How Much Land Drain Do I Need?
Quick Answer
Measure total trench length + 10% for junctions
Standard 80mm or 100mm perforated pipe. A 25m herringbone system typically needs ~55m of pipe
How We Calculated This
Land drain quantity depends on your drainage layout:
- Single run: Trench length + 10% = total pipe needed
- Herringbone pattern: Main run + branch runs (typically 3–5m spacing between branches)
- Perimeter drain: Building perimeter + run to outfall
Pipe Sizes
- 60mm: Light garden drainage
- 80mm: Standard domestic land drain
- 100mm: Heavy-duty or long runs
- 160mm: Main collector drains
Trench Specification
- Width: 300–450mm
- Depth: 600–900mm minimum
- Fall: 1 in 100 minimum (1cm per metre)
- Backfill: 20mm clean gravel surrounding pipe
- Geotextile membrane to prevent silting
Materials Per 10m of Drain
- Pipe: 11m (10m + 10%)
- Gravel (20mm clean): ~1.2 tonnes (300mm trench, 150mm gravel bed + surround)
- Geotextile membrane: ~6m²
Last updated: April 2026