Gas and hydrocarbon membranes in Warwickshire

Where the gas comes from

Old mine workings and shafts in the north of the county can release mine gas, with methane and carbon dioxide the usual concern. Former sand and gravel pits along the Tame and the Avon were often backfilled with waste, which can generate landfill gas. In Rugby, Nuneaton and the market towns, old engineering works, depots and filling stations leave hydrocarbons in the ground. Radon is assessed separately, and the ground investigation states whether it applies.

The consultant's BS 8485 assessment turns all of that into a protection level and a specification. We install to it.

From one plot to a whole phase

Our Warwickshire gas work ranges widely. A single replacement dwelling on a coalfield village plot needs the same care with its laps and service entries as a large phase of housing on the edge of Nuneaton or a distribution shed on the A5. What changes is the planning: on a housing phase we follow the slab programme plot by plot so the membrane goes down as each base is ready.

Big sheds bring long, open runs of membrane, which are quick, and then clusters of column bases and drainage gullies, which are not. We plan the crew for both, and agree with the site team which bays are released first so the steel erectors and the slab pour are never waiting on us.

Laps, collars and records

First we look at the surface we will be laying on. If there are sharp stones, loose rubble or anything else that would pierce the sheet, it gets put right before we begin. Laps are formed by whichever method the product's maker prescribes, welded on some systems and sealed on others. Each pile cap, soil stack and duct receives its own collar and seal. Rushed laps on a wet day and sloppy service entries cause most failures we come across, so neither is hurried.

• Coalfield, landfill and hydrocarbon protection
• Substrate inspected before laying
• Individual collars at every penetration
• Integrity testing and third-party validation available
• Records for the warranty provider

Proving it before the slab is poured

A third-party verifier can check the laid barrier, test it and issue a certificate. For coalfield and landfill plots in the county that is increasingly a warranty requirement. We can set it up, along with integrity testing, and either way our own laying records are handed to you for the warranty file.

On a housing phase, validation visits are usually booked plot by plot, and we programme the laying so each plot is ready for its inspector before the concrete gang arrives.