David, for a 1950’s build, I am surprised to see plywood on the roof.
Although I know Maine has always been behind times, plywood was not in use in northern Maine until the late 60’s.
It was very common to tonail members as you saw it and we did not have money to waste to buy perforated pipe straps to aid in the connection.
If the plywood sheathing were original to this building, you would see that the left overs would have been used to provide gussets on the truss chords.
Plywood only really started being used in 1940, and not everyone could afford it.
My recollection is using spruce boards on the roof till about 1962.
Most people kept using boards because it was strong, cheaper and labor was not a factor in those years. Hell, I was working for about 50 cents an hour in those years. :mrgreen:
I believe that since this plywood sheathing was installed, it leaked at one time so much to create all those water stains.
You can see some of the roofing nails that are extra long and some that barely penatrate the plywood.
This indicates to me that there was a re-roof done and the roofing nails were pounded in before the new install.
The knob and tube could be original, but on the other hand were used by many people for supporting miscellaneous wiring. Most knobs were salvaged for whatever else they could be useful for.
I would call out the softness in the plywood and moisture stains and go from there.
Been there that long, it won’t go anywhere.
Hope this helps.