· Michael Blair
Solid hardwood takes on moisture in a humid Nashville summer and gives it back in a dry heated winter, and it changes width as it does. Gaps that open in January and close by July are the floor behaving exactly as wood behaves.
What normal movement looks like
Thin, even gaps distributed across the floor, appearing in winter and closing in summer. On a wide-plank floor they are more obvious simply because each board moves more in absolute terms.
A useful reference is a gap you can see but not catch a fingernail in. Movement of that order across a room is ordinary in Middle Tennessee.
What is not normal
Gaps that stay open all year, gaps concentrated in one area rather than spread evenly, cupping where board edges rise above the centre, or crowning where the centre rises above the edges.
Any of those points at a moisture source rather than seasonal humidity — a crawl space, a plumbing leak, or a slab that was not tested before the floor went down.
- Even seasonal gaps: normal
- Gaps that never close: a moisture or installation issue
- Cupping: moisture from underneath
- Crowning: often sanding a cupped floor too early
- Localised gapping: look for a leak nearby
The crawl space connection
Much of Nashville’s housing stock sits over a vented crawl space, and in summer humid outside air condenses on cool surfaces down there. That moisture rises into the subfloor.
Encapsulating or at least sealing and dehumidifying a crawl space stabilises the floor above it more reliably than anything done to the floor itself.
Managing indoor humidity
Wood is happiest in roughly 35 to 55 percent relative humidity. Middle Tennessee summers run well above that and winter heating pulls it well below.
A whole-house humidifier in winter and dehumidification in summer narrows the swing. Even a modest reduction in the annual range visibly reduces gapping.