Where this starts
A floating floor is not fixed down. The boards lock to each other and the whole assembly rests on an underlay, so it behaves as a single panel covering the room — and that panel changes size with the moisture in the air and in the subfloor beneath it.
THE EXPANSION GAP IS THE FIRST PLACE TO LOOK, and it is hidden. Every floating floor needs a gap at every edge — against walls, around pipes, at door thresholds, against a hearth or a kitchen plinth — sized to the run and covered by the skirting or a beading, never filled. When that gap is missing or has been closed up, the panel expands into the wall, has nowhere to go, and buckles upward. That is peaking, and the lift is often nowhere near the point where the floor is trapped.
PULL A BEADING OFF and look. If the board is tight against the wall, or the gap is packed with adhesive, grout or a run of silicone, the cause is found and the remedy is to release it rather than to relay anything.
WHERE IT SITS matters as much as the gap. Trouble at a doorway usually means a threshold that pins two rooms together into one oversized panel — a floating floor should be broken at doorways, and a continuous run through several rooms exceeds the length any manufacturer allows. Trouble at a kitchen usually means units or an island standing ON the floor and holding it down while the rest of it moves.
MOISTURE is the other half and it works in both directions. A slab still drying, a leak, or a plumbing weep under a unit pushes the panel to expand; a house heated hard through a dry winter shrinks it and opens the joints. The tell is whether the problem comes and goes with the seasons or arrived once and stayed.
What it could be, and what tells them apart
These are candidates to check against your own building, in the order they most often turn out to be the answer. None of them is a diagnosis of your situation.
No expansion gap, or the gap has been closed
Most commonPeaking or lifting somewhere in the field, with the board tight to the wall at one or more edges when a beading is lifted, often after skirting was refitted or silicone run round the edge.
How to check: Lift a beading and look for daylight between board and wall. Tight anywhere is enough to buckle the whole floor.
Moisture from the subfloor
Most commonExpansion and lifting that worsens over months rather than seasons, often over a concrete slab, sometimes with cupped board edges and a musty smell.
How to check: Tape polythene to the subfloor at an edge and check underneath after a few days. Moisture there means the floor is being fed.
The floor is pinned by something standing on it
CommonProblems around kitchen units, an island, a heavy wardrobe or a door threshold, with the rest of the floor apparently fine.
How to check: What is sitting on the floor rather than beside it. A unit fixed through the boards nails the panel to one point.
One continuous run too large for the product
CommonA floor that carries through doorways into several rooms or down a hallway without a break, with peaking near the middle of the longest dimension.
How to check: Whether the floor is broken at doorways. Manufacturers state a maximum run, and a continuous house-wide floor usually exceeds it.
Seasonal shrinkage opening the joints
CommonGaps that open in the heating season and close again in summer, spread evenly rather than at one place, with the floor otherwise flat.
How to check: Whether it is seasonal. Joints that close again in humid months are the panel breathing, not a failure.
The underlay or the subfloor is not flat enough
Less commonLocalised movement, a hollow sound or a springy patch underfoot, with joints working apart at that spot rather than across the room.
How to check: Lay a long straightedge on the floor and look for daylight. A dip lets the panel flex there until the joints give.
What to check, in order
The order matters — each step is here because of what it rules out for the ones after it.
- 1
It is the single most common cause, it is hidden by design, and one tight edge is enough to buckle a whole room.
- 2
A run carried through several rooms is one oversized panel, which exceeds what any manufacturer allows and peaks in the middle of its longest dimension.
- 3
Kitchen units, islands and heavy fitted furniture pin the panel at a point while the rest of it moves, and the damage appears somewhere else entirely.
- 4
It separates a trapped floor from a fed one, and only the second needs the subfloor dealt with before anything is relaid.
- 5
Gaps that open and close with the heating are the panel behaving normally; movement that arrived once and stayed has a source that has not been found.
The calculations behind this
Several of the causes above are a quantity that was specified or assumed. These compute them, with the formula and the standard behind each.
When to stop and get somebody in
- Where a polythene test shows moisture in a subfloor the floor is sitting on, since that is a damp-proof membrane question and governs everything laid over it.
- Where the lifting is over a large area or the boards have cupped through their thickness, which means the material has taken up water rather than merely expanded.
- Where the floor runs under fitted kitchen units that would have to come out, because releasing it is then a kitchen job rather than a flooring one.
- Where there is any sign of a leak — a stain, a soft patch near a dishwasher or a radiator valve — since the floor is the symptom and the water is the problem.
This page lists candidates to check, not a diagnosis — nobody has seen your building. If the symptom involves anything structural, read this first.