Below Ground Drainage
QA inspection checklist

Pipework

1. 1.

   Pipe material and diameter match design
   What to look forPipe material per design — vitrified clay (BS EN 295), PVC-U (BS EN 1401), polypropylene (BS EN 1852), or twin-wall HDPE for highway drainage. Diameter and class (SN8 typical for adoptable) verified. Flexible joints with EPDM seals — not solvent welded for buried foul.
   Acceptable whenPer Sewers for Adoption 7th Ed / Building Regulations Approved Document H: minimum 100 mm dia foul, 75 mm dia rainwater. Class SN8 stiffness for buried pipe. Flexible joints to BS EN 1610. Material BBA / WRc certified.
   StandardApproved Document H. Sewers for Adoption 7th Edition / Code for Adoption (Water UK 2020). BS EN 1610:2015 — Construction and testing of drains and sewers.
   Common defectsPipe undersized — surcharging in heavy rainSolvent-welded joints in buried foul — no movement, crackingSN4 instead of SN8 — pipe deflects under fillMixed materials in same run without proper transition couplerNo certification documentation
2. 2.

   Falls correct

   Record: Fall (1 in ?)
   What to look forFalls measured along pipe length with laser or boning rod. Foul drains typically 1:40 (100 mm) or 1:60 (150 mm) minimum. Surface water 1:100 minimum. No back-falls, no flat sections, no over-steep falls (> 1:10 risks self-cleansing failure on solids). Invert levels at manholes match drawing.
   Acceptable whenPer Approved Document H1 Section 2: foul 100 mm pipe ≥ 1:40 (with at least 1 WC); 150 mm ≥ 1:60. Surface water ≥ 1:100. Maximum fall typically 1:10 to maintain self-cleansing. Invert level tolerance ±10 mm.
   StandardApproved Document H1. BS EN 752:2017 — Drain and sewer systems outside buildings. Sewers for Adoption 7th Ed.
   Common defectsFall flatter than spec — solids deposit, blockageBack-fall — water ponds, solids depositOver-steep — water races ahead of solidsStep at manhole exceeds drop-shaft designNo level record — invert levels assumed
3. 3.

   Bedding and surround correct
   What to look forPipe bedding per design class — typically Class S (full granular surround) for plastic, Class B (granular bed and side fill) for clay. Bedding material 10 mm pea gravel, 100 mm minimum below pipe. Side fill compacted in 100 mm layers without disturbing pipe.
   Acceptable whenPer BS EN 1610 / Building Research Establishment guidance: bedding material 4-10 mm clean granular; bed depth 100 mm minimum; side fill compacted in layers ≤ 200 mm to top of pipe; cover 300 mm minimum to first granular fill, 100 mm above pipe protected.
   StandardBS EN 1610:2015. Approved Document H. CIRIA C698 — Site handbook for the construction of SuDS.
   Common defectsNo granular bedding — pipe rests on lumps in trench bottomSide fill not compacted — pipe deflectsCover < 300 mm under road / drive — risk of crush from vehiclesSharp stones in surround — point load on pipePipe sits on drainage spigot of fitting (not in line)
4. 4.

   Manholes/chambers constructed to specification
   What to look forChamber type per design — precast concrete (BS 5911), in-situ brick, or modular plastic (Polypipe, Wavin). Chamber size matches duty (typically 1200 mm dia for adoptable up to 1.5 m deep). Channels and benching to falls. Step irons / safety-chain ladder per H&S.
   Acceptable whenPer Sewers for Adoption / BS EN 1917: chamber dia per depth — 1200 mm to 3 m, 1500 mm to 6 m. Benching slope 1:12 minimum to channel. Cover slab and frame to BS EN 124 Class D400 in highway. Step irons to BS EN 13101.
   StandardBS EN 1917:2002 (precast concrete chambers). Sewers for Adoption 7th Ed. BS EN 124-2 (covers and frames). BS EN 13101 (step irons).
   Common defectsChamber under-size — not safe for entryBenching incorrect — solids deposit on shelfWrong cover class — D400 needed in highway, B125 fittedNo step irons or wrong centres — entry hazardBrick chamber not pointed flush — tracking through joints

Testing

1. 5.

   Air test or water test passed
   What to look forAir test (low pressure) or water test (50 mm head) on each section after bedding and before backfill. Pressure / water level monitored over test duration. No drop beyond allowable. Records signed by drainage engineer.
   Acceptable whenPer BS EN 1610 and Approved Document H: water test — fill to 1.5 m head (or 50 mm above invert at upstream end), maintain for 30 min, top-up volume ≤ 0.05 L/m for 100 mm pipe. Air test — 100 mm w.g., drop ≤ 25 mm in 5 min. Test before backfill.
   StandardBS EN 1610:2015 — Construction and testing of drains and sewers. Approved Document H1. Sewers for Adoption 7th Ed.
   Common defectsJoint leaks — flexible seal not seatedWater test fails after pipe filled with water — pipe was OK to start, joint leakDrop in air test > 25 mm — pinhole somewhereTest made after backfill — leaks hiddenNo record — disputes over pre-existing damage
2. 6.

   CCTV survey completed
   What to look forCCTV survey by competent operator (WRc certified). Continuous footage along each pipe length with chainage and grading. No structural defects, no debris, no displaced joints, no infiltration. Report identifies any defects with WRc Manual of Sewer Condition Classification grade.
   Acceptable whenPer WRc MSCC5 / OS19x: structural condition Grade 1 (excellent) — Grade 5 (worst). New installations expected Grade 1 throughout. Service condition (debris, infiltration) similarly graded. Adoption requires Grade 1 structural and ≤ Grade 2 service.
   StandardWRc Manual of Sewer Condition Classification (MSCC5). Sewers for Adoption 7th Ed. WRc Operational Specifications (OS19x).
   Common defectsJoint displacement (J grade > 1) — not all joints fully homeDebris in pipe — not jetted before surveyCamera passes through inverted siphon (water-filled) — grading impossibleSurvey not signed off by competent CCTV operatorDefective sections not flagged for remediation
3. 7.

   As-built drainage plan provided
   What to look forAs-built drainage plan showing actual installed positions, invert levels, pipe materials, sizes, falls, and chamber details. Differs from design drawings if changes made on site. Plan deposited with sewerage undertaker for adoption. Held in O&M.
   Acceptable whenPer Sewers for Adoption: as-built drawing in CAD format showing all underground services, levels per OS datum. Adopted public sewers handed over with full asset register. Building Regulations require drainage plan in completion documents.
   StandardSewers for Adoption 7th Ed. Approved Document H. Section 104 Water Industry Act 1991 (adoption agreement).
   Common defectsDrawing shown as-design, not as-built — adoption failsNo depth / level data — future works dig blindConnection points to existing not surveyed — disputes with utilityDrawing scale or datum incorrectChanges (e.g. additional rodding eyes) not on drawing

Run this inspection on a phone

The same 7 checks, with the guidance a tap away, photos against each fail, measurements recorded, an NCR raised automatically and a branded PDF at the end. Signed on site. 14 days free.