Drainage Testing and Inspection Requirements

What This Requirement Covers

Below-ground drainage systems must be tested to confirm they are watertight and free from defects before they are backfilled and concealed. Approved Document H requires that all new drainage is tested, and Building Control will inspect the drainage at key stages during construction.

Key Requirements

Testing Standards

1. Drainage must be tested to BS EN 1610 (Installation and testing of drains and sewers)
2. Two types of test are used:

- Air test: A pressure of 100 mm water gauge is applied and maintained for 5 minutes; the pressure drop must not exceed 25 mm (for 100 mm pipes) or 12 mm (for 150 mm pipes) - Water test: The drain is filled with water to a head of 1.2 metres above the invert; the water level must not fall more than 6.4 mm in 5 minutes per metre of pipe length

When Testing Is Required

1. All new below-ground drainage before backfilling
2. Existing drains that have been extended or connected to
3. Drains that have been repaired or relaid
4. Building Control may also require a test of the existing drainage if there is reason to believe it is defective

Building Control Inspections

Building Control typically requires the following drainage inspections

1. Foundation excavation: Checking the drain route does not conflict with foundations
2. Drain laying: Inspecting the pipe gradient, bedding, joints, and connection points before backfilling
3. Testing: Witnessing or reviewing the drainage test results
4. Backfilling: Confirming appropriate backfill material and compaction

CCTV Surveys

1. CCTV surveys are not mandatory under Building Regulations but may be required by:

- The sewerage company (for build-over agreements) - Building Control (where drainage defects are suspected) - Mortgage lenders or insurers

1. CCTV surveys are also recommended when purchasing a property to check the condition of the existing drainage

Practical Compliance Tips

1. Carry out the drainage air test before backfilling; once the trench is filled, accessing a leaking joint is expensive
2. Ensure all joints are clean, properly aligned, and fully pushed home before testing
3. Keep the drainage test certificates for Building Control and for the building file
4. Notify Building Control before commencing drain laying so they can schedule inspections
5. Use appropriate bedding material (typically 10 mm pea gravel or granular material) and compact backfill carefully to avoid damaging the pipes
6. Mark the location of all inspection chambers and access points on the as-built drawing
7. Consider commissioning a CCTV survey after completion as a final quality check, particularly for longer runs or complex layouts