Hardwood flooring, as the name suggests, is a natural product. While wooden flooring is a beautiful addition to any room, adding value and transforming the look and feel of a home, the fact that it is a natural product means that it can undergo changes. Wood responds to humidity levels and moisture in the air, and this can cause your hardwood flooring to expand or contract.
Wood is a hygroscopic material, meaning it has the ability to attract and hold water molecules from the air surrounding it. When exposed to the air, wood will attract or release moisture until it is at the same level as the surrounding atmosphere. So if there is excess moisture in the air, your hardwood flooring will attract some of this moisture, causing it to expand. If there is less moisture in the air, wooden flooring will release some of the moisture held within it back into the air, causing it to contract and shrink.
When wood goes through this change, it may not expand or contract equally in all directions. This expansion and contraction is completely natural, and as long as the movement is not too extreme, you should have no need to worry. There are some steps you can take to try and limit the movement of your wood flooring, however.
During the cold winter months, your home will be heated, causing the air to become dry and humidity levels to drop. This can cause your hardwood flooring to release moisture and contract, causing small gaps to appear. To limit this, try to keep the humidity levels in your home between 50-65% using a humidifier, or by placing damp tea-towels on your radiators.
Over summer, when the temperature is higher, humidity levels can rise considerably. This, in turn, can cause your wooden flooring to absorb the excess moisture in the air and expand, pressing the boards against each other. To stop this from happening, leave your windows open for a short period each day to allow the humidity to leave your room, being replaced by fresh air circulating instead.