Which test should I use?
The drainage assessment tool will help you identify which test needs to be carried out. Smaller low risk developments, which have an increase in impermeable area less than 25 m², can use the Building regulations Part H test. This a much smaller test pit, which can be hand-dug and only needs a bucket of water to test.
For all other developments the BRE DG 365 2016 should be used (Further details below).
The key requirements for the test are:
- Size has to be representative of the use and actual depth (typically 0.6 m wide x 1.5 m long and 1.2 m deep)
- Three complete tests in succession
- Each test must fully drain to empty (No partial drains)
- If the test pit doesn't fully drain, due to time constraints, then the infiltration rate must be calculated from the tested depth and the 25% and 75% depths adjusted accordingly.
- The slowest rate must be used for the final result - do not average the results.