How to Build a Squeak-Free Floor

Here are my ideas for using the right joists, sheathing, adhesive, and fasteners to prevent squeaky floors.

Use Engineered Wood Joists
It may cost a little more but I always recommend that you use some type of engineered floor joist system. Dimensional lumber works fine, but unless you buy an expensive grade of lumber that is kiln dried you may be disappointed. “I-Joists” are a good alternative to dimensional lumber.

I prefer truss joists with open web members, mainly because the open webs allow the installation of mechanical, electrical and plumbing without drilling and notching. Ductwork is impossible to install in a 2x wood joist system without building furred down ceiling areas below the joist system for the larger duct runs, and I don’t like they way the ceiling looks when this happens.

One key to keeping a floor or framing system from squeaking, bouncing, or popping is to minimize deflection when you walk on it. Wood truss joists are often stiffer than dimension lumber joists. You can have a perfectly built floor system, but if it deflects too much the squeaks and pops will start coming from the nails holding the wall bottom plate framing to the floor. So, over-engineer the supporting framing a little.

Depending on the subfloor panel you choose, the floor trusses could be spaced 24 inches on center to maximize the space for ductwork. If you try to save money on decking by using a thinner panel, you will need to decrease the joist spacing. In other words, you spend less on decking but more on joists.

One drawback to floor trusses is that they may need to be tall enough to get large duct through the webbing. Taller joists mean a taller building and additional square feet of siding, for example. By planning ahead, you can get your heating contractor to change the duct dimensions to minimize the height of the joists. When you know what the routing is for the duct, the joists can also be designed with prepared openings for the duct. (Don’t forget to allow for the extra width and height if the duct must be wrapped with insulation.)

I recommend floor trusses that are 14 inches tall. After you subtract the top and bottom chord of a standard structural floor truss, you end up with only 12 inches of vertical space for big things like ducts to pass through the web spaces. A 12-inch tall truss leaves only 10 inches. If you have a girder floor truss that supports a heavy load above or supports multiple floor trusses at one end, you have even less vertical space between the webs because they often are constructed with double top and bottom chords.

Keep in mind that long span lengths of your floor trusses will deflect more (move up and down with the occupant loading). Talk to your floor truss provider about designing the trusses to minimize deflection.

Use Engineered Subfloor Sheathing
I recommend a 1-1/8” T & G Sturd-I-Floor panel for the subfloor. OSB and plywood both perform well. In some parts of the country, OSB may cost a little less than plywood.

Make every effort to keep the subfloor dry during construction. If it does get wet, don’t allow water to puddle on the surface for any length of time. Wet plywood delaminates and OSB swells.

Use the right Sturd-I-Floor panel for the center-to-center spacing of the joists. Sturd-I-Floor panels are stamped from most mills with a single number -- 16, 20, 24, 36, or 48 -- which is the maximum center-to-center spacing for the supporting joists.

Most panel products must be spaced apart at the edge to allow for expansion and contraction. Trying to be conscientious, framers often think that if it looks like the panels fit tight together it is good; however in this case it is not. Most wood panel products must be spaced, usually 1/8 inch to perform properly. Subfloor sheathing is no exception.

Use Adhesive and Install It Properly
As I have mentioned in other articles, the adhesive is often the weak link in the floor system. This is because framers think they know how to install it.

The most common mistakes are: Not using enough adhesive, and/or delaying the full fastening of the sheathing.

The adhesive will not do its job if it is allowed to skin over or dry before the panels are fastened down. Just tacking down each panel as it is installed is not good enough.

I recommend (and most adhesive manufacturers say this on the label) that no more than one or two panels be placed onto the adhesive before it is nailed completely.

Put a small bead (1/8-inch) of adhesive into the groove before you push the tongue and groove panels together. This eliminates the possibility of squeaks at the tongue and groove joint where it is unsupported between the joists.

Use an adhesive that conforms to APA Performance Specification AFG-01 or ASTM D 3498.

Make sure your framer follows the instructions on the adhesive container. Use the right size bead under the right temperature and moisture conditions.

Use the Right Fastener
A tight connection between the subfloor sheathing and the joist can be accomplished with the right type of fastener. Plain nails, even galvanized nails, do not grip the joist well enough. They eventually wiggle loose.

I recommend a screw-shank nail, or better yet a screw. Ring-shanked nails work if the wood grain is perpendicular to the nail, which is often not the case. So stick with a proven fastener type. It may cost a little more, but what price are you willing to pay for silence?

What Goes Over Your Subfloor?
If you are putting carpet and pad over the subfloor, your squeak-elimination job is done. Other flooring materials are a different story:
•Tile – use full coverage thinset tile adhesive to attach minimum ¼-inch cementitious backerboard to the subfloor. Strictly follow the product manufacturer instructions.
•Sheet vinyl or VCT – glue and screw 3/8-inch (minimum) underlayment-grade plywood. Emphasis on “underlayment-grade”. Resilient floor manufacturers recommend plywood underlayment, not particle board.
•Hardwood flooring – talk to your installer about your options for eliminating squeaks. Use subfloor sheathing with a higher span rating. For example, instead of using “Sturd-I-Floor 24 oc” use “32 oc”. Also, orient the hardwood flooring strips perpendicular with the floor framing, if possible.

Summary
On my house I would:
* Use engineered plate connected floor trusses spaced 24 inches on center, designed to minimize deflection.
* Use 1-1/8” Sturd-I-Floor 24 oc (32 oc is better yet), T & G.
* Fasten down with an approved adhesive and 2-1/2 inch screw-shanked nails 6 inches on center on the edges and 8 inches in the field.
* Glue the tongue and groove joints.
* Follow all product instructions for the trusses, sheathing and adhesive.

If your house is already built, and you screwed the floor down properly, read our article on framing squeaks associated with floors. Fixing a Squeaky Floor