There is a growing movement to build ecological housing with extremely low purchased energy consumption for heating and cooling, and minimal CO2 emissions. Two examples are: "Factor-Four Plus Housing" requiring one-fourth or less of the purchased heating energy of houses built to current standards and "Passive Houses". Such houses typically require a maximum of 10 W per m2 of space heating, amounting to an annual energy demand of 15 kWh/m2 in temperate climates (central Europe).

Until now such housing achieved this high performance primarily by reducing heat losses, i.e. compact building form, thick insulation and ventilation heat recovery. While the number of such buildings is growing, market penetration would be enhanced by a complimentary approach; namely in very well insulated housing increasing energy gains. This can be achieved by:

• passive solar design,
• active solar systems for domestic hot water and space heating,
• PV electric supply systems,
• improved daylighting (for improved living quality) and
• natural cooling and solar/glare control.

Task 28/38 will address cost optimization of the mix of concepts reducing energy losses, increasing useable solar gains and efficiently providing backup in order to achieve the same high performance. This comprehensive approach has the potential to increase market penetration through greater architectural freedom, improved living quality, owner pride in using renewable energy, and acceptable total costs. To adapt the solar houses to a larger part of the housing market, studies of the national trends and the governmental goals for the housing industry will be carried out.