Rather than nails, screws are best to use for subfloors — these fasteners are convenient, easy to remove and capable of providing torque that nails lack. Because of their structure, screws can penetrate plywood more easily and improve the connection, whereas nails can weaken the plywood.
Nails are your best bet for subfloor because a pnuematic nailer can move hardware faster and cheaper than screws. Also, nails allow for more seasonal movement than screws.
You would want to strive for 100% contact (backerboard to plywood) using thinset. Galvanized roofing nails may work best in this case. Because of the thinset you would also want to use galvanized screws to instal the plywood.
If you would like to permanently keep the flooring, nailing should be better due to the fact that it is much stronger than screwing. However, screwing should be very helpful if you are planning on removing the flooring.
The answer is: It Depends. In many applications where force is placed vertically along the installation, a screw is a better choice, but in situations where the force is placed adjacent to the installation a nail is a better choice.
When installing a 3/4″ plywood subfloor, using the correct nail size is crucial for stability and preventing floor movement. The recommended size is 8d or 10d nails, which are 2-1/2″ to 3″ long (64 mm to 76 mm).
Subfloor. Screw spacing should be 6" o.c. at the boundaries and 12" o.c. in the field, assuming an unblocked diaphragm. For blocked diaphragms increase the numbers of screws by 15%.
Don't beat the sheets together tightly, you must leave 1/8” gap at all sides of the panels to allow for swelling. The sledge makes it easy to “persuade” the sheets together, but don't hit it hard. Be very particular about that 1/8” gap.
For added strength and stability, a double-layer subfloor is often recommended. In this configuration, two layers of plywood are installed, with the top layer offset from the seams of the bottom layer. By staggering the seams, the subfloor's overall strength is enhanced, reducing the risk of deflection or squeaks.
The underlayment sheets usually run in the same direction as the plywood subflooring, but it is critical that the seams of the underlayment are offset from those in the subflooring, so the underlayment bridges over the subfloor joints.
Improper Fastener Placement in Subfloor Panels
Fasten panels using 8d ring-shank nails or other code-approved fasteners. Install fasteners beginning 3/8 inch from panel corner and then 6 inches on-center along the panel edges, and at 12 inches on-center along center supports.
PAMFast AutoFeed Screws are the preferred choice for interior and exterior subfloor. They provide a firm grip between connecting lumber, which makes them perfect for subfloor. They have a head that works with a variety of bits, including Phillips and torque-head screws.
The sheets of ply have a habit of separating when screws are inserted or even large nails. However, if you get the ball rolling with a little bit of pre-drilling this issue disappears completely. Speaking of drilling, if you're needing to drill through the faces of your sheets it's best to start on the front face.
Generally, nails (6d ring or screw shank, or 8d common) should be spaced 6 inches on center along supported panel edges and 12 inches on center on the panels' interior supports, or as specified on the construction drawings. Many manufacturers print a fastener template directly on the panel face.
Rather than nails, screws are best to use for subfloors — these fasteners are convenient, easy to remove and capable of providing torque that nails lack. Because of their structure, screws can penetrate plywood more easily and improve the connection, whereas nails can weaken the plywood.
A successful tile installation project requires a level surface. Check for dips in the floor by sliding a 4-foot to 6-foot straight edge in different directions all around the room. Mark any uneven spots you find so that you can make them level. Fill seams in the subfloor with caulk.
The minimum thickness of plywood for subflooring is about 5/8 inch. Since it does not hold fasteners as well as plywood, OSB must be a little thicker, or at least 23/32 inch.
Determining the Ideal Screw Length in Woodworking
For most woodworking projects, the rule of thumb is that your screw should be at least twice the thickness of the thinnest piece being joined. For example, if you're fastening a 1/2‑inch thick board, you would ideally use a 1‑inch long screw.
Use 1-1/2" long cleat nails when installing thinner 1/2" thick wood flooring. Use 1-3/4" long cleat nails when installing 3/4" solid wood flooring, when 3/4" thick plywood is applied directly over a concrete slab—so the cleat nail does not go through the 3/4" thick plywood, hitting the concrete.
Install the subflooring panels
Place screws approximately every 6-8" along the edges and every 12" in the field of the panel. Repeat the process with the remaining panels, making sure to stagger the joints for added strength.
1/2-inch Plywood or OSB: Use 8d common nails or 8d ring-shank nails. These nails are typically around 2 1/2 inches long. 5/8-inch Plywood or OSB: Use 10d common nails or 10d ring-shank nails. These nails are typically around 3 inches long.
Flooring joist spacing affects subfloor plywood thickness. Closer joists (16 inches apart) can use thinner subfloors (1/2 inch), but wider spacing in older homes may require thicker materials (7/8 inch plywood or 1 inch OSB). Proper thickness of subfloor ensures floor stability and comfort.
For traditional plywood flooring installations, where the plywood is directly attached to the subfloor, the recommended plywood flooring thickness typically ranges from 5/8-inch (15mm) to 3/4-inch (19mm). While 3/4-inch plywood is standard for most residential subfloors, certain conditions may require thicker plywood.