Wohnsinn eG, a co-housing project in Darmstadt

Passive House multi-story apartment complex

While finding my way to the world’s first Passive house, I discovered WohnSinn 1 and its expansion WohnSinn 2, designed by architect Petra Grenz, faktor10 GmbH. This multi-story apartment complex is located very close to where the pioneer Passive house project was completed in 1991, at the urban district of Kranichstein in Darmstadt, Germany.

The first phase of the WohnSinn 1 project was initiated in 2003, a 3860 m² multi-family building comprising 39 apartments, it was judged to be so successful that a second phase of 2,721 m² (living space) building expansion involving 34 apartments was built in 2008 the WohnSinn 2. The concept was developed over a number of years, aiming to  create a diverse yet socially integrated community of households. People with different incomes, ethnicity, backgrounds, levels of physical ability or marital status are living together. Some families purchased their homes others rent them while others rent with welfare assistance from the Government. It would appear that this ‘social experiment’ has been very successful. “As a practical example of the benefits of living in such a neighborhood, it was envisaged that families with young children could call upon their elderly neighbors from time to time to assist with child minding when the need arises.”

Design features

The development consists of a three story south-facing U-shaped layout with some of the units being two story  while others single story. All of the upper  stories are accessible via shared terraces which are connected to a lift at the northeast corner. The entire structure is thus barrier free in terms of access. All of the homes have dual aspects, the two south-north oriented blocks have east and west facades while the connecting east-west oriented blocks have south and north facing facades. All of the ground floor apartments have terraces, many of which have been planted and provide a valuable space.

The corners of the apartment blocks are cleverly used for community purposes, including a day room winter garden and library to the northwest, sauna, guest apartments, a creative room for kids to the northeast and meeting rooms to the southwest. The building is accessible and contain four wheelchair-accessible apartments.

 A landscaped mound in the central courtyard hosts an underground ‘bunker’ room, used by the community to store food and bulky non-perishables that require cool temperatures.

The load-bearing structure consists of prefabricated concrete elements in a cross wall construction. The thermally insulated shell  is made of prefabricated wooden wall elements. The walls have thick cladding of insulation (38cm high density polystyrene) and damp proofing. During construction a rainwater collection was installed with an underground tank for watering the gardens and green roof. The windows where fitted before the external insulation was applied to ensure that an airtight connection between the frame and the shell is achieved. The external insulation was fitted afterwards to cover the window frame thus reducing heat losses through thermal bridging.

Perceived Benefits of the Passive House Standard

The multi-family building of WohnSinn was built to the passive house standard, offering high thermal comfort, healthy indoor air quality, bright living spaces, with low heating cost and a high level of sustainability.

Due to the good insulation and the ventilation system with heat recovery, the heating energy consumption is almost zero. The building losses so little heat that no conventional heating is needed. The living spaces  are mostly heated by passive energy without any boilers/radiators.

Heat input is provided through:

  • large windows
    which allow the warming sunlight to get in,
  • the radiation of body heat of the occupants 
  • the waste heat
    from electrical appliances and from cooking and bathing. Small radiators are running via the hot water supply in bathrooms.

Heat loss is prevented  with the triple glazed windows and doors with triple seals to prevent droughts. Each apartment has a separate ventilation system with heat recovery so that fresh cold outside air can be warmed up to a comfortable temperature by using the heat of the warm stale indoor air as it is extracted (unit recovers over 80% of the heat).

Every household has direct control of their own mechanical system, the control of heating and ventilation is very easy and fairly simple. There are only two adjustable elements: A thermostat for adjusting the need for heating and air exchange rate. There are three levels of air exchange rate; namely low, which is used when the units are left unoccupied during holidays, normal, for everyday use, and high, when there is a need for greater air change rate such as during a party or family gathering. Maintenance is low due to the simple technology: Once a year, two filters have to be washed out and one filter has to be changed. Because WohnSinn is a “single” building and not separate houses heat loss through the walls and roof is considerably reduced.

All residents have the option to invest in the photovoltaic power plant located on the roof of the apartment complex, which provides an annual return on investment of 3 – 4%. Due to the passive house standard and a self-produced power supply via photovoltaic systems on the roof, the energy costs are low.

Selected project details of the WohnSinn apartments:

Architect: Petra Grenz, faktor10 GmbH
Building services: WohnSinn1: Norbert Stärz, Pfungstadt / WohnSinn 2: Hans Baumgartner, Mörlenbach
Principal Construction Contractors: WohnSinn1: Tichelmann & Barillas, Darmstadt WohnSinn2: Büro bauart, Lauterbach, Darmstadt

Treated floor area in PHPP: 3.885 m2 WohnSinn1, 3.097m² WohnSinn2
Construction type: Concrete core made with prefabricated elements with facade comprising a timber frame structure

Annual heating demand (PHPP): 15 kWh/(m²a)
Heating load (PHPP): 10W/m2
Roof: Reinforced concrete slab in 220 mm thickness, 180 mm Polyurethane foam insulation WLG 025, U-value: 0. 135 W/(m2K)
Floor slab: Reinforced concrete slab in 25 cm thickness, underside 300 mm insulation, Thermal Conduction Group 035, U-value: 0.11 W/(m2K)
Walls: 300mm Styropor insulation on concrete elements or 300mm Isofloc in the timber frame elements. U-value: 0.12 W/(m²K)
Windows frames: Fa. Kochs, eCO2, Profile Kömmerling, Thermally insulated plastic frame. Uf = 0.8 W/(m²K)
Glazing: Triple glazing, Ug = 0.6 W/(m²K) g-value = 50%

Air tightness (PHPP):  n50 = 0.35/h
Ventilation: Vallox KWL 90, counter flow heat exchanger. 75% efficient (Manually controlled)
Average air change rate: 0.4/h when occupied 0.25 – 0.3/h when not occupied
Heating installation: water to air heat exchanger connected to a district heating system
Domestic hot water: District heating + 25m² thermal solar collectors (used on WohnSinn2)
Renewable energy production: 250m2 of photovoltaic panels installed in 2009 – productivity not yet determined Jahr 2009