No, you generally should not use soil pipe underground.
According to technical guidance, a soil pipe – typically identified as a black, white, or grey 110mm pipe used for carrying waste from toilets – is designed and intended for installation above ground.
Why Soil Pipe is Not Ideal for Underground Use
Soil pipes, while durable for above-ground applications exposed to weather and UV light, are often made from materials that may not withstand the specific pressures, loads, and soil movements encountered when buried underground. Underground drainage systems require pipes made from materials specifically engineered for that environment.
The Correct Pipe for Underground Drainage
The reference material explicitly states: "Once the soil pipework goes below ground, it should be connected to a terracotta foul water drainage pipe." While terracotta is mentioned in the reference, modern underground drainage systems frequently use other robust materials designed for burial, such as uPVC (unplasticized polyvinyl chloride) pipes specifically rated for underground drainage.
Here's a quick comparison:
| Feature | Soil Pipe (Above Ground) | Foul Water Drainage Pipe (Underground) |
|---|---|---|
| Typical Use | Carrying waste from fixtures above ground | Carrying waste buried beneath the ground |
| Location | Installed vertically or horizontally above ground | Buried underground |
| Material | Often PVC or similar plastics (e.g., 110mm) | Engineered for burial (e.g., uPVC, sometimes older terracotta) |
| Strength | Designed for flow and above-ground stresses | Designed to withstand earth loads, traffic loads, and ground movement |
Connecting Above and Below Ground Systems
The critical transition point is where the above-ground soil pipe meets the below-ground drainage system. This connection must be made using appropriate fittings that ensure a watertight seal and transition from the above-ground pipe material to the underground pipe material. This is typically done just before the pipe enters the ground or shortly after it passes through a wall or foundation.
For detailed guidance on setting up underground drainage systems, resources like an "Underground Drainage: Installation and Principles article" are recommended, as mentioned in the source material. Proper installation according to building regulations and manufacturer specifications is crucial for the longevity and effectiveness of your drainage system.
