A low-energy house is characterized by an energy-efficient design and technical features which enable it to provide high living standards and comfort with low energy consumption and carbon emissions. Traditional heating and active cooling systems are absent, or their use is secondary. Low-energy buildings may be viewed as examples of sustainable architecture. Low-energy houses often have active and passive solar building design and components, which reduce the house's energy consumption and minimally impact the resident's lifestyle. Throughout the world, companies and non-profit organizations provide guidelines and issue certifications to guarantee the energy performance of buildings and their processes and materials. Certifications include passive house, BBC - Bâtiment Basse Consommation - Effinergie (France), zero-carbon house (UK), and Minergie (Switzerland). During the 1970s, experimental initiatives for low-energy buildings were made in Denmark, the United States, Sweden, Canada, and Germany. The German Passivhaus Institute introduced the first passive house in 1990. The implementation of standardized low-energy building concepts has developed differently in each country. Buildings alone are responsible for 38% of all human GHG emissions (20% residential, 18% commercial) as of 2008. According to the Intergovernmental Panel on Climate Change (IPCC), buildings is the sector which presents the most cost effective opportunities for GHG reductions. Interest in low-energy buildings has increased in the United States, primarily due to rising energy prices, decreasing costs for onsite renewable-energy systems, and increasing concern about climate change. California requires all new residential construction to be zero net energy by 2020. Triggered in the 1970s by the first energy crisis and growing environmental awareness, energy conservation became increasingly important in Germany. In 1977, the country's first energy-related building standard was enacted.