You can fasten your plywood underlayment using one of the following: galvanized, coated chisel-point staples with a 1/4" maximum crown; galvanized, coated ring shank underlayment nails with a 3/16" diameter head; or flathead wood screws treated with a moisture-resistant coating (such as galvanized or zinc).
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.
Yes, gluing plywood to a subfloor can add strength and reduce the chances of squeaking. Use a construction adhesive like Liquid Nails and apply it in a zigzag pattern before screwing the plywood down. This helps to bond the layers more securely, especially in high-traffic areas.
You have the top layer that is your floor covering (Hardwood, Laminate, Vinyl, Carpet, etc.), next you have the underlayment (usually a thin layer of fiber, foam, rubber), below that you have your subfloor (plywood, OSB, concrete), and lastly you have the joists which are the foundation to your floors.
You can fasten your plywood underlayment using one of the following: galvanized, coated chisel-point staples with a 1/4" maximum crown; galvanized, coated ring shank underlayment nails with a 3/16" diameter head; or flathead wood screws treated with a moisture-resistant coating (such as galvanized or zinc).
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.
If you are looking for a subfloor adhesive with a powerful, permanent bond, try Loctite PL 400 VOC Subfloor & Deck Adhesive. It sets quickly and is ideal for heavy-duty interior or exterior subfloor installation in all types of environmental conditions. That means it even bonds wet and frozen lumber!
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.
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%.
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.
Use 1-1/4-inch screws for basic tasks where strength is less of an issue or when attaching two 3/4-inch-thick boards across the grain. Keep some 2-1/2-inch deck screws for screwing into end grain, plus some stronger 3-inch screws for attaching into end-grained boards or when you need a little extra power.
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.
Improperly spaced and placed subfloor panels can cause performance issues and lead to various structural failures, such as raised joints or buckling. While installing panels too tightly or without any gaps won't allow the material to expand and contract, leaving too much gap can cause excessive movement and noises.
OSB weighs more than plywood. OSB doesn't hold screws, nails, and fasteners as firmly as plywood. OSB swells more than plywood when it comes in contact with moisture, and it generally remains swollen to some degree. While both OSB and plywood off-gases formaldehyde, OSB off-gasses more of the harmful gas than plywood.
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.
Wall studs are nailed vertically to the bottom wall plate, and the wall plate itself is nailed (downward) into the subfloor, with nails even extending into the joist. All items except underlayment and floor covering rest under and are nailed to the bottom wall plate.
For subflooring, 3/4-inch plywood is generally the better choice compared to 5/8 plywood.
Installing Plywood Underlayment
While underlayment traditionally was glued down to wood subflooring, most manufacturers today recommend installing it without glue, which greatly simplifies the installation. Thorough fastening of the underlayment panels is key to a successful installation.
Coverage: One 24 oz. can of AdvanTech subfloor adhesive yields approximately 400 linear feet of gel adhesive as 1/2" bead compared to applying a 28 oz. cartridge adhesive at 3/8" bead yielding approximately 38 linear feet. Coverage will vary based on bead size and weather conditions.
Plywood is considered the most popular material used for subflooring, it has been used since the 1950s and remains one of the top choices for contractors. Standard plywood works perfectly fine as a subflooring material, but the best option is ¾” tongue-and-groove plywood subflooring.
No subfloor is perfectly level, but any signs of unevenness and high or low spots must be remedied. Please follow these requirements: Subfloor unevenness cannot be greater than 3/16 of an inch over a 10-foot span or 1/8 inch over a 6-foot span.
(3) Fasteners for 5-ply plywood Underlayment panels, and for panels greater than 1/2 inch thick, may be spaced 6 inches on center at edges and 12 inches on center each way intermediate.
When installing sub-flooring, you'll want the rough side facing up as well for traction when working. This is especially true when you have OSB that has been treated with a sealant or moisture barrier. Moisture resistant resins can create even more slippery surfaces.