Altbau_Banner final-01

The Altbau, Berlin’s typical turn-of-the-century apartment block, is the focus of our project. Berlin enjoys the biggest stock of pre-war buildings in Europe, yet their biggest attraction — age — makes them huge energy wasters, maintenance often being hampered by complicated ownership situations. Our concept is to create living space on top of the Altbau and to improve its overall energy balance — thus finding one solution to two pressing challenges. The Rooftop House replaces the makeshift inefficient roof truss and gives energy back to the building below.

However, the renovation of the Altbau cannot be a top-down process: it happens in cooperation with the house community. Instead of selling the Rooftop House the way many investment funds sell rare living space in the center of Berlin, we propose a crowd-investment solution. The owners of the Altbau invest to refurbish their rooftop and, optionally, to replace old electrical appliances, remediate windows and façade, and renew the heating system — depending on the particular Altbau situation. Thus the Rooftop House acts as a catalyst to galvanize a local movement encouraging and supporting the owners to bear responsibility for their homes.

GE-310 A3-01


Solo Core




Core Module Altbau fast ohne Linien-01




Being the heart of the house (did we say that before?), the Core integrates all technical appliances, the kitchen and the bathroom while serving as a space defining anchor point – providing great adaptability by allowing the owner to design the free floating space around it. The room layout is only defined through the position of the core module as well as the setting of the movable shelves and bathroom doors (for examples look here).

The incorporation of all basic functions in one core is a very efficient, innovative solution. It is designed as an integral closed part which comes in super handy not only regarding maintenance and reduction of energy losses on the system circuit, but also in terms of transportation and construction: the module can be transported in its entirety and simply be put on top of the base house in one piece. This way we can lower the construction time on site while still maintaining the high quality.


The compact kitchen is located on the southern side of the core module. It does not reveal itself instantly as it is fully integrated into the core module. By using the bamboo material for the surface of the kitchen as well as the module, the kitchen melts into the central unit of our house. Almost every machine (except the oven and the control module of the washing machine) and the entire work space can disappear behind this bamboo skin. Therefore, at first glance, the kitchen has one smooth surface. However, at a second glimpse, the fundamental elements of the kitchen reveal themselves. Concealed behind the cover are storage spaces and more functions such as dishwasher, washer-dryer, freezer and refrigerator. Like the rest of the living area, the kitchen can easily adapt to the owner’s life style. Need more work space? Pull off our removable trim elements and use them as an additional work place. Just place it on the telescopic sub construction between oven and dishwasher or use the mobile roll car to create more operating range. In terms of equipment and material, high quality is essential — especially in technical terms: All of the devices are smart grid compatible!

Kitchen plan

smart grid

/smɑːt  ɡrɪd/, noun

smart grid is a modernized electrical grid that uses analog or digital information and communication technology to gather and act on information, such as information about the behaviors of suppliers and consumers, in an automated fashion to improve the efficiency, reliability, economics, and sustainability of the production and distribution of electricity. In simpler words: The amount of energy won from renewable sources fluctuates more due to variations in production and consumption across the grid. Therefore, the energy has to be stored and used in a smarter way.

© by Wikipedia



The bathroom is also part of the core module and it is anything but ordinary (well, what did you expect?). By opening the central double doors that perfectly fit the profile of the hallway, one doesn’t simply enter a bathroom, but smoothly immerses into the center of the house. Instead of cutting off the room through a conventional small door, we followed our free flowing concept. If one opens the double doors as well as the window and façade elements, the entire room becomes a gateway to the terrace. This way, taking a bath becomes a whole new experience – you are literally bathing in the skyline of this wonderful city.
Verbindung Wasser-01


The Core Module enters a symbiotic relationship with the host building. The connection goes both ways: on one hand the rooftop house’s water is supplied via the Altbau; on the other hand, the electricity generated by our solar panels is transferred to and shared with the host building.

Verbindung Strom-01


The furniture design matches the rest of the house in terms of flexibility and adaptability. Every piece is freely arrangeable, conveniently stackable and some are even extensible. The two shelving structures of the living room and the closet in the bedroom area can be slid along embedded guideways providing a smooth one-directional movement along the room. Thus, they act as defining parameters to the otherwise free floating space that can still be adapted to different situations.


Rooftop Situation Family Dinner


Rooftop Situation DATE


Rooftop Situation Party



Solo Power



Our house is all about energy production and power efficiency. This is achieved by using energy-saving equipment, from LED lighting to insulation material. More importantly though: almost the entire house is covered in photovoltaic modules on both the roof and the façades to ensure that the maximum of the sun’s energy is harnessed and converted to electrical energy. It is designed to cater to most of the house’s energy consumption and to also share its excess energy with the host building.

The PV plants are not – as is often the case – loose add-ons to the existing building but are fully integrated into the architectonic concept. Making the connection between design and engineering possible required a number of innovative solutions and adaptions of common (PV) building standards. However, we believe this aspect is vital in order to raise acceptance towards sustainable forms of energy production in the city. In other words: yes, it is a lot of technical stuff – but damn, it looks good.

Power Banner final-01


The two longer sides of the rectangular house consist of eight glass panels each, four of which are sliding doors. This ensures maximum daylight intake and openness. They are organised in such a way that each living space has access to one of the three different terraces. Each glass panel corresponds to a moveable facade element. The aggregate 14 modules have two parts: the upper part is covered with photovoltaic modules and the lower part consists of a wooden shuttering. When they are open, they become an extension of the roof both inside and outside, following the slight angles of the ceiling.

When the owner is not at home, the automation of the house system adjusts the façade to track the sun to maximize solar power intake. Should the inhabitants be present, they can choose to adjust each façade element in any way they want.

The facade not only reacts according to the course of the sun but also to seasons. Our house opens up in summer, with its widely overhanging roof elements providing shade in daytime while allowing the house to cool at night. In wintertime, the façade elements will mostly be opened in order to maximise passive solar gains, closing only at nighttime. Then the facade elements fold down, creating a preserving shell around the house and thereby insulating it further.



31 Solarsystem-01

Due to the fact that in Germany we have very distinct seasons, energy generation varies greatly from summer to winter. With the more intense sun and the reduced need for heating, production in summer is a lot higher than consumption. In winter though, it is the other way around: consumption exceeds production. As it is not ecological and economical to store the surplus energy from summer until summer, the house is then forced to draw energy from the city’s grid. Due to storage difficulties, it’s nearly impossible to build a house in such a northern region which is completely autarchic throughout the whole year. Nevertheless, over the course of the entire year energy production is 1.3 times higher than consumption, which makes our house an energy plus house.


energy-plus house

/ˈenəʤi plʌhs/noun

An energy-plus house (also called: Plus-Energy House, Efficiency-Plus House) produces more energy from renewable energy sources over the course of a year than it imports from external sources. This is achieved by using a combination of microgeneration technology and low-energy building techniques, such as: passive solar building design, insulation and careful site selection and placement. A reduction of modern conveniences can also contribute to energy savings, however, many energy-plus houses are almost indistinguishable from a traditional home, preferring instead to use highly energy-efficient appliances, fixtures, etc., throughout the house.

© by Wikipedia







The surplus energy generated by the Rooftop Unit is shared with the host building, thus creating a house-intern micro grid. This puts both the owner of the Rooftop House and the residents of the host building in a win-win situation. The owner gets to sell its excess energy for more than the usual compensation paid for electricity fed into the grid, while the price for the local residents is still significantly lower than the standard energy purchase price.




Solo Water


One key point of our concept is viewing the building in its entirety. This implies thinking of its internal functioning processes as closed-loop systems rather than linear systems: energy wastes of some processes become important sources for other processes. The innovative aspect is evident: instead of thinking of a single solution to a single problem, issues are solved with a number of integrated methods, which allow great resource efficiency. Most circuits in our house are designed using this ‘two problems – one solution’ method. Examples are the air-water heat pump that can be used for both heating and cooling or the sewage treatment system that also acts as a part of the cooling system.

Water Banner-01-01


The great innovation, however, is its reversibility which means it is also possible to use the same circuit – and the same working principle – for additional cooling during the hot season. Especially in summer the house is cooled down by using PCM modules installed as a suspended ceiling. They are capable of absorbing and storing heat and releasing it again when the air around them cools down at night.


Our innovative heating and cooling system is essential for generating an ideal climate within the house. The heating demand is met by an Air-Water Heat Pump, which provides us with underfloor heating and backs up the solar thermal domestic warm water supply if required. Instantaneously, an air-water heat pump seemed the most fitting choice since it benefits from the outdoor air thermal energy at a minimum electricity expense. 



Additionally to the airflow, a cooling fluid is running through tubes installed on top of the PCM modules. In case of unexpected heat peaks, the air water heat pump is used to help keeping the fluid cool. However, it is mostly cooled down by leading the tubes of the cooling circuit through a reed bed located on one of the terraces. As the water inside the tubes is warmer than the water in the reed bed, heat convection takes place.

PCM stands for ‘Phase Changing Material’. In our house we use adobe-aluminium-modules filled with material on nano level size that melts or solidifies at a certain temperature (exactly 23 degrees Celsius). Therefore it is capable of storing and releasing large amounts of energy. Heat is absorbed  when the material changes from solid to liquid and vice versa.


The constructed wetland situated outside on one of the terraces serves as both a heat exchanger for the cooling system of the house as well as a sewage purification plant for greywater. Greywater is domestic wastewater from washbasin, shower or bathtub and washing machine. The overall 2 metre wide structure consists of a gravel bedding for filtering of disposal water, and is planted with reed. On one side, the water is applied on top of the reed bed, and is cleaned by dripping through the gravel. A ramp is located over the entire length of the bottom of the casing with a slope of 0.5% to ensure that the water flows steadily but slowly downwards to the exit drainage pipe. The reed is not only a nice green spot on the terrace but also supports the cleaning process. Its roots thrive up to a depth of 1 m and consume nutrients from the water. Furthermore, bacteria settle between the roots and further facilitate the water treatment process. Inside the casing are the gravel and the reed as well as the pipes of the PCM-cooling circuit. The heat that is gathered during the day from the PCM circuit is stored in the gravel and the containing water. Thereby the energy consumption of the cooling circuit is lowered. Simultaneously, heat is delivered to the wetland, which is needed to maintain the cleaning process in lower temperatures. Win-win! The now clean water can then again be reused for irrigation and toilet flushing, for which it will be collected in a container.