UFH design guide
Underfloor Heating Screed — The Complete Guide
Depths, mixes, first-heat schedules and the mistakes we see most often. Written for self-builders, main contractors and UFH designers.
Planning a UFH pour?
Name, phone, email — we'll reply the same working day with a fixed price.
Or call our landline on 01392 237700
UFH is the single biggest reason clients switch from sand-and-cement to liquid screed. The pipework encapsulates cleanly, the cover depth drops, and the heating system responds faster once you actually turn it on.
But there's a right way and a wrong way. Every issue we get called out to remediate — cracking, curling, popped tiles, UFH runs colder than the design — traces back to a decision made at spec stage. This guide walks the whole build-up.
Recommended cover depths over UFH pipe
| Build-up | Cover depth |
|---|---|
| Bonded to concrete slab | 30mm minimum over pipe |
| Unbonded (over DPM) | 35mm minimum over pipe |
| Floating (over insulation) | 40mm minimum over pipe |
| Suspended timber | 40mm cover + fibre-reinforced mix |
The full UFH + liquid screed sequence
- 1
Insulation
PIR or EPS200 to Building Regs U-value. All joints taped.
- 2
DPM
1200-gauge polythene, joints taped and lapped up walls.
- 3
Perimeter foam
10mm closed-cell foam around all perimeters and up-stands.
- 4
UFH pipework
Clipped to grid at design spacing. Pressure-tested to 6 bar and left under pressure through pour and cure.
- 5
Datum
Laser levels and datum pins to true finish level, minimum cover confirmed.
- 6
Pour
Cemfloor Therm or Gyvlon Thermio+ pumped and dappled.
- 7
48h no traffic
Cover with polythene, no wind, no heaters, no forced drying.
- 8
Cure & dry
Ambient control, moisture readings taken through cure. Anhydrite: sand laitance.
- 9
Commissioning heat
First heat cycle per manufacturer schedule — usually 7–21 days depending on chemistry.
- 10
Floor coverings
Only once RH is signed off and heat cycle complete.
The five mistakes we get called to fix
- Insufficient cover over pipes → shadow-lines and cracking above pipe runs
- Skipping the pressure test → pinhole leaks that only show weeks later
- Forcing drying with unvented heaters → curling and popped tiles
- Missing the first-heat commissioning cycle → thermal shock cracking on first winter
- Tiling before RH sign-off → adhesive failure, entire floor lifted
Get the pressure test, the cover depth and the commissioning heat cycle right and you'll never see us for a warranty visit. Skip one of the three and you probably will.
— Exeter Liquid Screeders
Frequently asked
Planning a UFH pour?
Send drawings and your UFH designer's spec. We'll cross-check the build-up and quote against the right screed for your programme.