1) What is alternative evidence?
Alternative evidence may be used as an alternative to witnessing the drain test
2) Installation of drainage
a) By submitting this drainage alternative evidence, the person signing this document is confirming that the drainage installation complies with the manufacturers’ recommendations and guidance, the relevant British Standards or European Standards, and the Building Regulations as amended.
b) In practical terms, the person signing this document is confirming the suitability (where relevant) of the following:
1) materials used, including suitability of pipework for above ground use/exposure to sunlight, or for below ground use/resistance to chemical attack,
2) drainage layout, including provision of manholes, inspection chambers, accessible rodding eyes, traps, pop ups, handhole access, gutters, downpipes, gratings, suitable support and connections,
3) depth and fall of drainage lines,
4) bedding to drainage lines,
5) backfill to drainage lines, and
6) protection to drainage lines (for example, 50mm concrete screed provided where 600mm cover to new drainage was not
achieved), and protection of drains passing through the underbuilding (using lintels or sleeving).
c) Where a public sewer has been built over, or has been connected to, or has been diverted, the person signing this document confirms that Thames Water consent has been sought and obtained.
3) Testing of drainage
Testing is usually in the form of an air test undertaken in accordance with the relevant British Standards. An open test (O/T) is undertaken with the drainage bedded but the trench not backfilled. A final test (F/T) is undertaken on the completed drainage installation, with all sanitary fittings installed. Only where testing is not possible due to the configuration of the existing drainage, a visual inspection of the drainage is undertaken to confirm a satisfactory installation.
4) Guidance on providing drainage layout drawing
Copies of the as-installed drainage layouts are required if you have not built to the approved plans. The following guidance should be used when preparing a drainage drawing:
a) The address and plot number (if relevant) should be added to the drawing.
b) All drainage removals to be indicated by a broken red line and explanatory text.
c) All existing drainage to be shown in black.
d) On all relevant areas of plans and elevations, all newly-installed foul water (FW) drainage to be shown in red and newly-installed
storm water (SW) drainage to be shown in blue.
e) If the drainage differs to the approved building warrant drainage drawings, the size and type of all newly-installed drainage
materials to be fully detailed, to include connections to existing drainage.
f) Show and detail all relevant existing and new drainage (including gutters, downpipes, foul and surface water drainage lines, traps, rodding points/eyes, manholes, inspection chambers, direction of flow, etc.).
g) Each drainage line should be marked with the date of any test and Pass (see note 3).
5) Examples of marking-up drainage layout drawings
