Climate & Local
Wood Floor Gaps in Winter: Why They Open in January
April 1, 2026 7 min read By Fort Worth Flooring Co
Every January we get calls from people who have just noticed gaps between the boards of a hardwood floor that was fine in October. Almost all of them are looking at a floor that is working correctly.
Why it happens here specifically
Wood is hygroscopic, which is a technical way of saying it is never finished reacting to the air around it. Dry air pulls moisture out of a board and the board gets narrower. Humid air puts it back and the board widens again. The movement happens across the grain, not along it, which is why a floor changes in width and never in length.
North Texas has a bigger indoor humidity swing than most of the country. In summer the air is humid and the air conditioning is running, and a house typically sits above 50 percent indoor relative humidity. In winter the heating is on, the outside air is dry, and the same house can drop to 20 or 30 percent.
That is a wide annual range, and solid wood moves across all of it. Boards shrink across their width in January. The shrinkage has to go somewhere, and it goes into the joints between them.
This is genuinely a regional characteristic. On the Gulf Coast, where indoor humidity stays high year round, the dominant seasonal complaint about a wood floor is cupping from too much moisture. Here the dominant complaint is gapping from too little. Same material, opposite failure mode, and it is why advice written for a humid coastal climate can be actively wrong in Fort Worth.
Which gaps are normal
Normal: gaps that appear evenly across the whole floor, in every room with the same species, starting in December or January and closing again by May or June. Wider on wide planks than on narrow strip. Visible but shallow.
Not normal:
- A gap that stays open through July. Seasonal movement reverses; a permanent gap does not.
- Gaps in one area of a room only. That is usually a moisture source or a subfloor problem, not the season.
- Gaps wide enough to lose a coin in, on a strip floor.
- Gaps accompanied by boards that have lifted at the ends, or by a hollow sound underfoot.
The second and fourth are worth having looked at. The first two are worth watching for one full year before doing anything.
Board width is the lever
The wider the board, the more absolute movement it has across its width, and the bigger the gap for the same percentage change.
A two and a quarter inch strip floor gaps by an amount most people never notice. A seven inch plank in the same house, at the same humidity, opens a gap you can see from across the room.
This is worth knowing before you buy rather than after. Wide planks are the look almost everyone wants right now, and they are entirely installable here — but they belong in a house where the humidity will be managed, or with an owner who knows the winter gap is part of the deal. We would much rather have that conversation at the estimate than in February.
Engineered board moves considerably less than solid, because its layers are cross-laminated. If you want a wide plank and you do not want the seasonal gap, that is the honest route.
Why not to fill them in January
This is the mistake that costs money.
Filling gaps when the boards are at their most contracted means the fill is sitting in a joint that is about to close. In July the boards expand, the joint narrows, and the filler is squeezed out — onto the surface, or crumbling, or holding the boards apart in a way that puts stress somewhere else.
If gaps genuinely need filling, it is done nearer the middle of the annual humidity range so the fill is not under compression for half the year. Sometimes the honest advice at a January estimate is to look again in May and decide then.
What actually reduces it
Holding indoor relative humidity in the 35 to 45 percent band year round narrows the swing the floor experiences. That means a whole-house humidifier run through the winter, not a portable unit in one room for a fortnight.
It is worth doing in a house with a wide-plank solid floor. It is usually not worth doing for a strip floor that gaps a little and closes again, which is behaving the way the material behaves.