Passive House Bulgaria recently announced the winner of its international competition to design a low-energy domicile to be built in Lozen, a village very close to Sofia. The winning entry, from Bulgarian outfit dontDIY, is not only eye-catching, but also fully compliant with the rigorous, though voluntary, Passive house standard.

Buildings that qualify for the accolade of Passive house (it's not limited to residencies) have been described as "ultra-low energy," as they must fall within strict performance criteria per unit area of the building in respect of heating, cooling and energy consumption. This typically results in drastic energy savings when compared to buildings built to meet (though not exceed) national building codes. Oh, and they must leak no more than 0.6 of the house's total volume in air over the course of an hour. Really, the idea is to build a house that requires so little active heating and cooling, that conventional heating and air conditioning systems are not required.

How have dontDIY done it? Well, with a little help from AEE Asian European Engineering, in a number of ways. Perhaps the most eye-catching technology is the 25-sq m (270-sq ft) photovoltaic array destined for the roof (along with a skylights and a garden), generating an estimated (or perhaps I should say calculated) 2380 kWh of electricity per year. But photovoltaics help you to offset your energy demand. Passive houses are really more about reducing that demand through architectural and other non-mechanized design measures - and such measures are far from lacking in this design.

The south facade has a large window in order to maximize solar heat gains (with east and west facades also generously fenestrated), while the north facade is entirely windowless. The overall windows-to-wall area ratio is under 30 percent, yet all the main rooms have south-facing glazing.

And to prevent over-heating during the summer, the south facade has passive stack ventilation built in, so that warm air escapes through high-level vents, while cool air enters through low-level ones. Needless to say, materials have been selected to minimize heat flow between outside and inside.

The house's second floor has been designed as entirely open plan (fret not, the bathroom is downstairs) in order to optimize natural ventilation - the effectiveness of which supposedly receives an additional kick from the choice of location of the house on the available land.

The sloping roof, which lends the design a somewhat jaunty cross-section, is not the result of mere architectural whimsy. These have been carefully measured up in order to achieve optimal facade-to-volume and facade-to-floor area ratios.

A central stairwell forms a quasi-atrium that allows natural light to penetrate right down to the basement-level, where there's another garden.

This may not have any one single eye-catching gimmick that makes this house stand out, but then truly green design is rarely achievable through any one means alone. Here's hoping dontDIY's house works as well in the flesh as it does in paper. Perhaps one day all houses will be built this way, and the very idea of a passive house will be so familiar and ubiquitous as to become meaningless: we'll just call them houses.

See the picture gallery for some of the competition entries the judges thought warranted an honorable mention.

View gallery - 9 images