Sustainable development includes social and environmental as well as technical aims. In construction, eco-efficiency emphasises the properties of the building, achieved by technical means to fulfil the social and environmental aims. Functionality and adaptability of the interior and indoor comfort are often the key issues for users of a building. Energy and material flows during the use of a building compose a major part of the life cycle energy resource use and environmental pressure. Housing projects ranging from social housing to visions of modern architecture and living in the future were designed and constructed to demonstrate that both user satisfaction and low total environmental pressure can be achieved by building in steel. On the technical level, new innovations of light gauge steel including new structural systems and utilisation of solar energy were demonstrated. It was also shown, that major improvements in environmental properties of a building are possible without much increasing the investment costs. By increased service life of building components, adaptability and functionality of the interior, whole building design for energy and durable structural system and easiness of maintenance and renovation the life cycle costs can be significantly reduced compared to a normal building with the same architectural form and size.