How the two differ in kind
A floating floor — laminate, engineered timber, click vinyl — is not fastened to anything. It rests on an underlay as a single large plate, held together at its joints, and it expands and contracts as a plate with changes in temperature and, more significantly, humidity. Everything about installing one follows from that.
The PERIMETER EXPANSION GAP gives the plate somewhere to grow. A continuous gap at every edge of the floor, concealed by skirting or a beading that is fixed to the WALL rather than to the floor, lets the field expand without pressing against anything. The requirement is continuous and it includes every place people forget: doorframes, which should be undercut so the floor runs beneath them; pipes coming through the floor, which need a collar rather than a tight hole; kitchen plinths and island bases; hearths; and the edges of any fixed item standing on the floor. A gap correctly left at the walls and closed at one doorframe is a restraint, and the floor buckles at it.
TRANSITION STRIPS address the other half. Expansion is proportional to LENGTH — a long run accumulates more total movement than a short one for the same change in conditions — so beyond a certain dimension the growth exceeds what any reasonable perimeter gap can absorb. Manufacturers therefore state a maximum dimension in each direction, and a floor larger than that has to be divided by an expansion joint with a strip over it, whether or not there is a doorway in a convenient place.
That is the part most often skipped, because a transition strip in the middle of an open-plan space looks like an admission of defeat. The alternative is a floor that tents.
The symptom of failing at either is the same: the floor lifts off the underlay in a ridge, peaks along a line, or rises at a doorway — which is why the diagnosis needs both to be checked.
The factors that actually differ
Show
| Perimeter expansion gap | Transition strips | |
|---|---|---|
| What it provides | Room for the field to grow, at every edge. | A break, so no single area accumulates more movement than a gap can absorb. |
| What drives the requirement | The floor's expansion coefficient and the humidity swing — stated by the manufacturer as a gap width. | LENGTH. Movement is proportional to run, so the manufacturer states a maximum dimension. |
| Where it applies | Every edge: walls, doorframes, pipes, plinths, hearths, fixed furniture bases. | Doorways, changes of material, and anywhere a run exceeds the maximum dimension. |
| The commonly missed case | Doorframes not undercut, and pipes with no collar — a single restraint defeats the whole floor. | An open-plan area longer than the maximum, where no doorway suggests a break. |
| How it is concealed | Skirting or beading fixed to the WALL, never to the floor — fixing through it defeats it. | A strip that covers the joint without clamping either side down. |
| Symptom when omitted | Tenting, peaking, and lifting at the restrained point. | Identical — which is why both are checked when diagnosing. |
| Underlay | Not related, though a compressible underlay does not substitute for a gap. | Not related. |
| Acclimatisation | Reduces how much movement occurs after laying, but does not remove the need for the gap. | Same. |
| Can one substitute for the other | No. A generous perimeter gap does not make an over-long run acceptable. | No. A strip every few metres does not excuse a floor hard against a doorframe. |
| When it is discovered | After the first seasonal humidity swing, which is months later. | The same, which is why neither is caught at handover. |
Which one, and when
Choose perimeter expansion gap when…
- Every floating floor, at every edge — this is not optional and it is not a judgement call.
- At doorframes, which should be undercut so the flooring passes beneath them.
- Around pipes, columns and anything else rising through the floor.
- Against kitchen plinths, island bases, hearths and any fixed item standing on the floor.
Choose transition strips when…
- At doorways between rooms, which is the conventional and convenient place for a break.
- Where a run exceeds the manufacturer's maximum dimension, whether or not a doorway exists there.
- At a change of flooring material, where two materials move differently.
- In long open-plan spaces and L-shaped rooms, where a single field would otherwise be too large.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Why does a floating floor lift in the middle of the room?
- Because it has grown and something is stopping it moving. The floor expands as a plate; if every edge has a gap, the growth is absorbed and nothing happens. If any edge is restrained — hard against a wall, pinched under a doorframe, tight around a pipe, trapped under a kitchen plinth, or nailed through by a skirting fixing — then the plate cannot move at that point, and the compressive force has to go somewhere. It goes upward: the floor lifts off the underlay, tenting in a ridge or peaking along a joint, usually some distance from the restraint rather than at it. That is why the diagnosis starts by finding the restraint rather than by looking at where the floor has lifted, and why a single missed doorframe can tent a floor several rooms away.
- How wide should the perimeter gap be?
- As the manufacturer states for that product, and the figure depends on the material and on the size of the floor rather than being a universal number. What sets it is how much the floor will move: the material's response to humidity — laminate and engineered timber differ, and vinyl responds more to temperature than to moisture — multiplied by the dimension of the run. So a larger floor needs a larger gap, which is one reason manufacturers state both a gap and a maximum area. The gap has to be continuous and it has to be maintained during installation, which is what spacers are for; they are removed once the skirting or beading is fixed. The other requirement is that whatever conceals it is fixed to the wall, never through the floor.
- When is a transition strip needed without a doorway?
- Whenever a run exceeds the manufacturer's maximum dimension, which in a modern open-plan layout happens regularly. Expansion is proportional to length, so a long continuous run accumulates more total movement than a short one, and past a certain dimension that movement exceeds what a perimeter gap can reasonably absorb — no gap wide enough to take it would be concealable by a skirting. Manufacturers therefore state a maximum in each direction, and a floor exceeding it needs an expansion joint with a strip over it, placed wherever is least conspicuous rather than where a doorway happens to be. It also applies to L-shaped and irregular rooms, where a break at the internal corner prevents the two legs of the floor fighting each other, and to runs continuing through an opening into another space.
- Does acclimatisation remove the need for a gap?
- No, and treating it as though it does is a common misunderstanding of what acclimatisation achieves. Leaving the flooring in the room for the stated period lets it come to equilibrium with the conditions it will live in, so the movement immediately after installation is small — which prevents the specific failure of a floor laid straight from a cold van and then shrinking or growing sharply in its first weeks. What it does not do is stop the floor responding to conditions afterwards. A room's humidity varies seasonally for the life of the building, with heating on in winter and off in summer, and the floor moves with it every year. The gap exists for that ongoing movement, not for the initial settling — so acclimatisation and the expansion gap are both required and neither substitutes for the other.
- What restraints do people forget?
- The ones that are not walls. Doorframes are the commonest: the flooring is cut tightly around the architrave instead of the frame being undercut so the floor runs beneath it, and that single point pins the whole run. Pipes rising through the floor, cut with a tight hole rather than an oversized one with a collar over it. Kitchen plinths and island bases, where the floor is run under the units and then trapped by their weight or fixings. Hearths and fireplaces. Heavy fixed furniture standing on the floor rather than on its own feet through it. Skirting or beading fixed down THROUGH the floor rather than to the wall, which pins it at every fixing. Any one of these is enough, and none of them is visible once the job is finished.
- Can a floating floor go under kitchen units?
- It depends on the manufacturer and it is a question to settle before the units are fitted, because it cannot be changed afterwards. The concern is that a run of units with a worktop and appliances is heavy enough to pin the floor at that point, so the floor beneath them cannot move — which either restrains the field or, if the floor shrinks, opens gaps at the joints that cannot close. Many manufacturers therefore specify that the flooring is not run under fixed units, with the units installed on the subfloor and the flooring butted to them with an expansion gap and a trim. Others permit running it through with conditions. Where the units are installed first, the floor's edge against them is treated as a perimeter and gapped accordingly.
- What about underfloor heating?
- It increases the movement and tightens every requirement, so the manufacturer's instructions for heated floors are a separate specification rather than a note. The floor now experiences a larger and faster temperature swing than an unheated one, so it moves more; the maximum area is often reduced and the gap increased. The other requirements are about the heating rather than the floor: a maximum surface temperature that the flooring can tolerate, which the floor sensor enforces; a commissioning heat cycle before the flooring is laid, so the screed's residual moisture is driven off; and a gradual start-up and shutdown rather than sharp changes. Not every floating floor is suitable over heating at all, and the ones that are state a maximum thermal resistance for the floor and underlay together.
- How do I fix a floor that has already tented?
- Find the restraint, release it, and let the floor relax — which usually works if it is caught before the joints are damaged. The sequence is to identify where the floor is pinned rather than where it has lifted: lift the skirting or beading and check the gap at every wall, check the doorframes and any pipe or column, and check whether the beading was fixed through the floor. Releasing the restraint — trimming the floor back at that point, undercutting the frame, enlarging a pipe hole — often lets the tenting settle within days as the plate redistributes. Where it does not, or where the joints have been forced apart or the locking profiles damaged, the affected boards have to be lifted and relaid. The one thing that never works is weighting the ridge down.