With the launch of a new building code – CALGreenon January 1 this year – California has taken a major step toward greater sustainability. It now has the greenest building standard of any state in the country (green building codes have previously been adopted by US cities, but this is the first to be taken up statewide). And crucially, it is mandatory. Now that California has taken the plunge, will other states follow and institute similar compulsory codes? Can California’s example help to drive greener building practices abroad?

For new buildings constructed in the state, CALGreen requires a number of sustainability measures. Included in the code is a mandatory reduction in water consumption -- 20% below the requirement in the previous California Buildings Standards Code -- as well as the use of low pollutant-emitting paint, carpets, floorings and other materials. It also requires that 50% of construction waste be diverted from landfill and energy-system inspections be conducted by local officials to ensure heating, ventilating and air-conditioning systems meet efficiency standards.

With buildings accounting for 40% of energy consumption in the United States, and the building materials industry a further 12%, officials in California are looking to their new code to help the state meet its goal of cutting greenhouse-gas emissions to below 1990 levels by 2020  – and by 80% below 1990 levels by 2050. The code is also expected to reduce construction waste bound for landfill, currently estimated at 2.5 to four tonnes for an average home.

CALGreen is similar in scope to LEED – the world’s best known green building rating tool – but there is a crucial difference. While LEED is a voluntary performance standard that awards certificates for good practice, California’s new system is compulsory: green standards are actually written into the state’s building code. “The impact of CALGreen is huge,” says Walker Wells, architect and green urbanism programme director at environmental NGO Global Green USA. “It makes official all of these things that were once exotic…It says green has become part and parcel of the way buildings are designed and built in the state of California, and it’s setting a precedent for the nation.”