Question 1

How many sheets of plywood do I need?

Accepted Answer

Divide the area by 32 square feet per 4 × 8 sheet and add 10% for cuts. A 24 × 16 ft floor is 384 ft², so 384 ÷ 32 = 12 sheets, or 14 with waste.

Question 2

How many square feet in a sheet of plywood?

Accepted Answer

Thirty-two, for a standard 4 × 8 sheet. A 4 × 10 sheet is 40 ft² and a 4 × 12 is 48, though both are less commonly stocked.

Question 3

What thickness plywood for a subfloor?

Accepted Answer

Three-quarter inch tongue-and-groove over joists at 16 inches on centre, and thicker or an added layer at 24-inch spacing. Under tile you generally want 3/4 inch plus an underlayment, because deflection cracks tile long before it troubles the plywood.

Question 4

Plywood or OSB for sheathing?

Accepted Answer

Structurally comparable at the same rating, and OSB is cheaper. Plywood handles repeated wetting better and dries faster, which matters on a roof deck or anywhere that may sit exposed. OSB swells irreversibly at cut edges once soaked.

Question 5

Which way should plywood run?

Accepted Answer

With the face grain, or the strength axis on OSB, perpendicular to the joists or studs. That is how the panel is designed to span. Running it parallel roughly halves the span rating and is a common cause of a bouncy floor.

Question 6

Do I need a gap between plywood sheets?

Accepted Answer

Yes — an eighth of an inch at all edges. Panels expand with moisture and edge-to-edge installation causes buckling. Tongue-and-groove subfloor panels have the gap designed into the joint already.

Question 7

How many nails per sheet of plywood?

Accepted Answer

About 50 for a standard pattern of 6 inches on centre at the edges and 12 in the field. Ring-shank nails or screws hold far better than smooth nails, which is why subfloor squeaks usually trace back to smooth fasteners.

Question 8

What does CDX plywood mean?

Accepted Answer

C-grade face, D-grade back, exterior glue. It is a sheathing panel, not a finish one — the X refers to the adhesive rather than making it suitable for permanent exposure. For visible work, use a BC or better face grade.

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