How to Install a Nail-Down Wood Floor Correctly
June 2, 2010
Always follow the wood flooring manufacturer’s installation instructions. Quality installation is a result of planning, preparation and the use of quality tools and materials. Safety is key to the success of any job. Always wear eye protection and ear protection. Inspect the jobsite to determine if it is ready for the installation of wood flooring. Make sure the building is enclosed with all windows and doors installed. Ensure the HVAC system is operating at normal living conditions. All wet work, such as concrete, masonry, plaster, drywall and paint must be complete and dry.
The exterior must also be inspected to determine grade level. Any slab that has 4” or more of earth above it is considered below grade. (Figure 1)
All drainage from landscaping, irrigation, sloped land and downspouts must be directed away from the home. (Figure 2)
A crawlspace must be covered with 6-8 mil preferably black polyethylene sheeting or visqueen. There must be good cross ventilation from vents in the foundation, with a minimum of 1.5 SF of vents per 1,000 square feet of floor space. The minimum clearance from joist to ground is 24” or 18” from the girder or any ductwork to the ground. (Figure 3)
Solid wood flooring is recommended for installation on or above grade. Engineered flooring may be installed on, above or below grade.
Moisture testing of the subfloor and solid wood floor is critical to a successful installation.
Inspect the walls, doors, windows and plumbing, noting any evidence of water damage, moisture or leaks. Use a pin style meter and insert the probes parallel to the grain of the wood floor. Take multiple readings of the both the solid wood floor and the subfloor and record your measurements.
Proceed with the installation only when the difference between the subfloor and a solid wood floor is no more than 4 percent. Consult the manufacturer’s moisture recommendations for engineered flooring.
Relative humidity is another important source of moisture affecting wood floor. Wood flooring is dried to 6-9% moisture content because in relative humidity of 30-50% and temperature of 60-80 degrees Farenheit (the range most people find comfortable), wood moisture will stabilize or reach an equilibrium of 6-9%. A hygrometer allows you to measure the humidity at the jobsite, so you can adjust the interior climate as necessary. Many jobsites will have temperatures and humidity conditions that are significantly different than the normal living conditions. Solid wood flooring must be acclimated until its moisture content is in equilibrium with normal living conditions.
This is not a specific number of days but a point where the wood is neither gaining nor losing moisture. This table allows you to determine the EMC, equilibrium moisture content of the wood floor by noting the expected temperature and humidity of the occupied home. (Figure 4)
It is the installer’s responsibility to ensure that the climate of the jobsite is modified to bring it into normal living conditions before delivering and acclimating the flooring. Engineered flooring, because of its inherent dimensional stability, may not require acclimation. Please follow the manufacturer’s instructions regarding acclimation.
The correct subfloor ensures your wood floor can be installed without undue movement, gaps and squeaks. Solid wood flooring requires a minimum thickness of 5/8” plywood or structurally rated ¾ OSB over joists that are 16” on center. Joists with a wider span require additional support, either thicker plywood, an additional layer of plywood or blocking between the joists. When installing solid wood flooring over concrete, a minimum thickness of ¾” plywood is necessary.
Engineered wood floors typically require greater structural support than solid wood flooring over joists. Please refer to the manufacturer’s instructions for subfloor requirements regarding plywood thickness and joist spacing.
Inspect the subfloor and replace areas that are not structurally sound or show evidence of water damage. Re-nail or re-screw any loose areas.
Use a straight edge to determine flatness. Shim low spots or sand high areas to achieve flatness of 3/16” in a 6-foot radius or a quarter inch in a 10-foot radius.
Undercut all interior jambs and if necessary the doors. Have a piece of flooring so that the cuts can be made to the correct height.
Then clean, sweep and vacuum, removing all debris from the subfloor. Start at the longest, straightest wall in the room or the wall that is the most visible.
Flooring should be laid perpendicular to joists and this will usually mean the floor will run the length of the room. If the floor is to be installed in multiple adjoining rooms, your layout lines must continue into these rooms and remain parallel or perpendicular to the first room. Establishing a centerline will give you the greatest accuracy in your layout. Using trammel points to transfer your lines into the adjoining room is a fast, accurate and easy way to keep all your working lines square.
Transfer the centerline line back to your chosen starting wall, establishing a working line that is 3 to 4 flooring widths, plus the recommended expansion, off the wall. (Figure 5)
Using trammel points to transfer your lines into the adjoining room is a fast, accurate and easy way to keep all your working lines square.
Now, roll out the manufacturer’s recommended moisture retarder, beginning at the starting wall, then lap each run by 3” and staple the paper down.
Cut a small wedge at each end in the paper to reveal the chalk line on the subfloor, and snap a new line on top of the paper.
For your first and starter rows, select the longest straightest pieces of flooring; be sure to reserve some boards for the final rows.
Line your first row up by measuring from the working line to the top front edge of the board. Taper the first row if necessary to maintain the expansion space and remain square to your working line. (Figure 6)
Top nail 3/4” to 1” from the back edge of the board, starting 1 to 3” from its end and every 16” along its length. Then blind nail between each top nail. (Figure 7)
Depending on the width of your flooring you may need to install 2-4 starter rows before you can begin using a Powernailer.
Begin 2-3” off your starter rows, rack the floor by creating a set of four to six boards in descending lengths.
Fill the set with similar length groups being sure to stagger end joints by a minimum of 6-8” or for best appearance twice the width of the flooring. (Figure 8)
Avoid clustering end joints, stair steps and H joints. Be sure to mix the boards from different boxes or bundles to assure the colors will be well blended. As each row is racked out, keep the end joints tight and reverse the direction of the last board in the row.
Once all the rows are racked, knock the rows to ensure they are tight and mark the final boards so they may be cut to length.
3/4“ solid floor may be installed with a pneumatic 445, a manual 45 or 45 R nailer using a 16 gage cleat.
If the floor were a very hard species like hickory or some exotic wood, the Powernailer pneumatic 50 P or manual 50 M would be another choice. Both of these machines shoot a slightly thinner 18 gage cleat that is less likely to split the tongue.
There is a Powernail machine for every flooring thickness and construction, whether solid or engineered. Powernail offers both cleats and staples for fastening floors. Both fasteners come in a range of lengths for different applications.
Because each manufacturer provides a slightly different profile, it is essential to fit the nailing machine to the flooring. Ensure the nailer is inserting the fastener in the nail pocket or precisely at the point where the tongue makes the 90 degree angle. (Figure 9)
Beginning at the left hand wall, use the Powernail mallet to knock the boards into place.
Set the nailing machine on the board and hit the plunger with the rubber end of the mallet. Slide the machine to your right and continue nailing at the recommended nailing schedule.
If you are using a pneumatic nailer, confirm the air pressure is sufficient to properly set the fastener without driving it too deep and splitting the tongue.
When installing pre-finished flooring take particular care to protect the finish. As you approach the final wall there will no longer be room to use the nailer.
Continue the installation by drilling and hand blind nailing or by using a 15 gage finish nailer. The last one or two rows will need to be top nailed.
No wood floor is complete without the proper transitions where your new wood floor meets doors or other floor coverings.
Dispose of all debris, then sweep and vacuum your floor.