Gaps in wood flooring

Gaps are a normal part of a solid wood floor. The gaps show movement of the structure or shrinkage of the boards. Often a building will have main supports that create "hinges" within the structure. These flex points lead to gaps in the surface flooring since the structure is moving underneath the floor. This is common in large homes or in homes with a room or a section that sticks out from the rest of the structure.

Gaps that are consistent throughout the floor show shrinkage of the boards after the installation. This shrinkage is normal for some woods and less common for others. Wider boards also show more shrinkage since there are fewer board edges to show the change of dimension. Conversely, narrower boards have smaller gaps since the shrinkage is split among more board edges. The cut of the wood also makes a difference on the dimensional change. Plainsawn wood expands and contracts more in width so it shows more gaps. Quartersawn wood changes the most in height so it will show more unlevelness but less gaps. Uneven gapping can also occur in areas of higher heat and lower humidity such as near vents. Any gaps are showing a dimensional change due to moisture content change within the boards. Increasing the moisture content of the wood is the only way to decrease gaps caused by low moisture.

Gaps can also occur due to uncommon circumstances such as water damage leading to edge crush, or foreign woods that are kiln dried to meet climatic requirements other than those seen in the midwest. First of all, edge crush results when a wood floor absorbs moisture and the boards crush themselves. Once the boards dry, the edges do not spring back to the original dimension since the wood cells were crushed and flattened. Then gaps show instead of the original board width. Gaps can also develop in some wood floors due to foreign woods that loose moisture quicker than they gain moisture. Some of these woods are dried to 8% but they will still shrink and remain in the smaller dimension no matter what humidity the wood is exposed to. These woods require unique acclimation and moisture checking that is different than domestic woods.

Most of these issues are avoidable, but you must deal with professionals that have real life experience with all of problems. These pros know more than what is printed and available to the public. The NWFA has a list of members and most members have the knowledge or they know where to turn to solve or prevent these problems.