House XS is sustainably designed in terms of size and investment values, as well as in absolute energy consumption and provides pleasant living. It has good orientation, allowing passive heating in winter and preventing overheating in summer. It has a wooden, energy-efficient, load-bearing structure and wood wool insulation. All windows and doors are also made of wood. The building is heated with a heat pump, and occasionally with a fireplace. The house is ventilated by a heat recovery system. The rainwater that collects in the reservoir is used for flushing toilets, car washing and garden needs.