Gas membrane installation in the West Midlands

Why so many West Midlands plots need gas protection

The Black Country and much of Birmingham were built on coal, iron and heavy engineering, and parts of Staffordshire and Warwickshire sit over old coalfields. Redeveloping that land means building on made ground, old mine workings, filled-in canal arms and former landfill, all of which can give off methane and carbon dioxide.

Former garages, depots and works add hydrocarbon contamination to the list. On sites like these the ground investigation will usually end with a gas risk assessment, and the planning conditions and warranty provider will expect the protection it calls for.

The specification comes from the ground investigation

Under BS 8485, gas monitoring on site gives a gas screening value, and that puts the site into a characteristic situation from CS1 to CS6. From CS2 upwards the building needs protection, scored as a combination of the floor slab, ventilation beneath it and a gas-resistant membrane. Your consultant does the monitoring, the assessment and the design.

We install the membrane to that specification. Where hydrocarbons are present, the membrane has to be rated for them, since not every gas membrane resists hydrocarbons.

Radon is assessed separately from methane and carbon dioxide, but the installation discipline is the same: a continuous barrier across the footprint, sealed at every lap and every service entry. The design states which gases the membrane has to resist, and we install a product rated for all of them.

Where gas protection lives or dies

Most failures come from penetrations that were never sealed properly and laps made in bad conditions. Our process treats each of those as its own job:

• The slab or blinding is inspected before we lay, and we say so if it would puncture the membrane.
• Joints are welded or sealed to the manufacturer's method, with no shortcuts at the laps.
• Every pile, service and structural penetration is collared and sealed individually.
• Integrity testing and independent third-party validation are available.
• Installation records are provided for building control and the warranty file.

Fitting in with the build programme

The membrane goes in between the groundworks and the slab pour, so it sits on the critical path. We sequence with your groundworker and concrete gang, and where validation is specified the inspector checks the installation before anything covers it. Coming from Tamworth, we are close to most Black Country and Birmingham sites, which helps when a pour date moves.

Housing plots, schools, commercial units and industrial sheds all need the same care at the details. A terrace of houses means many service entries and plot-by-plot sequencing; a warehouse slab means long runs of membrane and a large number of pile caps. We plan the crew and the materials to suit.