You'll never see your subfloor once the new floor is down, which is exactly why it's the easiest place for an installer to cut corners. Nearly every floor problem we're called to fix — squeaks, gaps, soft spots, planks that separate or click — started with a base that wasn't ready.
Proper preparation starts with inspection: checking flatness with a long straightedge, finding loose or damaged panels, and testing moisture in both wood subfloors and concrete slabs. Manufacturers set flatness and moisture limits for a reason, and ignoring them can void the product warranty.
Then comes the work: replacing damaged plywood, screwing loose sheathing down to the joists to stop squeaks, grinding high spots, filling low spots with leveling compound, and installing a moisture barrier where it's needed. Over concrete, the right underlayment matters as much as the floor itself.
Before you hire anyone, ask how they'll check the subfloor and what's included if they find problems. At One Star Flooring, subfloor inspection is part of every free estimate, and prep is itemized in your written quote — because strong floors start where it matters most.