Gas membrane installation in Bradford

Iron, wool and shallow coal

South of the centre, Low Moor and Bowling were ironmaking districts, and the Coal Measures there and around Wyke and Tong were worked from shallow pits. Old workings like those may give off methane and carbon dioxide. In the valleys, mill sites carry their own history: boiler houses, fuel oil tanks, dye works and yards built up with ash and cinders.

None of that makes every Bradford site a gas site. The ground investigation and gas risk assessment decide, usually with BS 8485 as the basis, and the protection level they set is what we build to.

New build and mill conversion

Housing on cleared mill and works land usually gets a membrane across the whole ground-floor slab. Conversions of the big stone mills are different work: new floor slabs laid inside old walls, with the barrier carried up and sealed against masonry, columns and lift pits. Ground-floor flats in a converted mill often sit on a new slab cast over old cellars packed with rubble, and that fill is exactly what the investigation looks at.

In both, we inspect the surface we are laying onto first. Sharp aggregate, steel offcuts or a ridge of concrete will damage a barrier, and we raise it on the day if the surface isn't ready.

Laps and collars

Each lap is welded or sealed exactly as that product's instructions say. Then the slow part:

• A collar at each service entry, soil pipe and duct
• Each pile cap and column base detailed to the drawings
• Junctions with existing walls sealed as the specification describes
• Any damage from following trades repaired and noted

Proof for the warranty file

Integrity testing and independent validation by a third-party inspector can be arranged, and they are worth having on a complex slab with many penetrations. Installation records are handed over in a form the warranty provider and building control can check against the specification.

In an old mill the hardest details are often the ones nobody drew: a cast-iron column on a stone pad, a culvert under the floor, a flue base. We flag those early so the designer can say how they should be sealed before we reach them.

New-build estates on the old pit and ironworks land to the south are simpler in shape but larger in area. There the challenge is keeping long runs of open sheet clean and intact while bricklayers and drainage gangs work around it, so we lay and inspect in plots, matching the build sequence.