North star, I don't know. Walls perp. to property line do not need one hour protection even if closer than 5', which is why I am still unsure about the floor and ceiling joist spaces, per my original post. But if I err on the side of caution and decide to make those spaces comply with 1 hour, how do I do it? There is 2x fireblocking at the exterior of each concealed floor and ceiling joist bay. (either as a rim joist or as structural blocking, which I drew on my attachment)...but that does not fully protect the cavity.