The subfloor decides it, and it is the step everybody skips
Almost every laminate floor that fails, fails from underneath. The boards themselves are consistent and the click joints are good. What is not consistent is the thing they were laid on.
A floating floor is a single sheet resting on the subfloor, so it can only be as flat as what is beneath it. Most manufacturers want no more than about 3mm of deviation under a 2 metre straightedge. Anything worse and the floor bridges the dip and flexes there every time somebody crosses it, which works the joints apart. A click joint that has opened does not click back.
So the first job is a straightedge and a torch across the whole room. Self-levelling compound on concrete, screwed-down boards or a ply overlay on timber. It is a dull afternoon and it is the difference between ten years and eighteen months.
On concrete you also want a damp proof membrane, either separate or built into the underlay. Concrete gives off moisture for a very long time, and a floor sealed over it with nothing between is a floor that cups.
On a suspended timber floor you do not, and putting one there is actively harmful: it traps moisture against the joists, which need to breathe from below. Same product, opposite answer, and combined underlays make it easy to fit the wrong one without noticing.
Leave the packs in the room first
Around 48 hours, flat, still in the packs, in the room they are going into, with the heating at whatever it normally sits at.
Boards take up the moisture level of the room they are in. Do that before they are locked together and nothing happens afterwards. Do it after and the boards move while they are already joined, which is the commonest reason gaps appear between boards a few months later, and it is the first thing a manufacturer asks about on a warranty claim.
Setting out, and the wall that is not straight
Direction first, and one reason outranks the rest. On a suspended timber floor the boards run across the joists, never along them, because boards laid parallel with the joists sit between supports instead of crossing them. That is structural and it settles the question on its own.
Everywhere else the reasons are visual: along the longest wall generally looks best and cuts less, and running towards the main window hides the seams, because light travelling along a joint barely catches it while light crossing one picks out every single seam.
What matters more is that the first row has to be straight even if the wall is not, and almost no wall is. If you lay the first row tight to a bowed wall, every row after it inherits the bow and the far side of the room ends up visibly out. Set the first row to a line rather than to the wall, and scribe the board edges to follow the wall if the gap varies. It is hidden by the skirting afterwards.
Stagger the end joints as you go, at least 300mm apart row to row, and avoid letting them fall into a regular diagonal. Starting each row with the offcut from the end of the last one does most of this for you and wastes far less.
The gap, and the thing that quietly cancels it
Every edge needs 10 to 12mm of clear space: walls, door frames, pipes, hearths, kitchen units, anywhere the floor could push against something solid. The floor moves as one piece and it has to have somewhere to go.
And then here is the part that undoes it, invisibly, on a great many otherwise careful jobs.
Beading and scotia cover the expansion gap, and they must be fixed to the skirting, sideways, never downwards into the floor. A nail through the beading into the subfloor pins the floor edge in place, and a floor pinned at the edge cannot expand anywhere. You get the peaking you left the gap to prevent, a summer later, with no visible cause.
The same rule catches threshold strips screwed through the boards, and pipe collars fixed down rather than sitting loose. If anything holds the floor, the floor is no longer floating.
Doorways and the last row
At a door frame, undercut the frame rather than cutting the board around it. Lay an offcut face down as a height guide, run a flush saw along it, and slide the flooring underneath. A board scribed around an architrave never looks right and leaves no room to move.
Large areas and doorways between rooms usually want an expansion break with a threshold strip, because there is a limit to how much floor can behave as one sheet. Manufacturers state a maximum run and it is worth reading before laying through three rooms in one go.
The last row is nearly always ripped down the length, and it is rarely parallel, because the far wall is not parallel to the first one. Measure it at both ends and at the middle.
Working out the packs
Flooring is sold by the pack rather than by the square metre, so the number you want is packs and the coverage per pack varies between products. The flooring calculator handles that, along with the wastage allowance and why a herringbone layout needs considerably more of it.
If the skirting is coming off and going back on, the skirting calculator covers lengths and internal against external corners, and room area is the starting measurement for both.
Common questions
How flat does the subfloor need to be?
Flatter than most people check, and this is the step that gets skipped because it is the boring one. Manufacturers typically want no more than about 3mm of deviation under a 2 metre straightedge, and a floating floor bridging a dip will flex there every time it is walked on. That flexing works the joints loose, and once a click joint has opened it does not close again. Self-levelling compound on concrete or a plywood overlay on timber is the fix, and it is far cheaper than lifting a floor.
Do I really need to leave the packs in the room first?
Yes. Nearly all of them ask for around 48 hours flat in the room it is going into, still in the packs, with the heating at its normal setting, and it is the first thing a manufacturer asks about on a warranty claim. The boards take up the moisture level of the room before they are locked together instead of afterwards. Skip it and the boards move once they are already joined, which is the usual reason gaps open between them a few months later.
Which way should the boards run?
One rule beats the others and it is structural. On a suspended timber floor the boards must run ACROSS the joists rather than along them, because boards running parallel with the joists sit between supports instead of spanning them. That is not a preference and it overrides everything below it. After that the reasons are aesthetic: along the longest wall usually looks best and means fewer cuts, and running towards the main window hides the joints, because light travelling along a seam catches it far less than light crossing it.
What is the expansion gap for?
A laminate or engineered floor is floating, meaning it is not fixed down at all, and it expands and contracts with temperature and humidity across the whole width of the room as one sheet. It needs somewhere to go. That means clear space at every edge, typically 10 to 12mm, at walls, door frames, pipes, hearths and kitchen units. Without it the floor has nowhere to expand to, so it lifts in the middle and the joints peak, usually within the first proper summer.
Can I lay laminate over an existing floor?
Over tiles or vinyl that are sound, flat and dry, generally yes. Over carpet, never, because the softness lets the floor flex and the joints work apart. Over floorboards, only once they have been checked for movement and screwed down where they are loose, and usually with a plywood overlay if they are uneven. Whatever is underneath, the flatness requirement does not relax and neither does the need for a moisture barrier on anything solid.
Do I need underlay if the boards have some attached?
Not a second layer, and a lot of people add one anyway and make things worse. Boards with integral backing are designed to sit directly on the subfloor and doubling up gives a floor that feels spongy and works its joints. What you may still need is a separate moisture barrier over concrete, because integral backing is not always one. Check what the backing actually is rather than assuming it covers both jobs.