The Code for Sustainable Homes is the standard by which new homes in England, Wales and Northern Ireland are now being judged for their green credentials. The Code covers a wide range of environmental issues: energy and carbon dioxide emissions, water usage, materials, surface water run-off, waste (site and household), pollution, health and well-being, site management, ecology and land use. Homes are assessed at the design stage and post construction. Each dwelling has its own assessment, and if it meets the required criteria, then it is awarded a certificate, ranging from Level 1 to Level 6, depending on performance. This guide looks primarily at how to achieve Levels 3 and 4 as these were in 2009 the levels most commonly specified.