They sound alike, they both involve pouring water into a hole, and they are often confused. But a percolation test and a soakaway test answer different questions, and building control will not accept one in place of the other.
| Percolation test | Soakaway test | |
| For | Septic tanks and treatment plants | Rainwater from roofs and drives |
| Method | Building Regs Part H and BS 6297 | BRE Digest 365 |
| Hole | 300mm square, pre-soaked overnight | Trial pit at soakaway depth |
| Result | Vp, seconds per mm | Infiltration rate, m/s |
| Used to | Size a foul drainage field | Size a soakaway |
No. A BRE 365 result cannot be used to design a foul drainage field. That needs a percolation test to Part H and BS 6297.
Often, yes, which saves a return trip. We will plan it with you.
Keep reading
Guide / DrainageHow the test works, what the Vp result means and what counts as a good result for a septic tank.
Read the guide
Guide / HomeownersWhy building control may ask about your ground, and the quickest way to answer them.
Read the guide
Guide / Coal miningWhat it means to build in a Development High Risk Area, and when drilling for old workings is needed.
Read the guideReady when you are
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