What thickness of plywood do I need for a subfloor?
For 16-inch on center joists, the minimum is 5/8" (15/32") APA-rated plywood with a 24/16 span rating; most experienced framers install 23/32" tongue-and-groove instead. For 19.2" oc joists, 23/32" is the minimum and 3/4" T&G is preferred. For 24" oc joists, 3/4" T&G is the floor and 7/8" T&G is the preferred upgrade where stone tile or heavy live loads are coming. The APA span rating stamped on the panel (24/16, 32/16, 48/24) is the authoritative spec — verify before purchase.
Is OSB better than plywood for a subfloor?
Neither is universally better. Both OSB and CDX plywood are APA-rated subfloor materials. OSB costs about 30-40% less per sheet in 2026 US retail. CDX recovers from occasional wetting; OSB swells permanently at the edges when wet for an extended period. Most production homes in dry climates use OSB for cost. CDX is the better call for kitchens, bathrooms, laundry rooms, and any room directly above an unconditioned basement or crawlspace. The decision is moisture risk versus budget.
What grade of plywood is used for subfloor?
CDX plywood with an Exposure 1 stamp is the standard subfloor grade. CDX means C-grade face, D-grade back, exterior-grade glue. The Exposure 1 stamp means the panel handles temporary moisture during construction. Look also for an APA span rating (e.g., 24/16 or 32/16) printed on the panel. Anything stamped Interior or with no APA span rating is the wrong product for a subfloor. Tongue-and-groove edge profile is the preferred upgrade.
Do I need underlayment over plywood subfloor?
Usually no. Modern 23/32" or 3/4" CDX or OSB subfloor is smooth enough that most finish flooring installs directly over it. Add a separate 1/4" plywood underlayment when installing sheet vinyl over a subfloor with visible defects, linoleum (the manufacturer specifies it), or laminate over a subfloor with surface variation greater than 1/8" over 6 feet. Skip the underlayment for ceramic tile (use cement backer board instead), engineered hardwood floating installs, and click-lock LVT over a flat subfloor.
Can I use CDX plywood for a kitchen subfloor?
Yes — CDX is the right call for kitchen subfloors. Kitchens see periodic spills, dishwasher leaks, and elevated humidity, and CDX tolerates occasional wetting where OSB swells permanently. Spec 23/32" or 3/4" tongue-and-groove CDX with an Exposure 1 stamp and an APA span rating matched to the joist spacing (24/16 for 16" oc, 32/16 for 19.2" oc). Construction adhesive on the joist tops plus subfloor screws every 6" perimeter, 12" field.
What is the best plywood for a bathroom subfloor?
23/32" or 3/4" tongue-and-groove CDX with an Exposure 1 stamp. Bathrooms are the highest-moisture room in a typical residential floor system, and the CDX premium over OSB pays back in moisture margin. For the tile floor itself, install 1/4" or 1/2" cement backer board over the CDX subfloor as the tile substrate. Do not use plywood underlayment under tile — plywood expands and contracts with humidity and the tile grout cracks every season. Cement backer board is the only correct tile substrate.
Do I install subfloor with screws or nails?
Either works if matched to the panel and the joist material. Subfloor-specific screws (typically #8 x 2-1/2" deck-rated or similar) give the best long-term holding and lowest squeak rate. Ring-shank nails (8d or 10d, hot-dip galvanized) are an accepted alternative that frames faster. Drywall screws are the wrong fastener — they snap under cycling floor loads. APA spec is 6" perimeter, 12" field for either fastener type. Construction adhesive on the joist tops before the panel goes down is non-negotiable for squeak control.
How long does a plywood subfloor last?
Properly installed CDX plywood subfloor lasts the structural life of the house — 75 to 100+ years — assuming it stays dry. Subfloor failures almost always trace to specific moisture events (plumbing leaks, roof failures, foundation moisture intrusion) rather than to age. OSB has a similar structural life when kept dry, but the failure mode after sustained wetting is faster and harder to recover from. Edge-sealing the panels at sheet joints during installation and maintaining moisture control under the floor (vapor barrier, conditioned crawlspace) extends life on both materials.
