Every winter, we get calls from homeowners worried about gaps between their hardwood boards. Every summer, we get calls about edges of boards rising. In most cases, both are the same thing: wood responding to Central New York’s big seasonal swings in humidity.
Why Wood Moves
Wood absorbs moisture from the air and releases it when the air is dry. As it does, boards swell and shrink — mostly across their width. A typical oak floor can change noticeably across a room between a dry February and a muggy August. That’s normal. Problems come when the swings are extreme or when moisture comes from below.
Winter Gaps
With forced-air heat running, indoor relative humidity can drop below 25%. Boards shrink and gaps open, sometimes about the thickness of a dime. Wider planks show wider gaps.
- Normal: gaps that appear in winter and close in late spring.
- Not normal: gaps that never close, or boards that crack or split.
- Fix: a whole-house or room humidifier to keep humidity around 35–55%.
We generally don’t recommend filling seasonal gaps: filler can crack out or get pushed up when the wood swells in summer.
Summer Cupping
Cupping means the edges of each board are higher than the center. It happens when the bottom of the board takes on more moisture than the top.
- Common causes: high summer humidity, a damp crawlspace or basement below, a plumbing leak, or floors installed without enough acclimation.
- Fix: find and eliminate the moisture source, run dehumidification or air conditioning, and give the floor time. Mild cupping often flattens out as the wood dries.
- Don’t sand it too soon. Sanding a cupped floor before it dries can leave boards crowned (higher in the middle) once they settle.
Crowning and Buckling
Crowning — boards higher in the middle than at the edges — often follows a cupped floor that was sanded too early, or moisture reaching the top of the floor. Buckling, where boards lift off the subfloor, usually signals a serious water event. Both need a professional look.
How to Keep Floors Stable
- Keep indoor humidity around 35–55% year-round. An inexpensive hygrometer tells you where you stand.
- Run a humidifier in winter and air conditioning or a dehumidifier in summer.
- Keep basements and crawlspaces dry — they affect the floors above them.
- Make sure new flooring is acclimated and installed with proper expansion space at walls.
- Consider engineered hardwood for wide planks, radiant heat, lake homes and seasonal homes.
Lake and Seasonal Homes
Homes on Skaneateles, Owasco and Cazenovia lakes, and any house closed up for part of the year, see even bigger swings. Keep some climate control running when you’re away rather than shutting everything off.
If your floors have gaps, cupping or boards that just don’t look right, we’re happy to take a look. Learn about our refinishing and repair services.
Talk to a Local Flooring Pro
Every home is different, and the best answer comes from someone looking at your actual floor. Crow Hill Hardwoods has been installing and refinishing floors across Greater Syracuse since 1992. Request a free, written estimate, call (315) 246-4425, or stop by the showroom at 2 W Main St in Marcellus, Monday–Friday 10am–4pm.
