Can You Lay Water Pipes Under a Screed?

Why are pipes hidden in screed, and what are the risks?

Concealed routing keeps pipes out of sight, frees up space and protects them from accidental knocks. Dust does not collect on pipes in a screed, and the pipe sits in a stable environment.

There is also one major drawback: if the pipe leaks, you have to break open the floor. That is expensive and slow, so every detail of the installation should be treated as work that cannot be redone. Expansion is a separate problem: a hot-water pipe lengthens when heated and a cold one collects condensation, and without a protective layer both damage the screed or leave it damp.

Which pipes are suitable for embedding in screed?

The material has to meet four requirements: flexibility so it can be laid in one piece, low thermal expansion, corrosion resistance and durability. The following fit:

• cross-linked polyethylene PE-X and PE-RT: flexible pipe in coils, so the loop is laid without joints;
• multilayer (metal-plastic) pipe: acceptable if every joint is kept outside the screed;
• copper: reliable and laid in insulation, but expensive and requires soldering;
• corrugated stainless steel: it bends and absorbs expansion.

Black and galvanised steel are not recommended because of corrosion, nor is rigid polypropylene: it bends poorly, expands noticeably and needs many joints.

How do you lay a pipe in screed correctly?

1. Level the base and lay edge insulation tape around the perimeter of the room.
2. Roll the pipe out in one piece from the manifold to the draw-off point, with no joints within the screed.
3. Fit protective corrugated sleeving or foamed-polyethylene insulation over the pipe: it takes up expansion and protects against condensation.
4. Fix the pipe with clips or fixing tape so it cannot float up during the pour.
5. Bring every joint out to the manifold or to accessible inspection points.
6. Pressure-test above the working pressure, usually 1.5 times, and keep the pressure on until the pour is finished.
7. Pour the screed and let it gain strength before loading the floor.

Why are joints in a screed dangerous?

The great majority of leaks in concealed pipes occur at joints rather than in the pipe itself. Compression and threaded fittings loosen over time from temperature cycling and vibration, so they need to stay accessible for tightening. Burying such a fitting in concrete means planning to open the floor later.

If a joint in the screed is unavoidable, use only permanent methods: a press fitting or welding. It is better, though, to change the layout so that tees and couplings end up in a shaft, a manifold cabinet or under a removable hatch. Run hot and cold water in separate pipes, each in its own insulation.

What about HDPE pipe and the water service into the house?

PE100 polyethylene is not normally used for internal runs in screed: it is stiffer than PE-X, does not bend as easily to a small radius, and its compression fittings must not be buried in concrete. But it suits the incoming service that passes under the floor or foundation: the pipe is supplied in 50–200 m coils, so the service can be laid in one piece with no joints, inside a protective sleeve.

For water supply to GOST 18599-2001, PE100 SDR17 (PN10) or SDR11 (PN16) is suitable, and these are pipes we produce. The service ends where it enters the house, and the internal distribution is then made from materials intended for indoor systems.