To take full advantage of the sun's warmth and light, the house is oriented due south. A full-width conservatory on the south side provides free space heating on sunny days in the cold season. In the height of summer overheating is prevented by the conservatory blinds and closing of the internal doors to the conservatory. Many east and west facing windows enable optimal use of natural light. Minimal north facing and no south facing windows prevent excessive heat loss or gain. Two storage rooms on the north side function as "extra insulation".
Building materials are as much as possible renewable and/or recycled.
The walls and roof are insulated to a thickness of 25cm using Warmcell, which is made of recycled newspaper. A 20cm layer of Celotex (polyurethane) insulation material was placed underneath the 10cm concrete floor slab. The windows are double low-E glazed.
No central heating is required for space heating due to the high standard of insulation and the passive solar heating. Instead, a high efficiency wood stove in the living room supplies heat during the coldest four months of the year, and whole house ventilation with heat recovery circulates air through the house all the time. It also pulls in fresh outside air and pre-heates this with the heat from the moist air expelled from bathrooms and kitchen. That way the house benefits from a constant supply of pre-heated fresh air with a heat loss of max. 10%.
An air source heat pump situated in the utility room uses the warm space air to heat the domestic hot water.
The roof is pitched at an optimal angle for highest solar yield. Over time, as panels got less expensive and feed in tariffs more generous, we went from 1 kWp of photovoltaic cells during building, to 4 kWp in 2012, and finally 7.5 kWp in 2018. This more than covers the electricity we need, even with a plug-in electric car.
Three Growatt SP2000 batteries with a total capacity of 15 kWh were installed in 2018 as well, to make better use of the electricity we produce. This also enables us to charge the electric car overnight on electricity produced during the day.
For cooking we use an induction hob, which is powered by the photovoltaics just like every other electrical appliance in the house.
We also prepared for a roof-mounted wind turbine, but haven’t found a satisfactory model so far.
A 5000 liter rainwater tank was installed with the aim to supply rainwater for the toilets, washing machine and the outdoor tap. At the time (in 2001) these systems were still in their infancy, and the electronics failed in a particularly rainy year. We now use this rainwater to keep the vegetable garden, green house, wildlife pond, and houseplants alive in the increasingly long periods of drought.
Low flush toilets and thermostatic taps further help cut down on water usage.
The garden includes wildlife areas and a kitchen garden, both designed to HDRA's organic guidelines
Through our work we also strive to contribute. Laurence's Engineering Doctorate thesis provides a method to calculate the optimum mix of renewable generation technologies in each individual setting, so that urban properties can be as close to zero carbon as possible. He also provided the energy consultancy on the Steijger Solar House, resulting in all of the above.