Installation of Below-Ground and Above-Ground Drainage
Below ground
Installation starts with accurate setout: string line or laser, grade checked regularly, invert levels recorded as laid. Trenches are excavated to the designed width and depth, the bed prepared, pipes laid from the low end with sockets upstream, junctions set to the correct angle and orientation, and inspection openings placed so every part of the drain can be rodded. Backfill is placed in layers and compacted to specification, keeping the pipe alignment and grade intact.
Where cover is insufficient, concrete encasement or a slab is used. Where a drain passes under or through a footing, it is sleeved with clearance so building movement cannot shear the pipe. Connections to the public main require the network operator's approval and inspection, and the boundary connection is made with an approved fitting. Trench stops around structures prevent water tracking along the trench.
Above ground
Stacks must be plumb, adequately supported and braced, with expansion allowance on tall stacks, correct offsets and swept junctions. Penetrations through roofs and walls need durable, correctly flashed weathertight details. Vent terminals must terminate at the height and position required to avoid nuisance and to admit air. The overflow relief gully is critical: it must be set so its surcharge level is below the lowest fixture served and above the surrounding paving, so a blockage spills outside, never inside the building.
Traps
Laying to grade from the wrong end and accumulating error. Forgetting to record as-laid invert levels. Setting an ORG too high (sewage indoors) or buried (no relief). Supports too far apart on a tall stack. Failing to protect open pipe ends from debris during construction.
Rule of thumb: check grade every pipe length and again before backfilling - correcting a drain after backfill costs more than the entire original installation.