Architecture firm Studio Apxe has completed a new house that will generate more energy than it uses. As well as high efficiency, the house, in Kladnica, Bulgaria, features biomass heating and solar panels on its roof to generate electricity.

Studio Apxe cites sustainable development and energy efficiency as its main design focuses. Coupled with these, the aim of this project was to build a large, one-story house in a green landscape without it appearing too conspicuous.

The 970 sq m (10,441 sq ft) building is comprised of lightweight steel and timber structures, with concrete used sparingly. The construction used local materials where possible, such as stone and timber. The main living areas sit above the garage, which is dug into the rock at street level. Colder service spaces, such as the garage, are kept separate from the living spaces so as to minimize heat loss.

A variety of architectural measures were taken to ensure the house was kept as efficient as possible. Keeping glazed areas out of the shade, triple glazed windows and super-insulation of the building are all contributory factors. Indoor air quality is managed by a mechanical ventilation system with heat recovery.

The efficiency of the house is also contributed to by excellent levels of air tightness. According to Studio Apxe, hundreds of details in the house were designed with air tightness in mind. The target was to reach a level of 0.6 air changes per hour at 50 pascals pressure, the level required for Passive House accreditation. The Kladnica house reached levels of 0.13 and 0.19 air changes per hour across two tests.

The house's biomass heating helps to keep energy requirements down to 38 kWh per square meter annually, well below the 120 kWh per square meter figure needed to be counted as a "passive house," the international standard for high energy efficiency that was developed in Germany during the 1990s.

The costs expended on achieving the passive house standard came to 5.93 percent of the overall construction costs. The further investment to reach "energy plus" levels were a further 9.24 percent of the overall costs.

Energy needs, such as for lighting and household appliances, are met by an array of 50 12.25 kWp photovoltaic panels installed on the roof with an annual yield of 10,750 kWh. This represents 52 kWh per square meter of energy generated on an annual basis, putting the house 14 kWh per square meter in the black each year. Meanwhile, 12 solar collection units heat the swimming pool in summer and feed into the heating system during the winter. The electricity generated is stored in batteries with any surplus transferred to grid.

The house took just under a year and a half to complete with an estimated final production cost of €953 (US$1,301) per square meter, something that Apxe views as an achievement to be proud of, given the materials and systems used.

Silvia Draganova, one of the project architects, told Gizmag, "We believe that buildings in the future should be more comfortable, providing joy and healthy indoor environment to the residents. This can be achieved only through the most advanced international environmental standards."

Source: Studio Apxe