Part H · England · Free to use
Drainage field area calculator
Floor area of a drainage field for a septic tank from the percolation test result.
Approved Document H (2015)
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s/mm
Part H · Result
50 m² drainage field
At = p × Vp × 0.25 = 5 × 40 × 0.25
Checks passed- Percolation value: Checks passed12 to 100 s/mm40 s/mm
- Floor area of field: Calculated resultAt = p × Vp × 0.2550 m²
- Vp: time in seconds for the water to drop from 75% to 25% full, divided by 150; at least three tests in two holes (paras 1.34 to 1.37).
- Package treatment plants use BS 6297 (reference only).
Clauses this relies on
Source edition and scope
Approved Document H (2015).
This is a preliminary check of the conditions shown. Confirm the edition, project circumstances and any additional requirements with your architect or building control.
A design aid, not legal advice. Checked against the Building Regulations 2010 for England; confirm with building control.