Gaps in Wood Floors

By Robert Robillard on Flooring

floor border and inlay

Hardwood Floor Gaps

Winter is the time that I get questions about gaps in wood floors showing up in solid 3/4-inch thick, wood floors. Gaps in wood floors are normal, and occur when the wood loses its moisture content. Several factors can lead to its cause.

Humidity Wreaks Havoc on Hardwood Floors

Often “gapping” is a result of flooring that was installed during periods of higher humidity. Months later, usually during the heating season, gaps start to show up. The good news is that they usually close back up. Most times, a seasonal gap, one that that allow a dime to fit into it, will close back up during seasons of higher humidity.

Indoor humidity imbalance can also cause gaps. The ideal humidity level is 30% to 50% and an ideal temperature is 60 to 80 degrees. All the wood in your home will expand or contract as moisture in the air changes. You may also notice that your doors or wood windows will swell and stick during rainy seasons.

Reducing Humidity

Methods to reduce gaps include the use of room or furnace humidifiers. These products work by evaporation of water that is introduced into the environment through the heating system. With more moisture in the air, cells in hardwoods begin to expand.

Large Gaps in Wood Floors

Large gaps in wood floors that do not close up in summer months could be and a result of several factors, such as:

  • Excessive moisture
  • High home humidity
  • Moisture from a crawl space below
  • Flooring located too close to a heating vent
  • Incorrect nail spacing
  • Sub-floor levels or deficiencies
  • Structural house settling issues

For normal gaps, no repairs are needed. Adding filler is not usually a good idea, as it will get pushed out as the wood expands with moisture. Filler will work effectively unless the humidity level is kept constant.

For larger, non-closing gaps, a professional contractor can properly repair floors, please consult a professional to evaluate this for you. The BEST time to repair or deal with wood floors is April or October.

Moisture Testing

Achieving Average Humidity

When installing a new solid floor, its best to determine the average humidity level in the home year round. Your goal would be to achieve this average, allow the wood to acclimate in the home a week or two and then install. The acclimation and installation during average humidity will greatly help to reduce contraction and minimizing gaps. A hygrometer is the best tool to determine your specific job-site conditions.

Acclimation your flooring prior to installation means bringing the new flooring into your home so it can acclimate to the new rooms normal relative humidity. Prior to the flooring being installed the wood planks need to be at, or close to the same moisture content as both the subfloor and the environment the flooring is going to be installed in. The acclimation period can be between 7 to 14 days or longer depending on your region of the country.

Note: Most quality wood flooring is dried during the manufacturing process down to between 6-12% moisture content. Use a moisture meter to test the flooring and the sub-floor to make sure the readings of both are between that 6-12%.

Rift and Quartered Oak

Choosing Stable Flooring: Rift and Quartered Sawn Oak

Choose a flooring material that is dimensional stable is a good start to ensure a tight, gap free floor. I often purchase and use rift and quartered oak which is touted as approximately 30 percent more stable than plain sawn oak flooring.  Solid wider width boards will show more gaps, while narrow strip floors can show less.

Rift and quartered boards rival engineered flooring. These boards will only expand / shrink in thickness (height) and will remain stable from side-to-side (width). They are perhaps the best option for wood floors and electric radiant heat, and also an excellent choice to minimize seasonal gaps, buckling, and so on.

Oak Install

Gap Reducing Tips for Wood Flooring

  • Narrow boards will better accommodate wood’s natural expansion and contraction across a floor.
  • Use quarter-sawn wood for planks wider than 3 inches, for better dimensional stability.
  • Acclimate your wood floor: Wood naturally expands and contracts to reach balance with the relative humidity of its surroundings.
  • Avoid installing wood flooring when moisture levels are high, such as during painting or the installation of plaster.
  • Before hardwood floor installation, operate the heating system until the relative temperature and humidity in the space. Achieve the average level expected for seasonal conditions in the area in which the wood floor will be installed.
  • Ensure the floors moisture content is appropriate for your area. 6-to-8 percent moisture content is average.
  • Reclaimed woods typically have tighter growth rings making them denser and more stable and less likely to shop gaps.
  • Parquet flooring expands and contracts less.
  • Dark floors hide gaps between boards.
  • Flooring with beveled edges make any gaps less obvious.

Rift and Quartered Oak

Problem Areas

There are situations with floor gaps in solid hardwood is a recurring problem. whether a result of the environment, structural issues or humidity issues.  It’s in these situation that I recommend you look at engineered flooring as an option. It is rare that engineered floors have seasonal movement issues..

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About the author

Robert Robillard

Carpenter / Remodeler / Editor

Rob Robillard is “The Concord Carpenter” Rob is a builder, general contractor, carpenter, woodworker, and editor of Concord Carpenter and ToolBoxBuzz As a General Contractor and carpenter, Rob owns and operates Concord Carpenter LLC. A full-service remodeling and construction company. Rob is a recognized leader in home building best practices and a source for how-to information for building professionals. On this website, Rob covers all aspects of home construction, building science, home improvement, woodworking, remodeling, and some of the best product and tool reviews. Rob is in charge of our Tool and Product Review series - Concord Carpenter Videos where we post all of our tool reviews and video tutorials. Rob approaches remodeling and building construction with a pragmatic and problem-solving approach. He enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the construction and remodeling industry. He's a strong advocate for "raising the bar" in the construction trades and promoting the trades to youth. #BeAMentor #Green2Great Craftsmanship, quality, and pride guide his journey on this channel The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob

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