When a floor feels uneven or noisy, people often assume the whole base has to come out. In our experience most subfloors in South East London and Kent homes can be made ready for new flooring with the right preparation, and only a minority need structural work first. The difference matters, because preparation is a known cost that goes on the flooring quote, while structural repairs are a separate job that has to be finished before any fitter starts. This page sets out the signs that point each way.
Why the subfloor decides the result
Almost every flooring failure we are asked to look at, from planks lipping at the joints to adhesive letting go, starts underneath rather than in the floor covering. A new floor can only be as flat, quiet and stable as whatever it sits on.
That is why the survey matters more than the sample. Before we price a job we look at what the floor is made of, how flat it is, whether it moves, and whether there is moisture present, and each of those answers points to a different remedy.
Timber floors: usually overlay, sometimes more
Original floorboards flex between joists, cup at the edges and leave joint lines that show through thin coverings. For LVT, and for laminate over uneven boards, the usual answer is a plywood overlay: 6mm WBP ply screwed at 150mm centres, with staggered joints and sanded edges. On boards with a lot of movement, 12mm ply may be needed instead.
Loose boards are screwed down to the joists before anything goes over them. That cures squeaks permanently, whereas covering a squeaky floor simply buries the noise under a new floor that would have to come up to fix it. Carpet on a good underlay can often go straight onto sound, secured boards with no overlay at all.
- Boards cupped or gappy but firm: plywood overlay
- Boards squeaking: screw down to the joists first, then overlay
- Floor springy or bouncing underfoot: structural problem, fix before flooring
Concrete floors: level, damp or both
Concrete rarely needs replacing for a floor covering, but it often needs levelling. Humps from old hearths, dips where extensions join, and patched service runs are dealt with by a latex or cement based levelling compound over a primer.
Damp is the more serious question. Older slabs frequently lack a working membrane, so a hygrometer test comes before any impermeable floor. Above 75% relative humidity, a liquid damp-proof membrane goes down first. Musty smells, dark patches and white salt bloom on the surface are warning signs worth mentioning at the survey.
Signs you need more than preparation
A floor that is springy or bounces when you walk across it has joist or board problems that must be resolved structurally, not covered. A rigid new floor over a moving base will fail at the joints however well it is laid.
Existing tiles that sound hollow when tapped have come away from the base and need lifting rather than overlaying. Persistent damp that returns after a membrane, rot in boards or joists, or a slab that is breaking up are also problems to solve before flooring, and we will say so plainly rather than cover them over.
- Bounce or spring underfoot
- Hollow sounding tiles
- Soft, rotten or crumbling boards or joists
- Damp that returns after treatment
What preparation costs
Our subfloor preparation starts from 12 pounds per square metre. Typical figures are 10 to 18 pounds per square metre for latex levelling, 14 to 22 pounds for a 6mm plywood overlay supplied and fitted, and 8 to 14 pounds for a liquid damp-proof membrane. Lifting and disposing of old flooring adds 3 to 6 pounds per square metre plus tip charges.
Preparation also adds height: ply plus LVT can be 8mm to 10mm. We check doors, thresholds and kitchen plinths against the new level before fitting day, and we include the preparation we expect in writing on the quote.
Want this priced for your own rooms?
We measure, check the subfloor and give you an itemised written quote - free, with no obligation, across South East London and Kent.
Frequently asked questions
Can new flooring go over old floorboards?
Usually yes. Carpet can go over sound, secured boards; LVT and laminate over uneven boards need a plywood overlay, normally 6mm WBP ply screwed at 150mm centres.
How do I know if my subfloor is bad?
Springy or bouncing boards, hollow sounding tiles, rot, or damp that keeps returning point to work beyond normal preparation.
Does concrete ever need replacing for new flooring?
Rarely. It usually needs a moisture test, sometimes a damp-proof membrane, and often levelling compound, all of which are standard preparation.
Is plywood overlay part of your quote?
Yes. Where we expect to need ply or levelling we include it in writing, priced from 12 pounds per square metre for preparation.