Seasonal gapping — the floor contracting in dry indoor air. Even gaps that close again in summer are movement; uneven gaps that never close are a specification or moisture problem.View full size — Finished oak floorboards with even dark gaps opened between every board after a dry Toronto winter.

Some seasonal movement is normal in solid hardwood and is not itself a defect. Gapping becomes a defect when it is large, permanent, or the result of material that was never equalised to the space.

It is one of the five named failure modes, and it is the one homeowners notice first because it appears without warning in January.

Relative humidityThe amount of water vapour in the air relative to what that air could hold at its temperature — the environmental variable a hardwood floor actually responds to.
AnisotropicDescribes a material whose properties differ by direction — in wood, movement across the grain is significant while movement along it is minimal.
AcclimationThe period during which flooring material equalises to the conditions of the room it will be installed in — a minimum of 72 hours, in the actual conditioned space.
Solid hardwoodFlooring milled from a single piece of wood, typically 3/4" (19 mm), with a generational wear layer and high sensitivity to humidity swings.

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Provenance

Where this definition comes from

toronto hardwood climate moisture protocol — failure modes

Framework pillars this term is material to

Pillar 4 — Expansion and movement

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Seasonal gapping

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