Car park lining in Solihull

Permeable paving on mudstone

Permeable paving lets rain straight through the surface into a deep stone sub-base. On free-draining ground the water can carry on into the soil. Most of Solihull is mudstone, which won't accept it fast enough, so the sub-base has to hold the water instead and let it out slowly to the drainage.

That turns the car park into storage. A welded membrane under the stone keeps the water in, stops it softening the clay formation, and sends it to the outlet at the rate the engineer has set for the Blythe or the Cole. The 2025 national SuDS standards push designers towards this kind of surface-level storage, so we expect to see more of it.

Our share of the build

Digging and trimming belong to the groundworker. When the formation is ready we walk it before unloading anything, looking for level, sharp stones and a clear fall towards each outlet. A non-woven fleece goes down first and is turned up the sides, then the membrane is unrolled in panels and every joint is fused with hot-wedge or extrusion welders. One trial weld is made and logged before production welding starts.

Each outlet, overflow and service crossing is sealed into the sheet, and the sheet is carried up the perimeter to the height on the drawing. A second fleece then covers the membrane, and the groundworker brings in the stone and the paving over it.

• Formation walked and accepted first
• Fleece under the membrane and over it
• LLDPE, HDPE or PP, joined by welding
• Outlets and crossings sealed through the sheet
• Weld log in the handover pack

Town centre, airport and business parks

The sites differ more than the method. Around the town centre, car parks are tight and hemmed in by buildings, and deliveries have to be timed around shoppers. Near the airport and the NEC the areas are larger and flatter, and the lining can run for days in long continuous strips. On the business parks off the M42, the car park is often one part of a bigger SuDS layout, with swales and tanks downstream of it.

Working round a live site

Plenty of Solihull car park jobs are extensions or rebuilds on sites that stay open: a business park adding spaces, a hotel resurfacing, a retail unit reworking its frontage. The groundworker usually phases the dig bay by bay, and we line each phase as it is handed to us, so the cars can come back as soon as possible.

Some layouts need more storage than the stone can give, and the engineer adds crates underneath. We install those too, and the lining and the tank share a single set of records.