The Subfloor Flatness Standard for LVP, and How to Check Yours

What the tolerance actually says

The most common published tolerance for rigid-core LVP is 3/16 inch over a 10-foot span, often paired with 1/8 inch over 6 feet. Some products specify tighter numbers, particularly for glue-down installation. Your product's installation instructions are the authority; do not assume.

This is a flatness tolerance, not a levelness tolerance. A floor can slope consistently across a room and still be perfectly flat, and LVP does not care about slope. What it cares about is local deviation — dips and humps within a short span.

How to check it yourself

You need a 10-foot straightedge — a length of aluminum box section or a good level will do — and a set of feeler gauges or a tape measure you can read to a sixteenth.

• Lay the straightedge on the bare subfloor, not on the existing floor covering.
• Work in a grid: run it along the length of the room, across the width, and diagonally.
• At each position, find the largest gap between the straightedge and the subfloor and note where it is.
• Mark high spots and low spots directly on the subfloor with a pencil as you go.
• Pay extra attention at doorways, along walls, over joist lines, and where an addition meets the original structure.

Matching the correction to the finding

High spots are ground down. A concrete grinder with dust extraction handles trowel ridges, thinset, and slab humps; on plywood, a belt sander or a plane deals with a crowned panel edge.

Isolated low spots are filled with a cementitious patching compound feathered out to the surrounding surface. This is the right tool for a dip a couple of feet across, and the wrong tool for a whole room.

Widespread or complex low areas call for self-leveling underlayment poured over a primed substrate. It is more expensive and needs cure time before flooring, but it is the only sensible approach when the deviation is everywhere.

Squeaks and movement are a separate problem from flatness, and they need fixing first — screwing loose panels down to the joists before any leveling material goes on top.

What happens when you skip it

A floating floor over a dip is unsupported in the middle of the dip. Every footstep flexes the planks at the locking edge, which is the weakest part of the assembly. Over months that produces the classic symptoms: a hollow drumming sound, a click at each step, and eventually joints that separate or a locking edge that fails outright.

Over a high spot, the floor pivots. Planks rock, seams work against each other, and the wear layer above the high point abrades faster than the surrounding floor.

Neither failure can be repaired without lifting the floor and correcting the substrate, which is the entire prep cost plus the reinstall.