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Architects: Barkow Leibinger
- Area: 6668 m²
- Year: 2013
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Photographs:Zooey Braun , Ina Reinecke
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Manufacturers: Brimat
Text description provided by the architects. Urban Design | Design Concept
The Stadthaus M1 marks the gate to the Vauban quarter of Freiburg – a “green city” partially automobile free, with an emphasis on alternative and sustainable living and architecture. The task of the competition was to design an apartment building complemented by a hotel and shops at the ground level. The construction of wood and concrete is modeled after a ‚passive house’ standard.
This 1st prize winning competition design consists of a separate hotel and apartment building unified by the continuous topography of the roof-scape and facade. The higher and more public hotel is located as an entrance at the main artery of Merzhauser Straße, while the more private apartment building continues behind the hotel along the Vaubanallee. The spatial gap between the two buildings forms a green “pocket park” that opens and widens towards the south, allowing a path between the buildings and a connection to the public circulation and green-room fronting the buildings. This articulation improves daylighting and breaks down the overall building mass on-site.
The low-tech facades save both energy and costs. They are highly insulated in wood construction with 3x insulating panel glazing with integrated retractable louvered sunscreens. The south facades, complimented by loggias and balconies, are additionally protected by climbing plants on steel cables in front of the facade. This layer of planting shades the interiors in the summer while allowing warming sun through in the winter. The north facing facades will be clad in vertical cedar wood-fins, an element that further unifies the two independent buildings visually.
Construction / Building Envelope / Energy Concept
The construction for the hotel and apartment buildings are similar: a passive energy standard is reached by combining a structural concrete skeleton frame (floor slabs, cores, and columns for fire protection) with an insulated prefabricated wood frame infill panel system (non-load bearing). In comparison with a conventional masonry construction this lightweight system uses a fifth more of gray energy. The concrete floor slabs in this hybrid system have the added benefit of providing thermal mass while the thinness of the wood frame walls generates more usable floor area.
The low-tech highly insulated facades are the same for the hotel and the apartment building. The window frames are constructed in Oregon pine combined with passive house standard glazing in the apartments and acoustic glazing in the hotel. Since the hotel is situated at a very busy street, additional noise protection was necessary. The wood exterior cladding is a local white pine stained a light gray. The apartments include exterior louvered retractable sunscreens while the hotel utilizes solar glass.
The south building facades, loggias and balconies at the pocket park between the buildings complement active sun screening with a scrim of climbing/ flowering vines of wisteria and roses. The plants grow rapidly up stainless steel vertical cables held away from the facades. In this way the leafy plants shade the buildings in the summer months while letting in warm sunlight in the cold winter months.
Additional vertical wood fins of Western Red Cedar 20 cm deep on 62.5 cm centers define the remaining northern and end facades. These elements unify the two building volumes further. They read as a continuous form segmented only by the pocket park which separates them into two program types (hotel and apartment).
The roof is standing seam metal with photovoltaic panels laid inbetween.
Energy Concept
One of the most important design goals for the Stadthaus was to realize a sophisticated architectural concept with the energy standards typical for Vauban, in terms of content, technology, and design. In cooperation with Transsolar Energietechnik and Horstmann und Berger Bauphysik, we developed an integral concept that was later executed with Paul + Gampe + Partner.
Hotel and Retail:
The use of a highly insulated façade ensures that the requirements of the German energy conservation regulations EnEV 2009 for the structural heat insulation in the hotel and retail areas were undercut by 15%. The total primary energy supply is 60% below what is permitted. Heating and air conditioning work with the aid of wall-integrated water-bearing capillary tube mats. Partially renewable energy sources are used for heating and water heating, local and long-distance heating. Additional electricity is produced with a photovoltaic plant integrated into the roof.
Housing:
In the residential units, the transmission heat-loss coefficient is 30% below the permissible limit, and the primary energy requirement is 70% below the permissible level. Thus the apartments meet the Freiburg Energy-Efficiency-House Standard 40, based on the internationally used passive house standards. A highly efficient ventilation system with a high heat recovery rate, in combination with a high building density, helps avoid uncontrolled ventilation heat loss.
Program / Organization
The Green City Hotel Vauban has a three-star superior garni standard and is run by a not-for-profit organization as a so-called integration business, where part of the staff has a disability. In this way, the client Freiburger Stadtbau GmbH, which is also a shareholder of the company running the building, combines energy standards with socio-political goals.
On an area of almost 2,800 m2, the hotel provides space for 48 rooms and a suite. To the south, facing the square, the lobby with the reception and a day bar are located, as well as a breakfast room, and a conference area. To the north are the side rooms, the kitchen, and the reception office. On the upper floors, the hotel rooms are oriented along a central hallway to the north and south. Their concept provides for a clear formal vocabulary using sustainable and regional materials. The furniture was made of solid ash wood from the Black Forest.
The residential building contains various apartment types varying in size from 110 to 196 m2, including a maisonette and a penthouse apartment with a generous terrace. Because the plot is oriented in a north-south direction, the central living spaces were planned as a sequence of kitchen, dining and living areas. The two service cores are centrally arranged in the 14-meter deep building block so as to utilize the darker zones. The apartments are arranged around the staircase so that the entire façade can be used for lighting.
Rooms with lower temperatures, where inhabitants spend less time, i.e., bedrooms and bathrooms, are located on the northern façade. Living rooms, children’s rooms and studies are on the southern façade, where passive solar gains can be utilized for heating. Floor-to-ceiling glazing ensures good lighting in the apartments. On the ground floor of the residential building, three retail units for small mixed use businesses contribute to enlivening the square.
