When we get to the stage of a home where it is time to put down the subfloor, I inevitably get the same question, “Shouldn’t you screw the floor down to prevent squeaks?” This misconception is so rampant in the building world that I felt the need to spread the word about what really happens. Here is the background:
Back in the old days (pre-1970s) subfloors were nailed down directly to floor joists. This wood-to-wood connection offered ample opportunity for squeaks, and screwing down the floor probably did help to some degree. However, over the past several decades, subfloors have been glued down to the floor joists. Glue provides a “cushion” between the wood surfaces and knockes out a bunch of these wood-to-wood squeaks. This does not solve the problem entirely, however, due to a phenomenon that occurs a bit lower in the system. The over whelming majority of homes (Close to 95% percent of homes in Kansas City) still use the old-fashioned method of stick-framing with 2x10s as the floor joists. These 2x10s, called dimensional lumber, and are supposed to be 1 1/2 ” x 9 1/4″ in size. In reality, 2x10s can be anywhere from 9 1/8” to 9 3/8” (or worse!) when they come out of the mill. To most people a ¼ inch difference may not sound like much, but when framing a floor this causes big problems when they are laid next to each other (usually 16” apart). Imagine two 9 3/8” joists with a 9 1/8” joist in between when the subfloor is glued and nailed to the top of it, the middle joist will want to “raise up” ¼” off its support (typically a steel beam with a wood plate on top of it) because the subfloor wants to hold its shape. Now, if the joist was not nailed to the beam plate, the floor would feel a little “spongy” but there would not be a squeak. The squeaky culprit turns out to be the innocuous looking “toe nail” that is driven in at a 45-degree angle to hold the joist to the beam plate. The joist sits up normally due to the subfloor but then gets pushed down when you step on that area. The action of the 2×10 sliding down on the toe nails is what generates the sound. Those little buggers can make it sound like the whole house is falling apart when you step down…and it’s all from a single little nail! Since most homes are built this way (even brand new homes), invariably, most if not all have or will have squeaks.
The good news is if you can access the beam at the squeak location (like in an unfinished basement) a simple shim under the joist will eliminate the sound. The bad news is if you cannot access the beam location (like in the 2nd floor or if you basement is finished) the job just got a lot harder (and messier). Note, you could put 10,000 screws in this floor and it would not make a bit of difference (other than waste a lot of time and money). The best thing to do is skip the 2x10s all together and use either a TGI (silent floor) system or even better, Open Web Trusses.