Soakaway Design and Installation

A soakaway disposes of surface water by infiltration into the ground. Sizing depends on drained area, rainfall design basis, and proven percolation — not a generic crate count copied from another plot.

This page covers installation briefing for UK sites. Design and percolation testing are specialist inputs; Mainline installs to the approved detail. Large development attenuation and adoption strategy belong on attenuation and drainage-adoption flagships, not on this domestic/plot soakaway guide.

review Groundworks Contractors in Wandsworth and Groundworks Contractors in Kingston.

When this drainage work is specified

When Building Control or the designer requires on-plot infiltration; when replacing a failed soakaway; or when connecting gullies and roof drainage to a new crate or rubble chamber.

What installation typically includes

Typical construction excavates to the designed plan size and depth, places a geotextile-lined crate system or specified granular fill, connects inlet pipework, and backfills with care so the structure is not crushed.

Location rules (distance from buildings, boundaries, and water sources) come from the design and local practice — do not invent a universal UK offset from this page.

Where infiltration is unsuitable, the designer may specify attenuated discharge instead; that is a different system.

If this matches your project stage, send drawings and site details for a scoped quote — or call to talk through programme and access constraints.

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Construction sequence

Step 1: Confirm design and tests
What this step delivers: Size and location approved.
Step 2: Excavate and form
What this step delivers: Chamber to design geometry.
Step 3: Connect and backfill
What this step delivers: Inlets live; structure protected.
Step 4: Record as-built
What this step delivers: Position and invert noted.

Common failure points and constraints

Percolation test completed for the design
Crate or rubble soakaway on drawings
Roof and gully connections shown
Building Control expecting infiltration evidence
High water table or clay making infiltration doubtful

Pre-install and testing checklist

Soakaway drawing and percolation results
Service check in excavation zone
Inlet pipe falls from drained areas
Geotextile / crate specification
Maintenance access if required

Coordination with structure and adoption

Install to detail, protect from silt during construction, and leave access for future maintenance where specified. Record as-built position for the property file.

What drives complexity on site

Dig volume, disposal, crate specification, and restricted access drive cost. Failed percolation late in the job forces redesign. See soakaway cost under /groundworks-costs.

Frequently asked questions

Can Mainline size my soakaway without a percolation test?

No. Sizing needs design inputs including infiltration performance. We install to the engineer’s detail.

Is a soakaway the same as attenuation?

No. Soakaways infiltrate; attenuation stores and controls discharge. See attenuation systems for developers for development-scale storage.

How This Issue Is Normally Diagnosed and Repaired

Follow the typical path from problem identification through to resolution:

We provide these services across the UK, including

London Richmond Chiswick Wimbledon Fulham Hammersmith Ealing

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Have a soakaway detail and percolation results? Request an installation quote.

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Related Services

Groundworks Contractors

Full-service groundworks for commercial and residential construction.

Excavation Contractors

Bulk excavation, strip excavation and trenching for construction.