Gas membrane installation in Coventry

Why Coventry sites end up with a gas risk assessment

Old factory sites around the city are being turned into housing, student blocks and new employment space. Their ground can hold made ground, fuel and oil residues from workshops and depots, and backfilled pits. Towards Keresley, Exhall and Bedworth the old mine workings add the possibility of mine gas. Former landfill and gravel pits along the river valleys bring methane and carbon dioxide into the picture.

Your consultant assesses the gas risk under BS 8485 and sets the protection level. Ours is the installation: the right membrane, laid and detailed the way the specification and the manufacturer require.

Under the slab, before anything else

We start with the surface. Blinding or the slab beneath must be clean, with nothing standing proud that might pierce the sheet, and if it isn't ready we tell the site manager before laying a metre.

On a terrace of Coventry plots, the sheet runs from one base to the next and its laps are joined as the product's instructions say: some types are welded, others sealed with the maker's own tape or strip. On a former works it is more often one large slab with ground beams, lift pits and drainage crossing it, and each change of level needs its own fold and seal.

Penetrations decide the result

Gas finds the weak point. Every pile cap, soil pipe, duct and incoming service gets a collar and seal of its own, and we treat each one as a separate detail rather than a gap to patch at the end. On a piled block with dozens of penetrations, that is where most of our time goes.

Hydrocarbon-resistant grades matter on the old garage and depot plots, because a standard barrier can soften in contact with fuel residues. The specification names the grade; we make sure what arrives on site matches it before we start.

• Radon, methane, carbon dioxide and hydrocarbon barriers
• Laps joined as the product's instructions require
• Collared seals at every pile, service and duct
• Integrity testing and independent validation available
• Our records supplied for the warranty provider

Validation and the warranty file

On riskier Coventry plots, a growing number of warranty providers want a third party to look at the barrier and test it before concrete goes on. We can book that inspection, and we leave every collar and lap visible for it. Whether or not one is booked, the client receives our own laying records for the file.