Real hardwood is a natural material that takes on and gives off moisture with the air around it. When indoor humidity swings too far, the wood moves: it swells and cups when the air is damp, and shrinks and gaps or cracks when the air is dry.
The target range
Most solid hardwood is happiest in a relatively stable indoor environment — commonly cited as roughly 30–50% relative humidity and a consistent room temperature. The exact range depends on the species and the manufacturer's guidance, but stability matters as much as the number.
How to keep it stable
- Run a humidifier in dry winter months and a dehumidifier or air conditioning in humid seasons.
- Acclimate new wood in the room where it will be installed before laying it.
- Avoid big, sudden swings — leaving a home unconditioned for long periods is hard on wood floors.
Watch the seasons: a small amount of seasonal movement is normal. Persistent cupping or wide gaps usually point to a humidity problem worth correcting before it permanently damages the boards.
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