The Coal Measures under south and east Leeds were mined for centuries, much of it at shallow depth, and abandoned workings can let mine gas, methane and carbon dioxide, migrate upwards. Add the flax mills, engineering works and railway yards of Holbeck, Hunslet and the Aire valley, plus old tips and filled ground, and a lot of sites carry made ground or contamination.
Regeneration on the South Bank and along the river is putting new homes and offices on exactly that land. Whether a building needs protection, and how much, is settled by the ground report and the risk assessment built on it.
We start by inspecting the slab or blinding. If there are sharp edges, loose aggregate or standing water, we flag it and wait for it to be put right.
Each joint is welded or sealed, whichever the manufacturer's specification calls for on that product. Where hydrocarbons are part of the risk, the membrane is chosen to resist them, and the barrier we fit is the class on the drawing.
On a piled city-centre slab there can be a great many pile caps, and each one is collared and sealed individually. Service ducts, drainage, lift pits and slab steps get the same treatment.
Gas protection rarely fails across an open stretch of membrane. It fails at the corners and the collars, which is where our time on site goes. A slab with dozens of piles and a run of service entries along one wall can take longer to detail than to cover, and we price and programme it on that basis.
Leeds city-centre plots are often boxed in by streets, adjoining buildings and buried services, with little room to store rolls or turn a delivery. We agree laydown space and delivery times with the site before we arrive, and lay in areas as the frame contractor releases them.
A lap made on a wet, dirty slab is a weak lap. On a raw Leeds morning that can mean drying the work area or waiting for the weather to lift before we join anything.
Integrity testing and validation by an independent third party are available, and warranty providers often ask for them on higher-risk Leeds sites. BS 8485 is the standard designers use to set the protection, and at handover you receive the installation records your warranty provider will file.
