The International Energy Agency's Task 13 is to advance solar building technologies. As part of that programme, 15 houses in 12 countries have been built to test new technologies and strategies for achieving low energy demand while maintaining a good indoor climate.;The principal strategies used and evaluated are: minimization of heat losses, profiting from passive solar and internal gains, heating with an active solar system, heating with recovered heat and providing auxiliary heat efficiently.;For each house, this work provides a list of energy features incorporated, an analysis of energy demand, a floor plan, and a description of methods of construction. The houses range from apartment blocks to detached and terraced housing. Local weather conditions, building styles and cultural requirements are taken into consideration.