Gas membrane installation in Nottingham

The coalfield on the city's doorstep

The Nottinghamshire coalfield wraps around the west and north of the city. Colliery sites at places like Gedling, Calverton, Cotgrave and Hucknall have since become housing estates and country parks, and the old workings and spoil beneath them can give off methane and carbon dioxide.

Where the ground investigation picks that up, the consultant sets a protection level, typically using the BS 8485 approach, and names the barrier and how it must be detailed. We lay exactly that product, with each lap welded or sealed the way its maker sets out.

Brownfield inside the city

Closer in, the hazard comes from what industry left behind: rail yards, gasworks, lace and engineering works, and old sand and gravel pits along the Trent that were later filled. Hydrocarbon contamination is common on former depots and filling stations. Each brings its own gas or vapour regime, and the membrane class follows it. Radon can also feature in parts of the county, and the risk assessment will say if it applies.

Every pile cap is its own job

Poor ground in the coalfield often means piles, and piles mean a slab peppered with penetrations. Every one of those, plus drainage pipes, ducts and columns, is wrapped in a purpose-made collar and sealed separately. Gas protection tends to fail at a rushed detail long before it fails in the middle of a sheet.

We check the blinding or slab before we lay. Sharp stone or reinforcement ends can puncture the barrier, and we'll flag it before the first roll is opened. Laps aren't made in rain or on wet surfaces; if the weather turns, we stop and pick up again when it clears.

Proving it before the slab is poured

While the barrier is still exposed, integrity testing and an independent validator's inspection can both be booked. Each plot's installation record is then sent on for the warranty provider and building control, so a phased estate builds up its file as it goes.

On a typical Nottingham estate that means a short visit per block of plots rather than one long stay, timed so the slab gang isn't kept waiting for us and the concrete pour stays on its booked date.