Can I lay laminate straight over existing floorboards?

A suspended timber floor is a good base for a floating floor in many houses and a poor one in others, and the difference is entirely about how flat and how fixed the boards are. It is also the base people most often skip preparing, because the boards look fine from standing height and the problems only appear once the new floor is down.

Safety

What you'll need

• screws suitable for the boards and joists
• a long straight edge
• underlay suited to timber subfloors
• a plane or a floor sander, for high edges (optional)
• hardboard or plywood, if overlaying (optional)

Step by step

1. Walk the whole floor and mark every creak and movement.Each one is a board that is not fixed properly to its joist. They all have to be dealt with, because a floating floor amplifies rather than hides them.
2. Screw every loose board down into the joists.Screws, not nails — nails work loose again. Check what is under each fixing point first: pipes and cables run in the void and often sit right under the boards.
3. Check flatness with a long straight edge in several directions.Look for cupped boards, high edges at the joints, and any general dip. The flooring manufacturer states the tolerance and it is smaller than most people assume.
4. Deal with high edges.Cupped boards have raised edges at every joint, and a floating floor laid over them rocks on the high points. A belt sander or a plane along the high edges is the usual fix.
5. Run the new floor across the old boards.At right angles to the boards below, so each new board bridges several old ones. Running parallel means the new joints follow the old joints and any movement in them.
6. Do not block the ventilation of the void.A suspended timber floor relies on airflow through the underfloor void to stay dry. Do not seal the airbricks and do not fit an impermeable membrane in a way that traps moisture in the timber.
7. Check the boards for damp and rot before covering them.Especially near external walls, under a bathroom and anywhere there has been a leak. This is the last time you will see them.
8. Fit underlay suited to a timber subfloor.It takes up small irregularities and reduces noise. On a timber floor you generally do not want a vapour barrier trapping moisture in the boards — check what the underlay is designed for.
9. Overlay with hardboard or plywood if the boards are too far gone.Where boards are badly cupped, gappy or uneven, a sheet overlay screwed down at close centres gives a flat continuous base. It adds height, so check doors and thresholds.
10. Leave the expansion gap all round as normal.The floor above is still a floating raft, whatever is beneath it.

Tips

• Lift one board before starting anyway — it tells you what is under the floor, whether there is damp, and where the pipes run.
• A floor that has been lifted repeatedly for plumbing work is often the worst offender for uneven, badly refixed boards.
• If the boards are attractive and sound, consider sanding and finishing them rather than covering them. It is often cheaper than a new floor.
• Hardboard should be conditioned before laying — it is supplied dry and expands when it takes up room humidity, which buckles it if it is laid straight from the merchant.

Common mistakes

• Laying over creaking, unfixed boards — The creak is board movement against a joist or a nail, and a new floor over it does not stop the movement — it just adds a resonant surface above it. The floor will creak from day one and there is no way to fix it without lifting everything.
• Running the new boards parallel to the old ones — The new joints tend to line up with the old board joints, so every movement, gap and cupped edge below is followed rather than bridged. Laying across spreads each new board over several old ones.
• Sealing the underfloor void with an impermeable membrane — A suspended timber floor stays sound because air moves through the void and dries it. Trapping moisture against the boards is how a sound floor becomes a rotten one, and the damage is invisible until it is serious.

If it doesn't work

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