Installation

Excavation, bedding and backfill

A trench must not affect the stability of the building. Trenches should not be open too long in advance of pipe laying and should be backfilled as soon as possible. Trench widths should be as narrow as practicable, but not less than the pipe diameter plus 300mm to allow adequate sidefill to be placed.

Deeper excavations should ideally incorporate a sub-trench.

Bedding is the layer of material underneath the pipe. The in-situ soil (as dug material) may be suitable, but it must be inspected to ensure there is no sharp material (i.e. broken bricks) or a particle size which is more than 20mm.

If the as-dug material is not suitable, a granular material with a nominal 10mm particle size to BS EN 1610 should be used.

The bedding material should be laid evenly along the bottom of the trench before any pipework is installed. The sidefill material must be the same as the bedding material, extend to the crown of the pipe and be thoroughly compacted.

When the pipes are to be laid in rock, compacted sand or gravel, or in very soft or wet ground the bedding should be a minimum of 100mm.

Shallow domestic drains

Pipes laid at depths less than 600mm (not under a road), should be protected against risk of damage by placing a layer of concrete paving slab or similar over the pipe.

Drains under solid ground floors

A trench should be dug out of compacted hardcore, and suitable material used for the bedding and backfill. Where a pipe passes through a wall or foundation, a lintel or sleeve should be built in to provide clearance around the pipe.

Granular material for bed & surround of PVCu drains and sewers

Granular material for bed & surround of PVCu drains and sewers