Most people think that every hardwood floor gets secured to the subfloor the same way. This is not true. Depending on the type of subfloor you have, and the type of hardwood you select, the methods differ greatly. The biggest factor in determining the type of fastening system is the type of subfloor.
If the subfloor is concrete, then glue will have to be used. Obviously, you can't shoot nails into concrete and they do not make some that you can. Also, if the subfloor is made out of particle board instead of OSB then you cannot nail the floor to that either. Particle board fractures easily, so when nails are shot through it the board can blow apart causing the nails to not stick very well. This usually results in a squeak filled floor.
Next, the type of material will also dictate how you secure it to the subfloor. If nailing, then the size of the nail is extremely important. For solid hardwood, 16 gauge nails are the standard and work well. However, most engineered floors require a smaller 18 gauge nail and if anything else is used, it will void the warranty. Most engineered material is thinner, so the bigger 16 gauge nails can fracture the tongue too much causing it to break off or weaken. When the next board is attached to it, that board will have movement as the groove side will move up and down with the broken tongue.
Further, the width of the material in question dictates if glue is necessary or not. As a rule of thumb, any material 5" wide or more glue is recommended. Wider planks have a larger service area between where the nails secure it and the groove locks into the previous row. This larger area can move up and down when stepped on. This can cause squeaking and other issues. One thing to keep in mind, is that the material and labor involved with a glue down can dramatically increase the price of the floor. Sometimes, nailing and gluing are both recommended. This can make for an extremely stable floor.
If you are in the Boise, Idaho region and aren't sure about the proper way your floor should be secured give us a call! If you think your floor might have been installed incorrectly and are in need of an expert opinion we would love to help as well!