Old House Creaks: Wood Thermal Contraction

A simplified side-view of the same real phenomenon: a row of floorboards butted edge to edge, cooling overnight along with the rest of the house. Wood shrinks far more across its grain than along it, so each board's visible width narrows as the temperature drops while its length barely changes. Neighboring boards, cut with slightly different grain angles, narrow at different rates — and since they're pressed together at a seam, that difference has to be absorbed as friction, building stress until it slips loose as an audible creak. Tune the cooling rate, moisture content, grain mismatch and joint stiffness, drag to pan and scroll to zoom, and click a seam to inspect its stress directly.