Laying laminate on floorboards: prep, direction and when to board over

You can lay laminate on floorboards, and a sound timber floor is the easiest subfloor to work with. Upstairs there is nothing to wait for: no slab to dry out, usually no membrane, and rarely any levelling compound. The work is all in the prep, and it comes down to four things. Screw the old boards down so nothing moves, check they are flat to about 3 mm over 1 m, run the new floor across the old boards rather than along them, and only reach for hardboard or plywood if the timber fails that flatness check. The same job applies to vinyl plank and engineered wood over floorboards. Skip the screwing and you will hear about it every time you walk across the room, because once the laminate is down, the boards underneath are out of reach.

Can you lay laminate straight onto floorboards?

Usually yes. Laminate is a floating floor: the boards click to each other, not to the timber below, so nothing has to be fixed and the floorboards only have to be dry, still and flat. What disqualifies a floor is movement and moisture, not age. Check in this order:

• Lift one board near an outside wall and look into the void. It should be dry, cobwebby and moving with air. Wet, musty or crumbling timber is a repair job, not a flooring job.
• Count the airbricks in the outside walls, which are what ventilate a suspended ground floor, and clear anything growing over them. Never block or cover one while fitting a floor.
• Take a moisture reading with a timber meter, which should come in under about 12 percent. Higher than that means the void or the room is holding water, and the cause needs finding first.
• Walk the room in socks. Boards that flex, click or drop under your weight are loose, and that is the next job.

How do you prepare old floorboards?

By fixing them down properly. It is the noisiest problem in the room and the easiest one to solve while the floor is still open. Use screws rather than nails, since nails are what worked loose in the first place.

Then test the result with a straight edge and a torch, in several directions across the room, exactly as you would on a slab. Light showing under the edge is a dip. Laminate tolerates roughly 3 mm over 1 m, and underlay does not change that: at 2 to 3 mm thick it compresses rather than fills, so a board bridging a hollow flexes every time it is stepped on until the joints work loose. That is the first mistake on our list of ten for a reason.

Do you need hardboard or plywood over the floorboards?

Only when the boards fail on their own. An overlay is worth real money and about 17 mm of height, so it is a fix for a specific problem rather than a default step:

Plywood at 6 mm is the more forgiving choice: it is stiff enough to bridge what it spans, whereas thin hardboard follows the shape of what is under it and needs the boards to be nearly right already. Screw or ring-shank nail the sheets down at about 150 mm centres, stagger the joints so no four corners meet, and leave a 2 mm gap between sheets. Never use a thick soft underlay instead: the underlay guide covers why extra foam over a dip makes the floor worse rather than better.

Which way should the laminate run over floorboards?

Across the old boards, at 90 degrees to them. Two reasons: the new joints never land in the gaps between the old boards, and each new board spans several floorboards rather than following one, so any small residual movement is shared out instead of concentrated.

That inverts the rule most people half remember. Solid wood nailed to joists must run perpendicular to the joists, which means along the old boards. A floating laminate floor is not structural, so it goes the other way:

That last row is the useful one. If you have boarded over the floorboards, the constraint disappears and direction goes back to being a visual decision: towards the main light, along the longest wall, straight through doorways. The direction guide works through those trade-offs, including the narrow-room and hallway exceptions.

Does a floorboard subfloor need a vapour barrier?

It depends entirely on what is under the floorboards, and getting it backwards causes damage either way:

• Upstairs, over a heated room, no barrier. Nothing below is pushing moisture up, and a sealed sheet on a timber deck can trap the small amount of moisture the timber does carry. Standard 2 to 3 mm foam underlay is all it needs.
• On a suspended ground floor over a ventilated void, use one, because the void carries damp outside air all year. Either a combined underlay with a built-in barrier, or a separate polythene sheet beneath a standard one.
• Whichever you have, the airbricks stay clear. The void has to keep breathing, and blocking its ventilation to make a room feel warmer is how dry timber becomes wet timber.

Concrete is the opposite case, where the membrane is never optional and comes with a drying test and often a bag of levelling compound. The concrete subfloor guide covers that in full if you are working on a ground floor slab instead.

What changes at the edges and the doors?

Height, mostly. Laminate at 8 mm on 3 mm underlay lifts the floor about 11 mm, and a 6 mm plywood overlay takes that to nearer 17 mm. That is enough to matter at every edge of the room:

1. Internal doors may need 5 to 15 mm taken off the bottom. Check the clearance with a laminate offcut and underlay sample before you commit.
2. Doorways between rooms need a threshold strip sized for the new height, and the boards should run through the opening in one direction wherever the layout allows.
3. The expansion gap stays 8 to 12 mm on every side regardless of subfloor, with spacers against every wall and nothing screwed through the boards. The expansion gap guide has the full rules for pipes, thresholds and long runs.
4. Skirting or beading goes to the wall, never through the floor, so the trim hides the gap and lets the floor move underneath it.

Get the prep and the quantities settled in the same sitting. Measure the room, plan where the first and last row fall so the final strip is not a sliver, and draw the room in the layout planner to get the cut list and pack count before you buy, or run the numbers through the laminate calculator if the room is a plain rectangle. The screws and the straight edge are an afternoon; a floor laid over boards that were never fixed down is a weekend you get to repeat.