By Brett Miller

How will the joist spacing affect the performance of your flooring?

Why does NWFA have more stringent recommendations than the minimum building code? What am I supposed to do?

Brett Miller, vice president of certification and education at the National Wood Flooring Association, answers:

First, let’s get the recommendations straight. For joist spans 19.2–24 inches, NWFA “Installation Guidelines” recommend a minimum panel thickness of 7⁄8-inch OSB or plywood; the minimum building code (which most builders build to) is 23⁄32-inch OSB or plywood. For joist spans 16 inches or less, NWFA recommends minimum panel thickness of 5⁄8-inch plywood or 23⁄32-inch OSB; the building code requires 5⁄8-inch plywood or OSB. When NWFA Guidelines minimums are not met, the recommendations are to overlay the existing subfloor material with a 1⁄2-inch panel product or add structural support from below. Both cost money and time and will likely exceed the traditional installation costs.

How many installers turn away the job because the builder refuses to pay for these corrections? Very few! How many flooring professionals are confident taking on the liability of adding bracing between the joists to increase the stability of the subflooring system for our wood floor? Very few!

The building code for the subfloor is to ensure structural loads are adequate—from a safety perspective, not necessarily from a wood flooring performance perspective. With much of today’s wood flooring being thinner, wider plank installed on the minimum building code panel thicknesses, we are seeing more creaks, pops and squeaks.

When these issues occur, who’s to blame? The manufacturer, distributor, builder or installer? It is not uncommon to see a properly installed floor still exhibit these issues. In the end, if the consumer is not happy, someone will be left holding the cards. The cost is either shared, or one of the involved parties takes the biggest hit, which can be extremely damaging to any business. The problem is, the builder will still build to the minimum standard, and the issue will arise again. So what should you do?

1. Check the subfloor joist span to determine whether it’s sufficient for the flooring.

2. Document your findings.

3. Put together a plan and cost to achieve what is recommended and present it to the builder/homeowner.

4. Document the conversation.

5. If they decline to compensate you for the additional work necessary, it is up to you to determine if the work is worth the potential liability.

If you have been installing floors over these subflooring systems with success, maybe you don’t need to change a thing! But that one hit can quickly turn production income into a nightmare job.

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