Level a timber floor before laying new flooring

Check your floor for high and low spots, fix them properly, then confirm it is flat enough for your new flooring.

LF-01Clear the room and check the floor's conditionRemove furniture, old flooring, carpet grippers and skirting if it's coming off. Sweep the boards and look for obvious problems: damp staining, soft or crumbly wood, insect holes, or boards that flex underfoot. If you find rot or damp, sort that out before you think about levelling — levelling a damp floor just wastes materials.

LF-02Find every high spot and low spotLay a long straight edge across the floor in several directions — along the boards, across them, and diagonally — and slide a spirit level along it to spot dips and humps. Mark high spots and low spots with a pencil as you go, and note any boards that bounce or feel soft, which usually means a joist problem underneath rather than just an uneven board.

1 each · 2m aluminium straight edge

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1 each · Carpenter's pencil

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LF-03Check for cables and pipes before you lift or drill anythingCables and pipes can run under floors almost anywhere, especially near sockets, radiators and skirting lines, and a cheap detector can miss deep cables or ones in metal conduit. Before you lift a single board, find your stopcock — usually under the kitchen sink — and check it actually turns, so you can shut the water off fast if you hit a pipe. If you're screwing or drilling near a wall run or a radiator pipe run and you're not certain what's there, isolate the electrics at the consumer unit and turn the water off at the stopcock first.

1 each · Cable and pipe detector

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LF-04Lift boards at the marked problem areasUse a flooring bolster to prise up boards at your marked high and low spots, working along the tongue or nail line so you don't split the wood. Check the joists underneath: minor unevenness between joists is normal and fixable yourself, but a joist that's visibly sagging, twisted, split or rotten is a structural problem, not a levelling one. If a joist itself is damaged, get a builder or structural engineer to look at it before you go further.

RULES

1 each · Flooring bolster

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KNOW THE RULES

Replacing or significantly altering load-bearing floor joists is structural work and may need Building Regulations (Part A) sign-off — this is beyond a straightforward levelling job.

LF-05Screw down loose or squeaky boardsWhere a board moves or squeaks, drill a 3mm pilot hole through the board into the joist below to stop it splitting, then drive a countersunk wood screw into the centre of the joist. Do this at every joist the loose board crosses, not just one end. Skip nails — screws grip far better and won't work loose again over time.

1 box · 38mm countersunk wood screws (box of 100)

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1 each · 3mm HSS pilot drill bit

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LF-06Plane or sand down high spotsFor a proud board edge or a slightly high joist, work it down with a hand plane or an electric sander, always going with the grain. Check with the straight edge every few passes so you don't take off too much — it's easy to overdo it and create a new dip. Stop as soon as the straight edge sits flat with no rock.

1 each · 80-grit sanding belt (floor sander)

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LF-07Pack out low spots and dipsWhere a board sits low over a joist, glue and screw a thin plywood packer onto the joist to bring it up to the right height, checking with the straight edge as you go. For a shallow dip across the board itself rather than at a joist, use a flexible, timber-flooring-rated levelling compound — ordinary cement-based leveller will crack on a floor that flexes. Spread it with a notched trowel and feather the edges into the surrounding boards.

1 pack · Plywood packers, mixed thicknesses

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1 bag · Flexible timber-floor levelling compound (5kg)

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1 each · Notched trowel

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LF-08Overlay with plywood if the floor needs it across the boardIf the whole floor is uneven rather than just a few spots, screw sheets of 6mm-9mm WBP plywood over the entire surface instead of chasing every dip individually. Stagger the joints like brickwork, screw every 200-300mm into the boards and joists below, and leave a 10mm gap at the walls for expansion. Use the same care with cables and pipes as before — check with your detector before driving screws near any wall run.

4 sheet · 6mm WBP plywood sheet (2400 x 1200mm)

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1 box · 38mm floor screws (box of 200)

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LF-09Check the whole floor is flat enough for your new flooringRun the straight edge and spirit level across the full floor again in several directions. Most flooring manufacturers want no more than 2-3mm variation over a 2m length — check the packaging or fitting instructions for your chosen flooring, as it varies by product. Fix any spot that still fails this check before you lay anything on top.

LF-10Clean up and refit skirtingVacuum up all dust and debris, especially sanding dust and any leftover levelling compound crumbs, as these will show through thin flooring like vinyl. Remove any old nails or screw heads sticking up. Refit skirting you removed earlier, and make sure any airbricks or floor vents are still clear and uncovered.

2 each · Heavy-duty rubble sacks

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