in the 2003 Historic Structure Report that our sanctuary building would be dangerous in an earthquake because the roof lacked a stabilizing layer of plywood. However, above in the photos you can see for yourself that it does indeed have the desired plywood layer! Furthermore, in order to confirm that this layer extended throughout the roof (not only along the side troughs), the roofer kindly cut out a 4"-square patch of membrane from the barrel vault, revealing the plywood there, as well.

Establishing the presence of a plywood layer throughout was a great relief to me, not only as a safety issue, but also because otherwise the cost and logistics of adding such a layer would be considerable. 😎

UPDATE 8/29/22:  It’s not enough to have plywood in place. It also needs to have been installed properly. The structural engineer in retrospect says that we should have observed the nail size and nailing density pattern, in order to know whether the plywood is actually able to distribute seismic forces to the building walls. Unfortunately, we didn’t make a note of those two factors. (Minimally, they should be 10d nails at 6" on center.) By the time this aspect was called to my attention, the roofers could no longer recall what they encountered. So I suppose we will need to wait the expected year or two until the roof membrane needs to be replaced (or covered over). At that time, we can expose a section of plywood to observe the nails. (This needs to be done anyway for termite treatment; see below.)

Termites?

As I noted above, the termite inspector crawled the entire length of the chamber on each side, tapping on wooden members as he went. He found termite infestations on both sides. Here are three of the photos he provided (click/tap to enlarge).…

Well, we were prepared for this eventuality! Within the hour, the inspector had received authorization (and a price was negotiated) to treat the affected areas. He and his colleague promptly did so, with Premise® foam, a termiticide. 

Their work carries a 2-year warranty. But truth be told, I’m not planning to open up these remote spaces again to check for lingering termites anytime soon. (Except for certain areas where there is good reason to open them up anyway, as described in the next section.)

Structural Damage from Termites?

Significant structural damage from the termites was actually quite limited. The most affected area is in the northeast section — a couple of stretches of both the inner and outer top plates. (If I understand correctly, that term refers to the horizontal members that support the 2 x 4 rafters that form the top of the chamber — and therefore also serve as the joists for the roof troughs.)

Here is a map of the three spots (circled) where the inspector said repairs are needed.

He explained that the chambers are too cramped to allow the termite-eaten lumber to be replaced from the inside. So I believe that it’s best that we wait the expected year or two until the roof membrane needs to be replaced (or covered over). At that time, we will need to pay the roofer to open up those sections of the chambers and then replace the bad lumber. (The inspector insisted that this can be done without having to remove and replace the 2 x 4 rafters themselves.) Now we can plan ahead for that effort, as part of the re-roofing project cost.

Structural Damage from Water or Dry Rot?

With respect to structural damage, our test results were inconclusive. On the one hand, happily, we saw no visible evidence of structural damage from water intrusion or from dry rot. On the other hand, we found nothing that would help to explain the cause of known problems in the past, namely, the various kinds of interior damage to walls and ceiling. 

Largely we were constrained by surprisingly limited visibility; we were unable to see close enough to where the damage was evident from inside the sanctuary — even though we knew we were directly above those damaged areas. It turned out that these side chambers were actually well above those interior surfaces. 

The structure is as follows. The diagonal sheathing that is, in effect, the floor of these side chambers rests atop 9-inch rafters. On the underside of those rafters is the type of lath known as button board (a/k/a rock lath) that two layers of plaster have been applied to from below, comprising the sanctuary ceiling. From above, however, we could only rarely see through to the top of the button board — really only where there happened to be a knot-hole in the sheathing.

In addition, there seems to be a height gap of a foot or more between the bottom corner of the chambers and the level of the tie rods (where the interior walls meet the ceiling).

Closing up and Sealing the Access Holes

By this afternoon, the roofers had closed and patched over the temporary access holes. 

In conclusion, they served a couple of useful functions, mainly in enabling us to arrest several hidden termite infestations.