Narrow flooring that is manufactured outside the 6% to 9% moisture standard.


Excessive gapping results from too high moisture content at manufacture.

In 1909, the founding members of the Oak Flooring Manufacturers of the United States (NOFMA’s predecessor) decided to form an organization for the purpose of “promulgating and administering industry grading rules.” Some 12 years earlier, the founders of the Maple Flooring Manufacturers Association (MFMA) had done the same thing. The men behind these bold moves realized that establishing industry standards would allow for the relatively new products they were selling to gain consumer acceptance, thereby allowing these industries to flourish. And they were right. Industry standards provide a basis upon which the consumer can form a reasonable expectation for how a product will function.

To identify NOFMA warranted flooring, the NOFMA grade will be identified as well as a mill number or logo.

In 1935 the U.S. Government Division of Trade Standards established Commercial Standard CS56-36 for oak flooring based on the Official Flooring Grading Rules of The National Oak Flooring Manufacturers Association (NOFMA). This standard with periodic revisions as suggested by NOFMA was the recognized industry standard until 1972. At that time The National Bureau of Standards of the Dept. of Commerce withdrew the current standard, 4th edition CS56-60, and recognized that the Official Flooring Grading Rules of NOFMA were regarded as the ‘national standard’ for manufacture and that the FHA directed that the installation of strip flooring should conform to NOFMA recommendations. Also, The Federal Specification for Lumber, Hardwood, classified under TYPE III – Hardwood Flooring, “shall conform to the grading rules as applicable:
  • a.) National Oak Flooring Manufacturers Association. In 2000, NOFMA changed its name to -- NOFMA: The Wood Flooring Manufacturers Association.
  • b.) Maple Flooring Manufacturers Association (MFMA).
This decree from the government effectively established NOFMA and MFMA as the keepers of the industry standards for solid wood flooring. The NOFMA standards of manufacture and installation have since remained the recognized standard of the industry for residential construction and related commercial applications. Today, NOFMA warrants that its member’s certified flooring meets the standards of manufacture. The wood species covered in the Official Grading Rules are: oak, maple, beech, birch, hickory/pecan, ash, walnut, and cherry. The grading booklet is available from NOFMA for a nominal fee + shipping and handling.

To identify MFMA certified flooring, the MFMA stamp and the mill number will be identified on the flooring.

There are three basic NOFMA standards of manufacture for unfinished solid hardwood flooring–moisture content, configuration, and grade.

NOFMA moisture content standard - flooring is manufactured at 6-9% moisture content with a 5% allowance for pieces outside that range to 12% moisture content. This standard is in place so that users of the product will know what to expect and are able to acclimate the product appropriately for the conditions in which it will be permanently installed. The 6-9% range was selected because this range is consistent with the average humidity levels in a majority of the geographic regions of the United States.

NOFMA configuration standard - 3/4” and 1/2” thick flooring is manufactured to the shape of the NOFMA standardization drawing. NOFMA supplies its members with a metal flooring Go/No-Go flooring gauge to check this configuration. There is also a standard for 3/8” thick flooring, but no member is manufacturing this product at this time. The flooring gauge measures tongue and groove match on the sides (or side match), flooring thickness and flooring width. This standard helps to ensure that the tongues fit snugly in the grooves, and each piece of flooring is consistent in face width and thickness, within certain tolerances. These standards address issues such as overwood, loose match (can cause noisy floors) and gaps caused by inconsistent widths.

NOFMA grading standard - Flooring is separated by appearance characters described in the Official Flooring Grading Rules. Flooring is considered “on grade” (meeting the grading standard) if 5% or less in feet is in the wrong (does not conform to the description for that grade). Grade primarily addresses issues that affect how a floor will look after it is installed. Included in grading standards are issues related to natural characteristics as well as manufacturing marks (sticker stain, for example) and issues such as average length and end-squareness.

The combination of these three standards is what determines the suitability of a wood flooring product to a particular end use.

The original CS56-60 publication of the commercial standard for strip oak flooring.

The MFMA is recognized as the standard setting organization for competitive sports flooring applications. Their manufacturing standards cover maple and related species, beech and birch. Their standards also include the three basic standards of manufacture -- moisture content, configuration, and grade.

MFMA Grading Rules recommends the maintenance of 6 to 9% average moisture content following manufacture. The rules also state that:
Flooring shall not be considered of specified grade unless the lumber from which MFMA-RL flooring is manufactured has been properly kiln dried.

MFMA flooring configuration standard includes 1/2”, 23/32”, and 33/32” thick flooring. This is different from the NOFMA standard 3/4” configuration. However, NOFMA recognizes these as optional thicknesses for its members that manufacture maple flooring. MFMA also has provisions that allow for finger jointed flooring assembled from standard pieces to be included under its specification umbrella. 

The MFMA installation standards illustrate and describe typical systems and the components required in the installation of sports floors. The association also has provision for finish testing and conformance to their performance standard of site-applied finish. A list of conforming finishes, grading information, performance criteria, and other information is available on their website www.maplefloor.org.

All the above relates to unfinished solid wood flooring.

With factory finished product, the roughness or texture of the finish may meet the manufacturer’s proprietary guidelines.

What about Engineered and solid factory finished flooring? What are the industry standards?

As for engineered wood flooring, the Hardwood Plywood & Veneer Association has established an ANSI standard for engineered wood flooring manufacturers. This standard addresses issues specific to the manufacture of engineered wood floors and it is recognized by NOFMA as the appropriate industry standard for these products.

Factory finished solid wood flooring products are addressed to some degree in the NOFMA Official Flooring Grading Rules. However, at this time no factory finished flooring manufacturer describes its products by the terms used by NOFMA. Instead, the majority of factory finished solid producers describe their products as conforming to their own proprietary guidelines. The wise purchaser of these products will become familiar with the manufacturer’s proprietary standards to avoid unpleasant dispute resolution later on. The fact that most producers have their own set of standards for factory finished products does not exempt those products from more generally accepted industry standards, however. With factory finished flooring the NOFMA’s standards for moisture content, configuration of tongue and groove, width consistency, and the “up to 5% allowance for out of character boards” are still applicable standards. The NOFMA standard for thickness variance (“overwood”) also applies, but many industry observers believe the NOFMA overwood standard needs revision since the current standard varies with the NOFMA grade description. Under this section the most lenient overwood standard for factory finished flooring is 0.020”. Until the industry feels further standards are necessary, the proprietary items of-appearance or grade, finish performance, allowed finish irregularities, allowed “overwood/underwood,” allowed crook and bow, and edge configuration-are all established by the individual manufacturer.

This unfinished product has numerous “bit ends” which, when coupled with other grading mistakes, is considered outside the grading standard with more than 5% “off grade” pieces.

Because of this propensity for proprietary standards, when working with factory finished flooring, you should ask for and become familiar with the specific standards from the manufacturer. As the product is installed these directives will allow you to identify acceptable and non-acceptable boards. And we all know that once a board is placed it becomes our responsibility unless the latent defect surfaces later. In addition, also ask for the proprietary finish standard particularly regarding fractures and cracks in the finish. There are currently no commonly accepted “industry standards” regarding factory-applied finishes. This has become an often asked question as to what is allowed and what is not after the flooring is installed. Some finishes will show subtle fractures along the edge related to installation that are not obvious without light reflection. This may be considered an allowed finish character by the manufacturer. Also, “How much latent checking and finish fracture related to surface checking is allowed?” is another frequently asked question that currently does not have a commonly-accepted answer.  This too can be an allowed proprietary grading character for the manufacturer. Again, prior knowledge of these issues can head off expensive repairs and replacement.

As a user of solid unfinished wood products you should expect the flooring to be manufactured to the industry standard. With products manufactured by members of the MFMA or NOFMA, you can be assured of proper manufacture. And, you have the assurance that when problems are identified by the associations’ representatives as manufacturing-related they will be settled. With factory finished products the industry standard as it relates to moisture content and configuration is established, but when issues arise about finish, the directives established by the individual manufacturer prevail.