The so-called Direct Energy Building of N11 architects and engineers is prototyping a tall house on a small footprint located in Zweisimmen, Bernese Oberland, Switzerland. The owners of N11 combine their office and atelier space in the lower of five stories with a private apartment on the upper floors. Their design approach is about low tech and high brain – designing smart with as little technology as possible, while using natural materials that „breath“ and help to achieve a healthy inner climate.
The whole building has a consequent passive energy design, combining thermal mass of different inertia to buffer extreme temperatures, a highly insulated shell with a solid wooden wall construction, and three-pain windows, where the window surface is larger on the South side than on the North side to allow for a maximum of passive solar gain and a minimum of heat loss.
There is no additional heating or cooling in this house, and no controlled ventilation. The interplay of volume, exposition, slow (concrete, clay) and fast (wood) reacting thermal mass, insulation, window sizes and settings – and of course occupants behaviour – shall, for the given climate on 1400m asl in a Swiss mountain valley, guarantee for a liveable inner climate within a temperature range of 19-25°C.
And indeed, we visited this house on a hazy, grey day with a little snowfall outside, after the sun had not shined for five days. The climate inside was really pleasant, 19°C, naturally bright, a warm feeling and fresh smell from all the visible wood. One could just be there without feeling the need to either find some heat or open the window.
The floors are handmade from compressed clay and coated with a breathable natural wax, providing additional thermal and acoustic mass. The ceilings and upper floors are concrete elements attached to thick-dimensioned wooden beams, forming a thermal mass unit of slowly reacting wood and faster reacting concrete. A ten-centimeter cork insulation and the compressed clay floor are set on top.
There is almost no technology in this house, apart from the necessary minimum of lights and electricity outlets. Cables are all visible and attached onto the walls, protected in thin metal pipes, easy to replace. Radio switches that require no additional cable connection control the lights. The roof’s photovoltaic shingles produce about 2/3 more electricity than needed, which makes this house a plus-energy building – despite of hot water for showers and kitchen being heated by a conventional electrical boiler.
The intended simplicity can be found in many construction details. The load bearing wooden walls are solid, 30cm thick, made from lower quality spruce wood, packed together with wooden dowels from beech hardwood – no glues were needed that could emit harmful substances and prevent from an easy disassembling of the walls after their theoretical end of life. On the outside, there is a six-centimeter thick flax insulation to the solid wood in between a horizontally spaced air gap. The wooden spacers of that gap hold the attached outer facade, which is made from about 4cm thick and 2-8cm deep, vertically aligned stripes from the outer, uneven bark side of sawn timber.
Overall, this wall construction with a theoretical U-value of about 0,15W/m2K is diffusion-open, it regulates moisture and air quality inside to a high extent by the capillary capabilities of the natural materials (wood, clay, flax). No vapour barrier inside and no wind barrier on the outside are needed because of the massive wall from a single material without density barriers. The overlays in the wood wall make it windproof, too. If there is a felt need for fresh air, then windows are opened by hand for a quick air exchange. This saves cash and there is virtually nothing that requires costly maintenance – operating costs are close to zero.
The five-story house was built in five days with the pre-fabricated wall elements and wooden inner walls that need no finishing. Similarly, this building could be disassembled with an easy separation of the few different, mostly natural and mechanically attached materials. This cradle-to-cradle thinking in mimicking nature’s design principles of closed loops and no waste can be clearly seen in the simple and smart building. Congratulations, N11!