Soakaway installation in Solihull

When the borough's ground will take water

Mercia Mudstone underlies most of the borough, and a trial pit dug into it tends to fill and stay full. The exceptions are the valleys of the Blythe and the Cole, where rivers and ice left behind patches of sand and gravel. On those patches an infiltration test can pass comfortably.

The patches are irregular. A plot in Hampton-in-Arden can drain well while the field next door holds water like a bowl, so nobody should assume a result from a neighbouring site. The design follows the tests taken on your plot, and we build to that design.

Garden plots, drives and village infill

A lot of Solihull soakaway work is small: a replacement house in Knowle, an extension in Dorridge, a pair of new homes on a large garden in Hockley Heath. Under Approved Document H, infiltration is the first option to try for surface water, so building control will expect a soakaway wherever the tests support one.

Small plots bring tight access. Crates are light and stack well, so where a lorry can't reach the hole we bring them in on a smaller vehicle and carry them through. Neighbours, parked cars and finished landscaping are part of the job, and we leave the drive as we found it.

Inside the crate structure

The groundworker opens the pit to the size and depth on the drawing. We look at the base first: it needs to be level and firm, with no loose spoil or standing water. The permeable geotextile is spread out next, and we build the crates up within it until the design volume is reached. The inlet is then connected through the catchpit or silt trap the engineer has specified.

Once the connections are made we fold the geotextile over the top with generous overlaps, so no fines can find a way into the crates. The structure is then ready for backfill, which the groundworker places.

• Crates and geotextile supplied, or installed from your own stock
• Inlet and silt management connections as drawn
• Wrap closed and inspected before backfill
• Inspection record and handover note for building control

Where we'd advise against it

River gravels can carry groundwater close to the surface in wet months, and a soakaway sitting in it stops working when it is needed most. If the results look marginal, or the separation to groundwater looks thin, we will tell you before the crates go in. Your engineer will then usually move to a lined attenuation tank with a restricted outfall, a system we build as well.