House in Hegenlohe
In addition to the client’s own residence, which has a living area of 290m2, the house contains a 35m2 self-contained flat. Situated in a new development area in the Mittlerer Schurwald nature reserve, the structure is surrounded by buildings with traditional double-pitched roofs. One of the constraints imposed by the local authority development plan was that the present house should have the same kind of roof as its neighbours, with a pitch of between 20° and 35° and a red clay-tile covering. To ensure that the proposed energy supply is met entirely from regenerable sources, 66 photovoltaic modules – matched to the dimensional grid on which the building is based – were assembled, raised somewhat above the layer of tiles. This proved to be the simplest and most economical means of installing the plant and sealing the roof. The dimensions of the photovoltaic elements and the area required for them (120m2) were determined on the basis of calculations of the electrical needs of the house. To obtain the necessary surface area for the elements, an asymmetric double-pitched roof was built with a large, south-west-facing slope inclined at an angle of 18°. The electricity generated by the photovoltaic installation is not used directly in the house, however. It is fed in its entirety into the public grid in accordance with a law on renewable forms of energy, which in this case foresees a reimbursement of ?0.452 per kilowatt hour. In other words, the installation meets the electrical needs of the house formally – but not directly – by means of an annual balance. The solar energy required for the building is first fed into the electricity grid. To optimize the efficiency of the heat pump, two 99-metre bores were driven into the earth. The highly insulated outer skin of the house in conjunction with its compact layout (area : volume = 0.58) results in specific thermal heating needs of approximately 40kWh/m2a. The solid mass of the concrete walls, together with the suspended gallery slab, which also functions as a thermal-storage volume, serves to reduce peak temperatures and helps to ensure pleasant indoor conditions in summer.