The Velux Sunlighthouse is the first CO2-neutral family house in Austria with an above-average portion of daylight. Two southwest-facing roofs which are equipped with 43 m² of monocrystalline photovoltaic panels and 8 m² of solar panels, a geothermal heat pump and the direct solar energy yields of the windows, will generate more energy in 30 years than the amount of energy that was necessary for constructing, transporting and running the house. This project shows that - even in Austria where difficult terrains occur quite frequently - it is possible to build houses without an ecological footprint.