Gaps in Wood Flooring- Are they Normal or Abnormal?

Gaps between strips in wood flooring is a common complaint. Often these gaps occur because of normal, seasonal conditions. However, occasionally gaps appear because of improperly manufactured or installed flooring.

Normal Gaps
“Normal gaps” (sometimes called “cracks”) may occur seasonally-these gaps close during the higher humidity seasons or the non-heating season  Normal gaps may vary in width from “hairline” gaps to more significant gaps (up to or greater than the thickness of a quarter) depending upon the width of the strips of flooring. Larger gaps are expected in geographical areas associated with an extended dry heating season, Plank or strip floors sometimes “panelize” due to movement of under-floor construction and reflect gaps directly associated with the sub-floor movement.

To further complicate matters, normal wintertime seasonal shrinkage may be concentrated into only a few gaps if the finish glues individual boards into panels. Other joints between these larger gaps generally remain tight. In this event, some gaps may be considerably wider than the thickness of a quarter but still considered normal if the larger gaps nearly close during the more humid season.

Because of widths involved, plank floors, can shrink individually up to three or more times as much as a 21/4″ wide strip floor. Therefore, normal, seasonal gaps found in those floors can be much larger than in a strip floor. Again, if the floor expands so that gaps disappear during the humid non-heating season, they should be considered normal.

Abnormal Gaps
Large gaps in wood floors that do not close up in more humid months can be caused by job site conditions, handling and storage, or manufacturing variables. Generally, a site inspection is necessary to determine the actual cause or causes of abnormal gaping. Linda Lockwood has been trained and certified t to inspect wood floors and determine the probable cause (s) of problems such as abnormal gaping.

When the complaint is gaps between flooring pieces, the moisture content of flooring will normally be significantly lower than when the flooring was installed. The sub-floor and joists will also contain less moisture than when the flooring was installed.

A very moist job site environment will often cause wood flooring to expand before, or soon after, installation. When this happens, the strips, planks or parquet units close on one another. The flooring will move or reposition itself and, if the pressure is sufficient, cupping or buckling may result. Once the dry (or heating) season arrives, the total moisture environment changes, and the flooring and under-floor structure will dry out. If the earlier moisture absorption was great enough, the drying season will produce “abnormal” or permanent gaps. From this point the gaps will most likely never completely close in humid months.

Manufacturing related causes for Gaps:
Another cause of abnormal gaps can be improperly manufactured wood components. This usually occurs because the wood flooring is not adequately dried before the flooring is milled. For wood flooring to perform best in most areas of the country, it should be manufactured between 6-9% moisture content. When wood is manufactured; cut, sanded and/or finished above 9% it tends to loose moisture after installation, resulting in permanent gaps.

Other causes for Gaps in Strip and Plank Floors which have little relationship to job site moisture problems:

  • System Movement: When outside walls settle, or the center supports under the house’s center beam move, the area of the floor actually stretches, causing gaps over joints in plywood sub-floors. This can be detected in foundation walls or by checking the flatness of the floors.
  • Drying near forced hot air heating ducts or vents:When gaps are associated with areas above heating plants, heating supply vents (particularly closed vents) etc.
  • Improper sub-floor materials: Nail-holding capability is very important in floor installation. If the sub-floor does not hold nails well, gaps can occur from less-than-abnormal moisture absorption or heavy traffic.
  • Manufacturing related gaps.

Linda Lockwood is one of very few inspectors properly trained and qualified to determine the cause of gaps, and more importantly, whether they are normal (seasonal) or abnormal (permanent).

More to come….,
Linda Lockwood
Statewide Floor Covering Inspection Service

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