Rigorously enforced stringent building codes can cost effectively achieve energy savings, reduce energy bills and curb greenhouse gas emissions. This paper combines on-site data from some 800 dwellings, energy use information, survey data and computer simulations to evaluate the impact of the most recent energy efficiency provisions of the British Columbia Building Code on residential energy use in British Columbia, Canada. Key findings are as follows:

• First, the estimated compliance rate of 0.63 is in the mid-range of estimates for similar codes.
• Second, for natural gas heated single family dwellings and duplexes, the estimated gross unit savings were 4.5 GJ per year, while for natural gas heated row houses and apartments, the estimated gross unit savings were 2.5 GJ per year.
• Third, for natural gas heated single family dwellings and duplexes, total net savings were 24.0 TJ per year, while for natural gas heated row houses and apartments, total net savings were 7.6 TJ per year.
• Fourth, for electrically heated single family dwellings and duplexes, the estimated gross unit savings were 820 kWh per year, while for electrically heated row houses and apartments, the estimated gross unit savings were 380 kWh per year.
• Fifth, for electrically heated single family dwellings and duplexes, total net savings were 1.5 GWh per year, while for electrically heated row houses and apartments, total net savings were 2.1 GWh per year.

In conclusion, two conditions must be met if residential building codes are to have a significant impact on residential energy consumption. First, the requirements of the building code must be materially more stringent than existing building practice. Building codes which essentially reflect current building practice may weed out a limited number of poorly designed or constructed buildings and level the playing field for all market actors, but they are not likely to save very much energy. Second, achieving high levels of compliance with the code is essential. Compliance can be potentially increased by a combination of building code training and education for market actors and code enforcement activities targeted at areas of suspected noncompliance.