Completed in 2010, the Velux Sunlighthouse claims to be the first zero energy and carbon neutral house in chilly Austria. The design was generated as a full-throated effort to squeeze as much energy out of the sun year round. But the sustainable planning did not stop there. The design took great care in implementing very low embedded energy building materials, which in turn gave way to a super efficient shell and an elegant natural interior. The difficult lot on which the home was designed for made the feat all the more impressive, as Hein-Troy Architects squeezed a stellar solar energy system into use, while maintaining a very bright and livable home. The Velux is the first house in Austria with a measurable net environmental footprint.
The home’s long skinny lot, with partial shading and awkward orientation prevented the architects from achieving the aggressive Passivhaus standards. Instead they maximized the solar potential as well as the efficiency. The large sloping roof maximizes solar exposure hosting three technologies, which make full use of the sun. The first is a grid of skylights that provide passive solar and maximize daylighting throughout the space. Rows of solar thermal panels set between the skylights heat domestic water and assist in space heating. Finally a 48 square meter solar array provides 1/3 more electricity than the home consumes.
The mechanical system is focused on a brine water ground-source heat pump for the underfloor heat and hot water needs. Passive cooling is achieved during the warmer months with an elegant design that uses an open stairway and the stack effect. Windows automatically open and the energy recovery ventilator shuts off in accordance to the room temperature, making the system work with little intervention by the occupants.
The material selection carefully considers the use of low-impact and low-embodied energy products. The walkout lower floor required a lot of concrete, so the decision was to use Slagstar, which replaces the majority of the cement with industrial slag, eliminating nearly 90% of its CO2 footprint. The rest of the structure is built largely using locally sourced pine finishes, wooden structural elements and cellulose insulation to reduce both production and transportation energy. The building has been estimated to offset all of its carbon emission after 30 years of occupation, making it the first true carbon neutral home in Austria.
Photographs © Adam Mørk