Construction of new buildings on gas-contaminated land.

Incidents involving landfill gas in buildings have increased in recent years and these are of concern to developers and builders who are faced with the problem of developing sites where this gas is present. The principal components of landfill gas are methane (which is flammable) and carbon dioxide (which is toxic), but these two gases are also associated with coal strata, river silt, sewage and peat. Approved Document C of the Building Regulations has been revised to take account of the problems that landfill gas poses to building development and this report is intended to supplement the information contained in that Approved Document. The report provides a brief background on the production of landfill gas, its properties and how it migrates offsite. It then goes on to discuss assessment of gas-contaminated sites and outlines the construction principles that need to be followed when ground where methane and carbon dioxide are present is built on. The types of construction covered in this report are a concrete slab with a granular venting layer, and a ventilated subfloor void. It is recommended that private houses should be protected using only passive measures, and that active measures, which include gas monitoring, are only appropriate where there is a responsible body which can provide continuing maintenance for these measures. The report gives minimum recommended areas of ventilation and the standard for gas-proof membranes. It also recommends that service pipes and cables should be directed into buildings above the floor but that if this is unavoidable then all entry points should be properly sealed against gas ingress. Guidance on the construction of buildings on landfills that are actively producing gas is not given in this report; in these instances further specific guidance should be sought.