My new neighbor in the rental house knocked on my door, distraught. She had gotten up from the couch to get a snack. While she was in the kitchen, her living room ceiling collapsed onto the couch on which she was sitting.
She could have been killed or seriously maimed. I later put a 1’x1′ secction of the ceiling on a scale and it weighed nearly 20 pounds.
Upon investigation, I noticed a few things. First, and most critical, was that the ceiling was composed of two layers of drywall. One was clearly added after the second one, as the nails only penetrated the top layer (technically “bottom” layer, closest to the joist). And yes, the drywall was nailed, not screwed, to the joists. The nails were old and rusted, safe to assume that this first layer was original to the house, dating to 1941. The second layer of drywall had been installed perpendicular to the first layer and the joists.
I also noticed there was a good deal of moisture stains on all of the second floor joists. Stains and drips, indicating there were periods of intense sweating on humid days in this un-conditioned house. It should be noted that this house, owned by the son of the original owner, has undergone precious little change in eighty years; nothing close to a significant renovation but lots of cosmetic patches between tenants. (The house has been a rental for the past 20+ years.)
My theory was that rather than replace or truly repair a continuously cracking ceiling, the landlord or his handyman had laminated (glued) a second layer of drywall on top of the first. Over time, the combination of live loads on the bedroom above and the extra weight of the second layer of drywall worked enough of the nails out of their sockets to cause the collapse, probably aided by the intermittent moisture in the floor cavity.
And then it happened again, a few months later and a few doors down on the same block. Another house built in 1941, another erstwhile rental. Could they have shared the same careless handyman?
No. There was something more.
I have been casually using the term “drywall” as a generic placeholder for prefabricated wallboard, but that is not exactly right. Drywall as it is currently used indicates crushed gypsum plaster, and the top layer did indeed appear to be gypsum, either 3/8″ or 1/2″ thick. This is the layer nailed to the joists in 1941. But the second layer was a different composition– still old, but a more precise rendering would be cementboard, and it was more like 5/8″ thick. This accounts for the unusual weight that pulled the nails out. At the first house I attributed this to further evidence of the clueless handyman. But now a new thought occurred to me: what if both layers were original to the houses?
It makes sense: drywall was a rather new material at the time. Perhaps cracks were appearing in the ceiling in a way that didn’t happen in the more typical plaster and lath of the day? And perhaps the solution by the builder was to glue a second layer of the more rigid cement board to the underside of the already assembled ceiling?
That’s my theory, and my advice for Arlingtonians with houses built around 1941: keep watching the skies, er, ceiling.