Subsidence

Ground sinking — usually clay shrinking as trees or leaks draw moisture out. Cracks typically diagonal, wider at the top, often near corners and openings.

Heave

Ground rising — clay swelling as moisture returns, often after a tree is felled. Floors lift, doors stick at the top, brittle finishes crack.

Why it matters before you extend

A new extension on a site with a history of either problem needs careful foundation design. Tree removal and replanting decisions need to be made consciously, not by accident.