NOFMA Tip Sheet

Where the flooring crosses rooms away from walls, screw a backer block of flooring so the starting run tongue edge is also exactly under the string line.


Later, as five or more runs are nailed away from the starter, the backer will be removed and a slip tongue or spline glued into the exposed groove to create a tongue for blind nailing the reversing edge.
Nail-down or mechanically fastened installations of solid wood flooring fall into two basic divisions; thinner materials, 1/2-inch and thinner, and thicker materials, 3/4-inch and thicker. Another classification is the mechanically fastened engineered product. It goes without saying, but I’ll say it anyway; the site must be ready for the flooring installation. A near occupied environment must be established: all windows and doors permanently installed, properly caulked and weather stripped; all wet trades completed, tile and other stone work; wall an ceiling texturing completed and walls primed. The moisture content of interior wood materials and the subflooring must be within 4 percent of the average moisture content found in most homes of the surrounding geographical area. Always follow manufacturer’s recommendations; they prevail over any other directives. The following will apply to the thicker, 3/4-inch and 33/32-inch, solid tongue and groove wood flooring materials.

Those ends too close together, less than 6 inches between runs, "H" joints; marred ends, unusually colored boards, offset ends, etc. can be removed and or repositioned.
The first step for mechanically fastened flooring is to provide a proper subfloor. Recommended materials for wood joist systems- performance rated (that is having a stamp by a panel rating association) 5/8-inch and thicker plywood sheathing or 3/4-inch OSB (oriented strand board). The subfloor must be: properly fastened with ring shanked nails or screws; clean, swept and scraped of debris; dry, within the correct range of moisture, 4 percent of the area average; and flat, edge seams of panels sanded flat if necessary, and the gradual overall deflection or deviation within 1/4-inch in 10 feet or 3/16-inch in 6 feet.

Next establish the direction and layout of the flooring. The flooring should be installed perpendicularly or across the joists. Pick an area to start the installation; this is the longest area the flooring will run continuously end to end. This is typically along a center wall, down a hallway, or along the great room wall. Roll out #15 felt along this run and pull a string line along this starting line. The line should be the width of the flooring plus 3/4-inch from any associated wall line. Now measure into the other spaces and rooms for position with other walls and squareness with any changes of direction. The starting line may be adjusted to allow for the problem room that is not square, or the focal point that requires symmetry. For any major issue with out of square situations, review with the customer. Mark all joists intersections on wall lines and the felt paper across rooms or cased openings.

Be aware of how pneumatically driven staples seat; if overdriven, they fracture the tongue and result in movement of flooring boards and noisy floors.
For slab construction, the slab must be clean, dry and flat with a proper vapor retarder (see Nov/Dec ’02 issue of FCI). Subflooring should be minimum 3/4-inch CD ext. plywood sheathing laid on a diagonal to the flooring direction. 16-inch-by-8-foot plywood planks scored 3/8-inch across the back every 12 inches can also be an appropriate subfloor. Two layers of 1/2-inch plywood pinned together with the first layer square to the room space and second layer on a diagonal to first is a “high end” type system. Check NOFMA web-site: www.nofma.org for installation particulars. All other directives are the same as with wood joist systems except for fastener length. For face nailing, the fasteners should be cut to just less than 1 1/2inches long; small bolt cutters do the cutting easily. For field nailing, 1 1/2-inch long fasteners won’t penetrate the 3/4-inch plywood and compromise the vapor retarder. Longer fasteners can be used, but angle the flooring nailer more using a shim on the foot plate to avoid punching through the plywood.

Select the longest and straightest strips of properly acclimated flooring (see Sept./Oct. issue of FCI, regarding acclimation) for the starting runs. Also select similar boards and place to the side for the finishing runs. Position the very edge of the tongue edge directly under the string line and at all wall lines, then face nail the flooring about 3/4-inch from the groove edge at all joist intersections. Also, similarly face nail at the ends. Where the flooring crosses rooms away from walls, screw a backer block of flooring so the starting run tongue edge is also exactly under the string line. Engage the starter on the backer and blind nail (secret nail or angle nail) the tongue at joists and between joists. Later as five or more runs are nailed away from the starter, the backer will be removed and a slip tongue or spline glued into the exposed groove to create a tongue for blind nailing the reversing edge. No exposed face nails will appear across the reversing run.

After the starting runs are in place, finish rolling out the felt and begin to rack the flooring. Racking refers to flooring boards being placed on the floor and engaged without nailing. The end boards can be cut and an entire room can many times be racked. This is the time for the contractor to review the flooring for proper distribution and potential problem boards. Those ends too close together, less than 6 inches between runs; “H” joints; marred ends; unusually colored boards; offset ends; etc, can be removed and or repositioned. The problem board always gets placed in the doorway or in front of the hearth; this is the time to avoid that call back.

Fastening is next. Fasteners can be cleats 1 1/2 inches to 2 inches long, 15 gage staples 1/2-inch crown. These are driven by an appropriate flooring machine that is either pneumatically operated or mechanically driven. In addition, 6d - 7d galvanized casing or flooring nails or square head drive trim screws can also be used for face nailing at wall lines and nailing where a flooring tool cannot fit. An entire floor can be hand nailed with these fasteners, but this is seldom done. Fastener spacing is generally 10 inches to 12 inches along strip flooring, 8 inches with plank flooring. In addition, a fastener should be placed within 1 – 3 inches of each end of the boards no matter how short. Where the 1 1/2-inch fasteners are used closer spacing, 6 inches to 8 inches, is recommended. Some cautions about fastening; be aware of how pneumatically driven staples seat; if over driven, they fracture the tongue and result in movement of flooring boards and noisy floors; cleats can also cause fractures, but are not as likely. Do not rely on additional fasteners to pull a crooked board into place; the back bending of the fastener will also fracture tongues. Do not mix fasteners in the flooring field. Do not generally fasten flooring with a trim nailer; face nailing is acceptable along the starting run at wall lines and within 6 1/2 inches of the finishing wall.

Special applications. For reverses and changes of directions, perpendicular or angles, a tongue and groove engagement should be provided. Where flooring will be parallel to joist direction, solid blocking between joists every 24-inch maximum spacing should be provided or overlay with a minimum 1/2-inch thick plywood sheathing. Where flooring is placed between already in place borders, decorative features, or other flooring, work from both ends to the middle providing a tongue and groove engagement at the features and groove the cut end of fitting piece and spline for proper engagement.

Again, a clean, flat, dry subfloor is necessary; the space should be ready for flooring; the flooring acclimated as necessary; lay out is critical to the look; install perpendicular to joists; and you only get one chance to nail correctly, so do it right the first time.