Can You Tile Over a Wooden Floor? What Changed in 2024

The short answer to can you tile over a wooden floor is yes, but not the way it was done for decades, and not straight onto the boards. Since May 2024 the British Standard that governs floor tiling has stopped treating plywood and timber as a surface you bond tiles directly to. You now need something in between: a tile backer board, an uncoupling mat or a reinforced tanking system. Get that wrong and the tiles will crack or lift, usually within a couple of winters.

We tile over suspended timber floors regularly across Bromley and south east London, mostly in Victorian and Edwardian terraces where the ground floor is softwood boards on joists. The tiles are almost never the problem. What sits underneath them is.

What changed in BS 5385-3 in 2024

BS 5385-3 is the British Standard code of practice for internal and external ceramic and mosaic floor tiling. It was revised in May 2024, and the revision changed the single most common domestic detail in the trade.

Before, a competent tiler could overboard a timber floor with WBP plywood, prime it and tile straight onto the ply. That is no longer the recommendation. BAL’s technical note on tiling to timber floors states it plainly: as of May 2024, plywood and timber is no longer a suitable base for floor tiling directly to BS 5385-3:2024. Where you are tiling on a wood-based sheet or board, the standard now calls for an intermediate layer.

Walls went the same way earlier. The Tile Association notes that timber is no longer considered a suitable substrate under BS 5385 Part 1:2018, the wall tiling standard.

Test the floor before you think about tiles

Rigid finishes fail because the thing underneath them moves. A timber floor can feel completely solid underfoot and still deflect enough to crack a tiled surface, because you cannot feel a few millimetres of sag across a room.

The accepted minimum before ceramic tiles go down is a deflection of no more than L/360 of the span, and L/720 for natural stone, which is far less forgiving. BAL’s worked example is useful: with joists spanning 3.05m between supports, and 135kg applied at the centre, the floor should not drop more than 7.6mm relative to the ends.

Two things are worth knowing before you accept a floor as “fine”. The draft National Annex to BS EN 1990, the structural design Eurocode, sets a tighter value of L/500 or better for rigid flooring such as ceramic tiles. And the Tile Association’s own document on tiling to sheet and board substrates records that failures have been observed even at L/600, which is why rigidity is judged on established construction methods and not on a single string-line measurement.

You can run the check yourself. Anchor a tight nylon string across the longest span of the room, measure the gap between string and floor at the centre, then load that spot and measure again. If the difference exceeds the allowance for the span, the floor needs stiffening, not tiling.

There is a load figure too. BS 5385-3:2024 asks that an existing timber base be examined to confirm it can carry the additional dead load of the tiling system, up to 0.8kN per square metre, plus the likely dynamic loading, without excessive deflection.

Getting the boards right

If the floor passes on rigidity, the boarding is the next decision. The standard’s requirements are specific:

15mm minimum. BS 5385-3:2024 recommends a sheet or board of at least 15mm thickness. Thinner ply is a false economy and the most common cause of a failed timber-floor job.
Screwed at 300mm centres. Fix boards to the joists and to noggins at 300mm centres with countersunk screws long enough to bite properly into the timber. Check for pipes and cables first; a screw through a heating pipe under a newly tiled floor is a very expensive mistake.
Exterior grade, not any old sheet. Use exterior grade WBP plywood or marine grade plywood for overlaying an existing floor. BAL’s guidance warns that several timber boards on the market will not accept a rigid tile finish at all, so check what the board manufacturer actually says before you buy.
Condition the boards. They should be left to reach a moisture content appropriate to the room before fixing, or they will move after the tiles are down.
Seal the underside and edges. Sealing the lower face and edges, for example with an SBR bonding agent, reduces moisture pick-up from below and the warping that follows.
Stagger the joints. Where a second layer or a backer board goes over plywood, it should be fixed at 300mm centres so the joints in the two layers do not coincide.

For existing timber floors, BS 5385-3:2024 is stricter than most homeowners expect. Its recommendation is that existing boards are removed and the floor stiffened with noggings and joist support sleeper walls, after which you follow the rules for a new timber base.

The two routes that comply

Once the timber deck is sound, there are two accepted ways to get tiles on it.

Option one: a tile backer board. A proprietary board resistant to moisture and thermal movement, screwed or bonded over the plywood to the board manufacturer’s instructions. This adds the most height but is the most forgiving system.

Option two: an uncoupling mat. Thinner, quicker, and acceptable provided the timber floor is the correct grade, sufficiently dry, rigid and stable, able to carry static and dynamic loads without deflection, ventilated below, flat and level to SR1, and securely screwed to the joists at 300mm centres including any cross-noggins.

One point gets misunderstood constantly. An uncoupling mat does not fix a bouncy floor. BAL’s guidance on deflection is explicit that an uncoupling system cannot compensate for vertical movement in the floor; what it does is absorb limited lateral movement so it is not transmitted into the tile bed. Our guide to decoupling matting covers how the systems differ. If the joists deflect, the mat will not save the tiles.

Preparation before either option: sand the timber to remove varnish, lacquer or any other surface coating, then prime with two coats, applying the second at 90 degrees to the first and letting each dry. Bed the tiles in a flexible cement-based adhesive at a solid 3mm to 6mm, with no voids left underneath, using the technique in our guide to applying tile adhesive. Voids under a floor tile are where cracks start.

Bathrooms, wet rooms and the rot risk nobody mentions

Tiling a timber floor makes it far less permeable than bare boards. That matters more than it sounds. BAL’s note warns that laying tiles over timber can raise the moisture content of the wood enough to create conditions suitable for fungal attack, dry rot included, because the surface can no longer breathe. Before anything goes down, confirm that underfloor ventilation is adequate and that damp proof courses are correctly located.

BS 5385-3:2024 goes further and does not recommend timber as a substrate for floor tiling in wet, frequently damp or high humidity areas at all. In a shower area or wet room the floor should be tanked so no water reaches the timber, whatever else is specified. If you are planning a wet room over a suspended timber floor, treat the waterproofing as the main job and the tiling as the finish.

Movement joints, grout and the details that stop cracks

Timber moves seasonally, so a tiled timber floor needs somewhere for that movement to go. Movement joints on these installations should be at least 6mm wide and run the full depth of the tile and adhesive bed. BS 5385-3 places them:

over any existing or structural movement joints
around the perimeter of the floor, and where tiling meets columns, kerbs, steps or anything fixed to the base
in large areas, dividing the floor into bays no greater than 10m by 10m
on suspended floors, in smaller bays than that, with extra joints over supporting walls and beams
where the floor sees significant temperature change, in bays no larger than 40 square metres with no edge longer than 8m

Grout joints should be at least 3mm. Porous tiles are worth sealing before grouting so the grout does not stain the face. Perimeter joints can be filled with a flexible sealant rather than grout.

When it is cheaper to take the floor up

Overboarding is not always the sensible answer. Add a 15mm sheet, a backer board and a 10mm tile with adhesive and you can be 30mm or more above the old boards, which means doors that will not close, a step at every threshold, and skirting that no longer sits down properly. On a ground floor where the joists are undersized or the sleeper walls have moved, taking the boards up and laying a new base is often the better job and not much dearer once you have priced the boarding, mat, adhesive and the extra fittings against our tiling cost per square metre figures.

Frequently asked questions

Can you tile directly onto floorboards?

No. Individual floorboards move independently and BS 5385-3:2024 does not accept timber as a direct base for floor tiling. Boards need overboarding with a rigid sheet of at least 15mm, and then a backer board, uncoupling mat or reinforced tanking layer on top of that before tiles go down.

What thickness of plywood do you need under floor tiles?

15mm is the minimum recommended in BS 5385-3:2024, in exterior grade WBP or marine grade plywood, screwed to joists and noggins at 300mm centres. Since the 2024 revision, tiling directly onto that plywood is no longer the recommendation, so budget for the intermediate layer as well.

Will an uncoupling mat fix a bouncy floor?

No. Uncoupling mats deal with lateral movement between the substrate and the tiles. They do nothing for vertical deflection. If the floor drops more than the allowance for its span under load, the joists need stiffening with noggins or additional support before any tiling starts.

Can you tile over chipboard?

Treat it as a no unless the board manufacturer states otherwise in writing. BAL’s guidance is that several timber boards sold for flooring will not take a rigid ceramic finish, and standard flooring chipboard swells irreversibly if it ever gets wet, which in a kitchen or bathroom is a question of when rather than if.

Do you need flexible adhesive on a timber floor?

Yes. A flexible cement-based adhesive, laid as a solid bed of 3mm to 6mm with no voids, is what accommodates the small seasonal movement of the timber below. Standard non-flexible adhesive on a timber base is one of the reasons older jobs come loose.

How much height does tiling a timber floor add?

Add up the boarding, the backer board or mat, the adhesive bed and the tile. That total decides whether internal doors need trimming and whether you get a step at the threshold, so measure it before you order.

Getting it done properly in Bromley

Tiling over timber is not a job to judge by the quote alone. Ask what is going between the boards and the tiles, ask what the deflection check showed, and ask where the movement joints are going. A tiler who can answer those three questions is working to the current standard. You can see the rest of our work and the jobs we take on at Bromley Tilers.

The technical sources behind this article are worth reading if you are specifying the work yourself: the Tile Association’s technical FAQs and BAL technical note TN 23.24, Tiling to Timber Floors.

020 8058 5574

contact@bromleytilers.co.uk