The National Wood Flooring Association (NWFA) has made recent revisions and additions to its now 180-page Wood Flooring Installation Guidelines manual, which highlights everything installers need to know regarding the proper installation of hardwood floors including solid, engineered, parquet, end grain, and reclaimed. From job site conditions and acclimation to substrates and underlayments, the manual takes an even deeper dive into the most up-to-date installation methods. 

NWFA’s Brett Miller, vice president of technical standards training and certification, was on hand to answer installers’ questions regarding some of these most recent hardwood installation methods and best practices. 

Q: Can you please go deeper into the 5" guidelines installation? In other words, glue-assist nail down.

Miller: This was pulled through a lot of collaboration in the industry to determine what should we require or what should we suggest? Being a guideline, all we can really do is make a suggestion. What we’ve stated is, anything greater than 5" should be, when possible, nailed down and assisted with glue if it’s going to be nailed. The reasoning is, if you’re nailing down a strip floor—2¼", 3", 4" floor—and you jump up to above 5", the amount of fasteners per square on that floor are diminished often times in half if not greater, and today, more floors are getting installed that are wider and wider plank and we are relying on a fastener per square foot. An adhesive addition helps.

The reason 5" is a key number is to coincide with NOFMA [National Oak Flooring Manufacturer’s Association] grading. NOFMA defines strip flooring as anything less than 3", plank flooring as anything that’s 3" up to 5" and anything greater than 5" is considered wide plank flooring. There’s a differentiator between installation methods of each one of these widths of plank.

Q: What glue methods for solid flooring—side fastening, full spread or skip gluing and adhesive types are NWFA-approved?

Miller: The only real answer to that is the type of adhesive that should be used needs to be an elastomeric wood flooring adhesive. Some guys will go to a big box store and buy some standard construction adhesive that dries very brittle and doesn’t remain elastic. If that floor or subfloor goes through any sort of movement, that bond will be broken and that becomes a pivot point on that floor which can create noises and squeaks and all kinds of issues. 

As for the pattern that you use, the only time we would suggest using full spread over a wood subfloor is if conditions below that subfloor are controlled and conditioned. If you’re going over an unconditioned space, say an unconditioned crawl space or an unfinished basement, it’s normally not recommended to go full spread because of the potential of the permeability of that adhesive negatively effecting how much moisture spreads.

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