Lay Subfloor That Won't Lift: Stagger the Butts, Gap the Seams

The Problem

Subfloor fails in slow motion: panels butted tight swell with moisture and have nowhere to go but up, fasteners without ridges or threads back out over years of deflection, and butt joints stacked in a line make a hinge across the floor. All three mistakes are invisible under flooring until they're squeaks and humps.

The Technique

1. Stagger the butt joints. Adjacent rows' end joints stay at least one joist bay apart — two bays is significantly better.
2. Cut each sheet to split a joist. The panel edge lands on half the joist's thickness so the neighboring sheet has the other half to bear on.
3. Read the stamp. OSB is marked "This Side Down" — following it puts the rough face up. On a subfloor that's grip underfoot; on roof decking the rough side up matters even more.
4. Leave a 1/8" gap at every joint — it's code, and it's the pressure relief that lets a swelling panel push sideways instead of lifting. Tongue-and-groove edges set their own gap.
5. Glue and fasten. Run subfloor adhesive down every joist, then fasten five per joist per sheet: two at the sheet ends, three in the field. Ring-shank nails hold with their ridges; screws hold with their threads. The creator uses screws exclusively; either resists the back-out that plain nails allow.

What You'll Need

3/4" tongue-and-groove subfloor panels (OSB or plywood — OSB is cheaper, both work), subfloor adhesive in sausage or cartridge tubes, and ring-shank nails or subfloor screws.