Buildings Are Not Static

It can’t be said often enough that buildings move in various ways, from the effect of environmental conditions. You’ve got gross structural movement from gravity and lateral loads; up, down, and sideways movement from changes in soil volume from water movement; expansion and contraction from temperature changes and water infiltration in the building materials. That last one is worth a photo

from yesterday’s site visit to a very old house with a wood shingle roof. See the light from outside, coming through a gap between two of the shingles? Note that there’s no water staining around there? When it starts to rain, the shakes absorb water and swell, closing the gap. So not only does the building move, it moves in a way that is specifically beneficial.

This may seem like an isolated waterproofing example, but there are similar structural movement. I’ve seen beams that have three supports (at the ends and middle) when fully loaded and two (at the ends) when lightly loaded. I’ve seen stairs that share load (my apologies for the missing photo at the link) as people’s weight transfers from one tread to the next. I’ve seen roof trusses that carry load in different manners when fully loaded and when partially loaded.

Buildings move and it can be to our benefit if we understand how they move.