Q: I have a house we recently bought. It’s older built in 1920 and some of the flooring has dips. It’s not horrible, but what could cause this? Is it something that should be addressed immediately?
A: Very old settling of the building for one thing. Also, the sub floor is probably individual pine planks installed diagonally. It is not at all unusual that such sub-floors exhibit ups and downs and general unevenness. They also have a tendency to become loose with soft wood secured with common, straight shank nails.
Sometimes some of this can be corrected if you have access to the underside of the sub-floor from the basement. Shims or braces can be fastened between joists to give support to spongy areas.