The size and characteristics of dwellings have significant implications for household energy use and greenhouse gas emissions. For example, the amount of floor space affects the amount of energy needed to heat or cool a dwelling. Over a third of separate houses (37%) had four or more bedrooms in 2008 (table 2.8). Building materials used in the dwelling and the amount of insulation installed in roofs, walls and floors, also influence energy consumption. High thermal mass materials such as brick and stone are more energy efficient as they take longer to respond to temperature changes, compared to fibro cement and timber.