How much will new flooring raise the floor?
Every layer you lay adds height, and only the old covering you take up gives some of it back. Tiles over a thin levelling compound typically add 15 to 25 mm, laminate on foam underlay about 10 mm, and a 50 mm screed with tiles 60 mm or more. It shows up at every door, at the next room and under kitchen plinths and appliances.
The calculator takes the layers you set up — screed or levelling compound, adhesive bed, decoupling membrane, underlay, tiles or boards — and stacks their thicknesses from the bottom up. The adhesive bed is worked out from how much powder goes on each square metre, so a bigger trowel notch or back-buttering shows up in the height too. When the subfloor is uneven, the screed is deeper at the low spots, so you also get a range from the high spot to the low spot.
Typical thickness of each layer
Typical values; your data sheet wins, and every layer can be changed:
- Self-levelling compound: 2 to 10 mm per pour; sand-cement screed 25 to 65 mm or more.
- Tile adhesive bed: about 3 mm with a 10 mm notch, 4 mm with a 12 mm notch and back-buttering.
- Decoupling membrane: 3 mm thin, 7 mm thick or for underfloor heating.
- Underlay: 1.5 mm for vinyl, 2 to 3 mm foam, 5 mm fibreboard.
- Tiles: 8 to 10 mm porcelain, up to 20 mm natural stone.
- Boards and planks: 2.5 mm glue-down LVT, 4 to 6 mm click vinyl, 8 to 12 mm laminate, about 14 mm engineered wood.
- Old covering taken up: sheet vinyl about 3 mm, laminate with underlay 10 mm, tiles with adhesive or carpet with underlay 12 mm.
The floor height formula
H_add = Σ layer thicknesses; ΔH = H_add − H_removed; undercut = max(0, Q − (G − ΔH))
G is the gap under the door today, Q the gap you want to keep (10 mm by default) and H_removed the old covering you take up. Adhesive beds are estimated from their coverage: 1 kg of powder per m² makes a bed of about 0.7 mm. The step at the doorway is ΔH minus any change on the other side.
Worked example
- Take up laminate and underlay, 10 mm. Lay 3 mm of self-levelling compound, tile adhesive at 4 kg/m² (a 2.8 mm bed) and 10 mm tiles.
- Added: 3 + 2.8 + 10 = 15.8 mm. Net raise: 15.8 − 10 = 5.8 mm.
- The door clears the old floor by 12 mm, so 6.2 mm is left. To keep 10 mm, take 4 mm off the door (3.8 mm, rounded up).
- The step to the next room is 5.8 mm — under 6 mm, so a flat threshold strip is fine.
How much to take off a door
Measure the gap between the bottom of each door and the floor that is there now, and enter it under the door. The calculator subtracts the net raise and shows the gap that is left. If that is less than the gap you want to keep — 10 mm by default — it tells you how much to undercut, rounded up to the next millimetre. Keep more where the door gap is the air path for ventilation or heating.
Undercut before the new floor goes down if you can, and trim the door frame and architrave at the same height so the flooring slides underneath instead of being scribed around them. A door that does not swing over the new floor can be switched off.
Thresholds between rooms of different height
Where the new floor meets a room that keeps its old floor, the step is the net raise. A common rule of thumb from accessibility guidance: up to 6 mm can be flush or covered with a T-profile, 6 to 13 mm needs a ramp (reducer) profile bevelled no steeper than 1:2, and anything higher needs a threshold or ramp — or a thinner build-up. If the next room is being redone too, enter how much its floor goes up and the step shrinks to match. The threshold strips themselves are on the list in the floor renovation calculator.
Frequently asked questions
How much do tiles raise the floor?
Porcelain tiles on adhesive add about 13 mm: 10 mm of tile and a 3 mm adhesive bed. Add any levelling compound or membrane underneath and subtract what you take up.
Do I have to cut my doors for new flooring?
Only if the gap left under the door is smaller than you want. Enter the gap you have now; if the floor rises by more than that gap minus about 10 mm, the door needs an undercut.
How much gap should be under an internal door?
About 10 mm above the finished floor is the usual minimum, and ventilation often relies on it. Check before you cut a door that has a bigger gap on purpose.
Should I undercut the door frames and architraves?
Yes. Cut the frame and architrave at the height of the new floor — use an offcut of the new floor on its underlay as a guide — so the floor slides underneath with its expansion gap.
What if the new floor is higher than the next room?
Use a profile that matches the step: flat or T-profile up to 6 mm, a ramp profile up to 13 mm and a threshold or ramp above that. If the step is too big, a thinner screed, underlay or tile brings it down.
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