San Francisco has this week become the latest US city to introduce dramatic new rules on building design intended to slash the city's carbon emissions.

Mayor Gavin Newsom's green building ordinance requires both commercial and residential buildings to conform to strict new building guidelines.

New commercial buildings over 5,000 sq ft must conform to the US Green Building Council's LEED guidelines, while new residential buildings over 75 feet in height must also comply to green building standards, said the Mayor. He hopes that the rules will save 60,000 tonnes of CO2 emissions by 2012, along with 220Gw hours of power and 100 million gallons of drinking water.

Helen Goodland, executive director of the Light House Sustainable Building Centre in Vancouver, British Columbia, dispelled potential fears about increased housing costs as a result of the mandate.

Developers considering performance metrics when pricing projects would find no cost increases, she argued. "We find that the cost increment argument is put out by those that are worried about being put at a perceived market disadvantage and/or do not want to shift from business as usual," she said. "So, lots of different numbers are floated around. It is safe to say that the greater the price increment, the more indication the developer, builder or designer doesn't know what he/she's doing."

In related news, British Columbia's Climate Action Team also proposed strict green guidelines for new building developments last week. Recommended measures included reducing greenhouse gas emissions from all new public buildings to zero by 2016, following with all new commercial buildings by 2020. This would require buildings to buy clean energy or generate their own.

The team also recommended updating British Columbia’s new Green Building code every three years. The code currently requires homes to meet the EnerGuide 77 standard, and mandates ASHRAE 90.1 - a North American energy efficiency standard - for larger developments.

The new green building guidelines follow hot-on-the-heels of the launch of a similar green building code in Los Angeles. Meanwhile, across the Atlantic the UK government is set to introduce new rules ensuring all new homes are "zero carbon" by 2016 and all new commercial buildings meet the same "zero carbon" standards by 2019.