by Brett Miller
Wide plank wood flooring accounts for the majority of all new wood floors being installed today. According to a 2016 US FLOOReport, solid plank flooring accounted for 55 percent of the total flooring sold. Many would argue that this number should be even higher when you include engineered flooring sales, which account for 57 percent of total square-feet sales in 2017, the majority of which are wide plank products.
Today’s wood flooring manufacturers are staying in front of this timeless trend by continuing to offer wider widths and longer lengths. Standard widths being sold today have grown to 5”, and some producers are even moving up to 18” widths in boards that are up to 12’ long. Some of the oldest solid floors in many of the historic homes across the country contain board widths upward of 24”. These historical treasures have been in place for hundreds of years and are being discovered and restored on a daily basis.
Plank flooring is defined as solid or engineered boards that are 3” and wider. NWFA Guidelines for installation of plank wood floors were last updated in 2012 and are currently in the process of being completely overhauled. This overhaul includes the long-overdue updates to the plank flooring installation methods. This article will focus on some of the standard installation methods to follow when installing plank flooring. The second part of this article will get deeper into many of the common methods used to install plank flooring that may not be addressed in the current NWFA Guidelines.
There are many nuances when installing wide plank flooring that must be taken into account to ensure a successful installation. As with any installation, an essential first step is to conduct a detailed pre-installation site survey. Guidelines that pertain to all wood flooring installations can be found in the NWFA Installation Checklist available at nwfa.org.
Solid wide plank wood flooring installation methods can vary from one manufacturer to the next, but how it reacts to a gain or loss in moisture is universal. The extent to which a solid plank wood floor changes dimension (shrinks or swells) when it loses or gains moisture is directly proportional to its width. Engineered wood flooring installation methods also vary from one manufacturer to the next. It is always important to follow the manufacturer’s installation instructions with any product in order to ensure their product is being put to use as it was intended. The manufacturer normally indicates which installation methods are appropriate for the flooring being installed, which may include which type of moisture tests are required, which type or brand of adhesives to use, which underlayments, which fasteners (length, gauge, and frequency), and any other requirements specific to the product itself.
There are many required processes to take into account before installing a plank floor. If and when the manufacturer states, “follow NWFA Guidelines for installing solid plank wood floors,” proceed as the NWFA Guidelines suggest. In short, these are general guidelines:
SOLID PLANK INSTALLATION
Solid plank wood floors can be installed successfully above-grade or on-grade, but are not recommended for installation below-grade.
Solid plank flooring should be installed perpendicular to the joists, or on a diagonal for any single layer subfloor. (See NWFA Installation Guidelines for exceptions to this rule.)
Ensure the environmental conditions of the space and the moisture content of the substrate coincide with the moisture content of the flooring (and when applicable, the manufacturer’s requirements). In general, there should be no more than 2 percent difference in moisture content between properly acclimated wood flooring and wood subflooring materials.
As a general rule, a 3/4” expansion space should be left around the perimeter and at all vertical obstructions. Since solid wood doesn’t shrink/swell notably in its length, 3/4” may be overkill on butt-end walls. To minimize expansion on floors wider than 20’, or depending on geographical area, interior climate control, and time of the year, expansion may need to be built into the floor itself (washer rows). Undercutting vertical obstructions may assist in gaining the required expansion space.
For glue-down solid plank flooring over concrete:
Engineered plank wood floors can be installed successfully on, above, or below grade level.
Engineered plank flooring should be installed perpendicular to the joists, or on a diagonal for any single layer subfloor. (See NWFA Installation Guidelines for exceptions to this rule.)
Ensure the environmental conditions (temperature and humidity) of the space and the moisture content of the substrate coincide with the manufacturer’s requirements for the flooring going in. Check the moisture content of the substrate to ensure it is aligned with the ambient conditions (at EMC).
As a general rule, the engineered flooring material thickness dictates the expansion space left around the perimeter and at all vertical obstructions. Engineered flooring can shrink/swell both in width and length, so expansion is critical in all directions. To minimize expansion on floors wider than 20’, use of t-molding or other transition pieces recommended by the flooring manufacturer may be necessary, depending on geographical area, interior climate control, and time of the year. Undercutting vertical obstructions may assist in gaining the required expansion space.
For glue-down engineered plank over concrete:
In general, try to stagger as much as possible with minimal or no H joints and no stair-stepping patterns with plank floors. Attempt to stagger end-joints of boards row to row a minimum of twice the width of the flooring. For example, 8” minimum stagger for 4” planks, 12” stagger for 6” planks. Although this is ideal, many wide plank flooring products will not allow for such a wide stagger due to the amount of shorter boards.
Some common installation methods not addressed in the current Installation Guidelines include use of adhesive over wood subfloors, whether as a glue-assist application or full spread application:
Brett Miller is VP of Education & Certification at the National Wood Flooring Association in St. Louis. He can be reached at firstname.lastname@example.org.