I’ve typically been using photographs from our field work for these posts, but a picture on another site caught my eye and it deserves recognition. AbandonedNYC has beautiful pictures of buildings left to rot. Despite the name, they are not all in New York. This post contains one of the best illustrations I’ve seen of a building performing when it should have already collapsed: here. The bottom chords of the two gable trusses closest to the camera are literally rusted to the point of disappearance. Note that the upper chords, tight to the roof underside, change from thin near the roof apex to thicker where they have to carry the header purlin that is at the top of the dormer windows.
Why hasn’t hit fallen down yet? This is in Newport RI, a place with significant wind and snow load. The short answer is that the walls are probably heavy enough to take some outward thrust if the roof acts as a gable-folded shell, but that won’t last. Off in the distance, the roof has collapsed at the other end of the building.