Gapping between your floorboards can be caused by differing humidity levels.
During the cold and dry winter months, floorboards shrink and gaps appear. During the warm, humid summer months, the floorboards expand again. No matter what type of hardwood flooring you have, there will be some changes in the gaps due to humidity fluctuations. To reduce the amount of gapping in the winter, there are a few steps you can take.
You can use wood filler in the gaps, however, this isn’t recommended because it’s only a temporary fix. When your floors expand again in the summer, the filler can pop out and if your floors contract even more in the winter, the filler can fall into the gaps.
For more successful permanent results, choose narrow floorboards. Narrow boards contract less than wider planks. You can also try to reduce ventilation in your home. The drier and cooler the air, the more your floors will gap. Make sure your windows are sealed properly to prevent drafts. Another solution is to use a humidifier during the dry winter months. This will introduce moisture back into the air and back into your floors.