Services in the floor zone
Running Pipes, Cables and Ducting Through a Screed Floor
Plumbers and electricians often want to use the floor zone. Here is how services can live inside a pumped screed without cracking it or being lost under it.
Services on the slab? Send us a photo
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Almost every renovation and extension we pour has something other than heating pipe on the slab: a cold feed to a kitchen island, a waste run to a new cloakroom, a data duct to a home office, a cable to an outside socket. The question we are asked on survey is always the same — can that stay where it is and go under the screed?
Usually it can. Pipework can be set into the screed provided it has been insulated and pressure-tested first, and any pipe or cable that crosses the isolation layer is sleeved so it does not form a rigid bridge between the floor and the structure. What matters is depth, fixing and testing — and deciding all three before the pump arrives rather than on the morning of the pour.
This guide is about services that are not underfloor heating. Heating loops have their own rules for cover and clipping, which we cover on the underfloor heating pages linked at the bottom.
Why a service run matters to the screed
A liquid screed is a thin, continuous slab. Anything that sits proud of the insulation reduces the thickness above it, and a pipe or duct running across the room creates a line where the section is suddenly shallower. That line is where a crack wants to form, and it is also where a floor covering can telegraph the shape underneath months later.
Rigid connections are the second issue. On a floating or unbonded build-up the screed is meant to move independently of the walls and slab. A copper pipe fixed hard to the substructure and rising straight through the floor ties the two together; sleeving that penetration lets the screed move around it instead of snapping against it.
What we check on survey
- Where each run enters and leaves the room, and whether it rises through the finished floor
- The outside diameter of the pipe or duct, including any lagging, against the planned screed depth
- Whether the run crosses heating loops, and at what point
- How it is fixed down — loose runs float up in a fluid screed
- Who has pressure-tested water and heating pipework, and whether the certificate is on site
- Whether a cable needs to stay accessible later (a duct with a draw wire) or can be buried permanently
Getting services ready for pour day
- 1
Agree the route
Services run in straight lines between walls where possible, not diagonally across the middle of an open-plan floor where the screed is working hardest.
- 2
Insulate and test
Water pipework is insulated and pressure-tested before it disappears. Once screed is poured over a leak, the only repair is breaking the floor out.
- 3
Sleeve every penetration
Pipes and cables crossing the isolation layer or rising through the floor get a sleeve, so the screed is not locked to them.
- 4
Fix it down
Liquid screed is dense and fluid. Anything not clipped or weighted firmly will lift during the pour and end up too close to the surface.
- 5
Photograph the layout
A set of photos with a tape in shot tells the next owner — and the next electrician — where not to drill.
Rules of thumb from our own pages
| Situation | What we work to |
|---|---|
| Water pipe cast into screed | Allowed if insulated and pressure-tested first |
| Pipe or cable crossing the isolation layer | Sleeved, never a rigid bridge |
| Heating pipe cover, bonded Gyvlon | 30mm to top of pipe |
| Heating pipe cover, unbonded Gyvlon | 35mm to top of pipe |
| Typical UFH floor depth we quote | 50–65mm |
| Heating loops during the pour | Left under pressure (tested to 6 bar) |
When a service should come out of the floor zone
Some runs are simply too big for the depth available. A large waste pipe on top of the slab in a room with a shallow finished-floor height can leave almost nothing above it. In that case the honest options are to drop the pipe into the slab or insulation zone, reroute it along a wall, or raise the floor. We would rather tell you that on survey than pour a floor that cracks along the pipe line.
The same applies to junction boxes and fittings. A joint buried in screed is a joint nobody can reach. Keep connections outside the pour area, or bring them up into an accessible void, and only pass continuous runs under the floor.
Frequently asked
Services on the slab? Send us a photo
A picture of the floor with the pipe runs marked is enough for us to say whether the depth works before you book.