Eli5 What is happening when a house “settles.”
In: 3
Lots of processes are involved.
Over decades, the house’s foundation can shift due to freeze/thaw cycles or other moisture changes in the surrounding soil. This is the least likely cause but the most serious should it happen.
Houses built from actual cut lumber (as opposed to lam-beams and particle board) will shift as the wood structural members dry and shrink. The shrinkage will be up to half a half percent over 50 to 100 years. That doesn’t sound like much, but it means a twelve foot joist will lose about 1/2″” in length over time. This is no big deal if the house was built with the shrink in mind (most are). That said, anything tied to such a beam will have shifted or cracked. Any staircase will include two or three long pieces that will also shrink, resulting in sagging, creaking, split treads, and the like. A house with stairs or a service chimney is most likely to shift nearby.
Standing right now in the basement of my own house, built in 1929, I’m able to see two joists that cracked in the middle. It’s a result of them becoming brittle with age and having flexed under foot for nearly 100 years. So that’s another failure mode.
This is all said assuming the homeowners have followed Baller’s First Law of Building Maintenance: Control where the water goes. If the building envelope is compromised, all bets are off in regards to the structure staying up.
Latest Answers