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How to Prevent Wood Floor Gaps

White and blue kitchen with medium brown luxury hardwoods

When gaps appear between boards in your wood floor, should you be concerned?  What amount of movement is normal?  Will the gaps close up without intervention? These questions get right to the point of whether you’re going to live with gaps or do something about them.

Gapping mostly shows up in wood flooring during the wintertime. As the temperature drops outside so does the relative humidity (RH) inside our homes, especially when combined with running the central heat.

Decreased RH can lower the moisture content in hardwood floors, causing the boards to shrink. In most flooring, this is observed along the long edges of the boards. Gaps may also occur in the end joints, though it is less common.

Graphic header about how keeping a house's temperature and relative humidity levels in the ideal range can prevent gaps in hardwood floors

Prevent Gaps by Always Staying Within Range

Industry standards suggest that wood flooring should be kept at temperatures between 60° and 80° and RH between 35% and 55%.

To be safe, target the middle and avoid the extremes – 70° and 45% RH are ideal, if you can maintain it.

Maintaining your home at these conditions keeps your wood flooring stable and still.

When conditions fluctuate outside the recommended range, your floor shrinks or expands at a greater rate. In dry winter months, this results in larger gaps between wood flooring boards.

However, if the temperature and relative humidity fluctuate no more than 10% from mid-range, your floors will move very little, but will still be within the acceptable range. We call this an “acceptable gap” in hardwood floors, because they are seasonal and will close when the humidity increases.

Graphic showing ideal ranges for the house temperature and relative humidity levels

Additionally, it’s important to know that your flooring width plays a big role in how much movement occurs. Wider boards (especially over 4″) will move much more than a narrower board.

The rule of thumb: the wider the flooring is, the larger the gaps will be. The narrower the boards, the smaller the gaps.

Graphic header about how gaps can be prevented with a humidifier system

How a Humidifier Can Prevent Gaps

In sections of the country where the winter temperatures dip below freezing over several months, additional humidification is necessary.

This is best accomplished with a furnace mounted whole-home humidifier unit. Once the system is installed, tested, and operating correctly, humidity levels can be controlled and kept within the recommended range.

Without a whole-home humidifier, you are certain to see larger gaps develop and expand throughout the heating season.

Graphic header about what to do in the summertime when theres gaps in your hardwood floors

What if there are gaps in the summertime?

As we roll into late spring and the dry hot summer, humidity will increase and result in floor gaps slowly closing up. When this occurs, it is considered an acceptable, normal wood floor gap.

If the gaps remain throughout the summer, it may be necessary to contact a flooring professional or NWFA inspector to further investigate.

Real hardwood floors show the natural beauty and warmth, connecting the homeowner organically to the land and a centuries-old trade. Being educated about how to care for this natural product will make you and your floor happier.

Download This Guide

Download a free PDF of this article for a quick reference about how to prevent wood floor gaps.


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