Nearly 80 percent of homeowners agree that wood flooring in a home helps increase the value of their home over any other floor covering. One of the current trends that homeowners are clamoring for is the look of wide plank wood.
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:
- Moisture control systems are always strongly suggested.
- Use an adhesive and/or moisture control system approved by the flooring manufacturer. If none is recommended, use a system that matches the requirements of the space the flooring is going into.
- Follow the installation procedure recommended by the adhesive manufacturer, which includes subfloor moisture test methods and limits, spread rate, trowel size, open time, working time, flash time, use of rollers, and use of straps/tape as necessary.
Mechanically fastened solid plank floors:
- Where necessary add a vapor retarder over the wood subfloor.
- Nailing: Blind-nail through the tongue using 1-1/2” to 2” fasteners. Fasteners should be spaced every 6 – 8”, and 1 – 3” from each end. Some wood flooring installations may benefit from a decrease in spacing between fasteners, as long as it does not cause splitting of the tongues. Higher gauge fasteners (18 gauge) may require, and allow for a tighter fastener schedule.
ENGINEERED PLANK INSTALLATION
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:
- Moisture control systems are always strongly suggested.
- Use an adhesive approved by the flooring manufacturer.
- Follow the installation procedure recommended by the adhesive manufacturer, which includes subfloor moisture test methods and limits, spread rate, trowel size, open time, working time, flash time, use of rollers, and use of tensioners/tape as necessary.
Mechanically fastened engineered plank floors:
- Where necessary, add a vapor retarder over the wood subfloor.
- Use the appropriate fastener and a nail gun required by the flooring manufacturer.
- Typical fasteners used for engineered flooring are narrow crowned (under 3/8”) 1 – 1-1/2” staples or 1 – 1-1/4” hardwood flooring cleats, spaced every 3 – 4” with staples, every 4 – 6” with cleats, and within 1 – 2” of end joints. Some wood flooring installations may benefit from a decrease in spacing between fasteners, as long as it does not cause splitting of the tongues.
Floating engineered plank:
- Subfloor flatness and perimeter expansion are critical to the success of a floating floor.
- Install a vapor retarder or resilient pad underlayment as directed by the flooring manufacturer.
- Floating plank engineered flooring is normally edge-glued or edge-attached with a self-locking mechanism. (For edge-glued products, use an adhesive approved by the flooring manufacturer.)
- Perimeter expansion space at all vertical obstructions is critical. A floated wood floor becomes one monolithic unit and should not be bound at any point. It is also necessary to use t-molding or other transition pieces throughout a floated floor installation.
As a general rule of thumb when racking plank flooring follow these guidelines:
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:
- Glue-assist, or using adhesive in conjunction with using fasteners, is a common installation method in many markets over wood subfloors. Things to note when using this installation method:
- This installation method doesn’t require the use of a traditional vapor retarder over the subfloor, which enables the glue to stick to the wood subfloor rather than the paper.
- In order to alleviate the vapor retarder, it is necessary that any moisture from within or below the subfloor is at the same level as above the floor space before, during, and is maintained post-installation.
- Another option when the conditions below the substrate cannot be controlled is to use a liquid-vapor retarding membrane compatible with the adhesive and the subfloor. The perm rating of the membrane should be greater than 0.7 and less than or equal to 10 per NWFA Guidelines.
- The nailing schedule should remain the same as normal installation for the plank flooring being installed.
- Full spread direct glue installations over wood subflooring may be appropriate in some situations. The critical factors to take into account include compatibility of the adhesive and the subfloor, and the identification of any moisture-related issues below the subfloor (crawlspace or basement). If the relative humidity below the subfloor is elevated, the space is unconditioned, or moisture in any form is present, full spread adhesive application or use of any type of flooring moisture control system with a perm rating less than 0.7 should not be used. The reasoning is simple:
- A fundamental principle in nature is for materials in vapor form to seek equilibrium. Materials that are higher in concentration in one area will disperse to areas of lower concentration. This process is called vapor diffusion. Cooler air in unconditioned crawlspaces and unfinished basements inherently has higher relative humidity levels and will naturally find its way upward, through the subfloor and wood floor, into the warmer, drier air within the living space. An intact vapor retarder is designed to slow this moisture migration, but not stop it.
- When covering the wood subfloor with a moisture control system that blocks this moisture such as an impermeable membrane, the potential for this moisture to become trapped in the subfloor becomes greater. According to the Environmental Protection Agency, these types of vapor barriers can prevent damp or wet building materials from drying quickly enough to prevent mold and fungal growth…potentially leading to rot.
- Wood subfloors can rot when exposed to long-term moisture. This is caused by a wood-destroying fungi that attack and eventually disintegrates the wood fibers within the subfloor material.
There are many installation practices that professionals in our industry use every day. The NWFA Installation Guidelines were developed by our industry to ensure successful installations with all types of wood floors. Because wide plank flooring has become the most common product sold and installed today, the evolution of our guidelines will continue to explore the many methods used to install them. We also must ensure the installed flooring we put in today will last hundreds of years to come so that the future generations can discover and restore the buried treasures we leave behind.
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.