Wood movement, checking, and color change

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What's normal (surface checks, color variation, mild creaks) vs. concerning (full-thickness cracks, splits across the grain, soft spots).

The wood in your sauna will move. Heat-treated timber is dimensionally stable, but no wood is perfectly inert. Some movement is normal and expected.

Normal characteristics

Small surface checks (hairline cracks running along the grain) on bench tops and wall panels. These appear within the first few months and don't grow significantly. They're cosmetic and don't affect performance.
Minor color variation between boards. Wood is a natural material and grain patterns differ.
Slight shrinkage and expansion with seasonal humidity changes. The cabin may feel marginally tighter or looser at different times of year.
Mild squeaks or creaks from the cabin during heat-up and cool-down as components expand and contract.
Untreated wood weathering to a soft silver-grey on outdoor exposure over years.

Cracks that go through the full thickness of a panel (visible from inside and outside)
Splits running across the grain (against the wood fibers, rather than along them)
Visible gaps between panels that weren't there originally and grew over a few weeks
Soft, spongy areas in any wood surface (could indicate moisture damage)
Discoloration or dark stains that appear without an obvious cause

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