Snaps, crackles, and pops including squeaks and creaks can be issues resulting in callbacks for wood flooring. First, what should the customer expectation be for noises and wood flooring? The occasional noise can be acceptable. Noises all over and multiple repeatable noises generally are not. A repeatable creak can often be quieted with a fastener into the area of the noise. The source of a non-repeatable noise can be difficult to determine. Eliminating it often will require more than just an additional fastener.
Noises in solid wood flooring can be associated with any element in the flooring system:
• The flooring itself.
• The fastener connection between flooring and subflooring.
• The subflooring connection to the substrate or wood joists.
The Flooring
A loose match, the tongue and groove fit along the edge of boards, allows movement between flooring boards. A loose end match will not generally contribute to noises unless other parts of the system are not adequate. Creaks occur as the boards rub against one another when walked on. If the bottom lip of the groove is too thick or thin additional movement can occur between boards. Products manufactured by NOFMA members are certified to be properly manufactured to an acceptable standard for tongue and groove match and NOFMA provides recourse if problems do arise.
Fasteners
The fastener connection is the most common cause of noises in flooring. Too few fasteners, fastening technique, improper fastener, and sometimes too many fasteners can lead to noisy floors.
Too few fasteners as a reason is perhaps obvious. If the flooring is not fastened it will move, creak and squeak when walked on. The NOFMA recommended fastening schedule for solid 3/4-inch-thick strip flooring is every 10 to 12 inches with at least 2 fasteners in every board within 1-3 inches of the ends. For plank flooring the interval should be every 8 inches. The occasional extra face nail is also acceptable for plank floors where extra movement is detected.
Fastener technique, how the flooring is nailed, is next. Actions that contribute to broken and split tongues are often associated with the crackle and squeak. A technique that uses the action of nailing alone to pull boards together can bend fasteners backwards. The bending action stresses the wood and results in splits along the tongue at the fastener.
Another culprit is the very popular pneumatic nailer/stapler. Using the air nailer to pull boards up is common and can easily result in tongue splits. Improper air pressure to the machine is also a common contributor that can split tongues. Too much air pressure can drive the head of the fastener deep into the flooring, causing the fastener to act as a chisel or wedge splitting the tongue. Frequently, a too-small air hose that does not supply enough air volume to the tool is used. As the tool is worked the air pressure decreases and the fastener is not set, so the pressure is increased to compensate. This can be OK only if the tool is worked continuously without pause. Every time the nailer pauses, the air pressure increases causing the next 5, 6, or 7 nails to be over driven and split the tongue. How many times a day is the nailer paused to move or properly position a board? Also, the higher air pressure prematurely compresses the limiting bumpers in the tool. If not changed, overdriven fasteners and splits become the norm. Other factors that affect tool adjustment are wood species- hard or soft, subflooring thickness, and subflooring type- plywood/OSB.
Cleats or staples? Which works better at holding the flooring and reducing noises? Both cleats and staples are accepted fasteners, but experience shows the stapling operation requires a finer adjustment and more diligent attention to the tool operation to prevent splitting at the tongue. Staples fall victim to the over driving condition more often than cleats. The wire can be driven easier into the wood requiring a finer pressure adjustment. Also, the driving blade and crown of the staple when improperly set has a grater bearing on the wood and acts as a bigger chisel than the cleat so that splits occur more often. Cleats can fall victim to the same conditions, but the smaller bearing area does not result in as many splits. The use of too many fasteners can also fracture tongues. The staple is more at risk than the single leg cleat, so watch using too many staples, say every 3 to 4 inches. In this case more is not necessarily better.
An incorrect fastener can also be associated with noises. Using a brad tacker to face-nail or nail in tight places with 3/4-inch boards is not recommended. The thin, smooth stick nail does not hold adequately. Deformed shank fasteners hold much better than smooth fasteners like finish or stick nails. For face nailing, the small square drive trim screw holds best; also 6d, 7d, or 8d galvanized casing nails hold very well. With face nailing, nail position is also important. Joists should be located and nailed into; also, face nail at board ends. When blind nailing, the consumer can’t see the fasteners to check for proper nailing. If noises occur and the nailing is determined to be less than recommended you are automatically at risk whether it is the nailing or not. You only get one opportunity to place the fastener so do it right the first time.
The Subfloor Connection
Another source of noise is the connection of the subfloor or the under floor system itself. With wood joist construction, wider spacing of joists coupled with longer spans and minimum thickness subflooring allows for system flex, movement, and noise.
The system flex and movement can also increase the incidence of noises associated with the other flooring connections. Wood flooring is not generally associated with the “code house”, minimum construction materials at maximum spacing; but when it is, the performance can be expected to suffer and result in noisy floors. With slab construction less than minimum recommended subflooring can result in improper fastener holding. The minimum is 3/4-inch plywood, not OSB or 5/8-inch plywood. Other factors affecting flooring over slabs include flatness of the slab and the fastening of the plywood or sleeper to the slab. If the slab is not flat to recommended tolerance (1/4-inch in 10 feet or 3/16-inch in 6 feet) the space between the subflooring and slab can cause objectionable noises or hollow sounds. If the fastening technique, such as shots, screws, pins or nails, does not hold the subflooring tight enough, then movement can result in noise.
Finally, there are some other special situations that can result in noisy floors. Transition areas are generally high traffic areas, and the connections at the transitions must be correct. Where flooring reversals occur, the slip tongue or spline must be inserted into the groove and blind nailed into place. Face nailing the two adjoining groove edges is asking for trouble from movement and noises. If the flooring is turned 90 degrees at a transition or into a separate room, a tongue and groove engagement must be provided by either the factory end match fitting the side match or re-grooving and inserting a spline.
Old floors are especially prone to noises. When repairing an old floor, setting realistic customer expectations is a primary concern. Most of the time we must inform the customer that noises can be reduced but not eliminated. A totally quiet floor is not a proper expectation. Moisture conditions can be another cause of noises. Too much moisture and expansion can stress any connection and loosen fasteners. Too little and associated shrinkage can create a loose fit and the squeaks and creaks result. One of the functions of #15 felt is to minimize this normal winter condition and reduce movement and associated noises.
In order to fix the noises the connection causing the noise should be determined. Where an area of the floor system flexes and noise is produced, the under floor system is generally the source. Fastening the subflooring from below or strengthening the system with support may quiet the noises. If the individual board moves and creaks, the flooring itself or the fastening is suspect. Fastening through the face or screwing from below is a repair option. Remember, a repair should not be noticeable from a standing position. The occasional noise in the floor can generally be fixed by proper fastening at the area associated with the noise. For a generally noisy floor, extensive face nailing or extensive screwing from below, if possible, are repair options; but may not sufficiently quiet the flooring. The next option is to replace and reinstall. If the fastening is inadequate or the site environmental conditions were not correct at installation, then the contractor is significantly at risk for the replacement even if not totally responsible. Again, do it right the first time so you won’t have to do it again.

Thanks again to JJhaines for tech info.