The Musterbauordnung is the model building code set by the federal state and adopted with modification by individual jurisdictions throughout Germany. The code establishes the principle that buildings must generally have two means of egress, however the second egress can be a designated window or balcony for rescue by the fire department. Such rescue is permited with extension ladders reaching up to 8m from grade or with an aerial fire apparatus reaching up to 22m from grade, which is only permitted if the local fire department is equipped with the respective equipment. A second egress is not required if the first egress stair is a “fire safety” stair, which is a pressurized stair core with a protected lobby and standpipe.

In Germany, all buildings over 22m in height are classified as high-rises, subvidived into buildings which are greater than 22m but less than 60m in height and buildings greater than 60m in height. Such high-rise buildings are rarely constructed in cities like Berlin, where planning policies apply a standard height limit of 22m based on the parapet height of the existing city fabric with very few exceptions made. The result is a city of single stair buildings, driven by the legal restrictions of planning and building code policy, and the physical limits of the aerial fire apparatus reach.

Fifth Section
Egress, Openings, Guardrails


(1) For floor areas with at least one occupancy such as dwelling units, offices or independent commercial spaces, there must be at least two independent means of egress per floor; both escape routes can however pass through the same corridor within the floor area.

(2) For occupied floor areas per Sentence 1, that are not on the ground floor, the first means of egress must be a stair. The second means of egress can be another stair or a designated area within the occupied floor area that can be reached by the firefighting apparatus of the fire department. A second means of egress is not required if the first means of egress is a fire separated, fire safety stairwell.

(3) Buildings, for which the second egress requires the fire apparatus of the fire department and in which the sill height of designated windows or landings is more than 8 meters above grade, may only be erected if the local fire department has aerial firefighting apparatus. In the case of special constructions the second egress via fire apparatus is only permitted if there are no concerns regarding occupant rescue.

Diagram borrowed from German ‘Raumpilot’ textbook:

The requirements for exiting are associated with each building classification. The building classes are defined by the model building code (MBO, § 2) and correlating state building regulations. Additional requirements for high-rise buildings with special conditions for exits are defined in the High Building Regulations (MHHR and others).
 

• Buildings up to 7m in height can have a single, unprotected exit stair (building class 3)

• Buildings up to 22m in height can have a single, unprotected exit if the fire department ladder serves as second means of egress (building class 5)

• Buildings up to 60m in height can have a single exit if the stair is a protected “Sicherheitstreppenhaus”

• Buildings exceeding 60m in height must have two exit stairs, one of which must be a protected “Sicherheitstreppenhaus”

Note: building height is measured to the finish floor elevation of the uppermost occupied storey

A Brief History of Housing in Berlin

The building code of Berlin today, particularly with regard to the flexible interpretation of the second egress, is the result of the history of housing in a city defined by dense urban apartment buildings.

“Mietskasernen” (translates to rental barracks) were tenement housing blocks arranged around narrow courtyards, similar in density to Hausmann’s Paris or the Eixample Superblocks in Barcelona, which were critical to housing the growing labor force of the industrial revolutions in the 19th century. The typology was typically arranged as two dwelling units per storey, served by a common stair leading to the narrow courtyard and fire separated from the identical adjacent blocks by masonry fire walls. The dense living conditions were exacerbated by shameless developer speculation and a failure to provide basic sanitary infrastructure. Criticism of these unhygienic and antisocial conditions led to urban renewal efforts after World War II in which architects were invited to propose new designs for the war-ravaged city. At the Interbau 1957 international building exhibition, an entire district of damaged tenement blocks known as the ‘Hansaviertel’ was demolished to make way for new apartment buildings according to modernist designs. Unlike the popularized double-loaded corridor of Le Corbusier’s Unite d’Habitation in Marseille, France (1952) or Mies van der Rohe’s Lafayette Park housing in Downtown Detroit (1959), the designs by Alvar Aalto, Oscar Niemeyer and Walter Gropius for Interbau 1957 were predominantly single stair floor plans.

This brief history of apartment buildings in Berlin is intended to demonstrate the influence of historic and cultural practices and help explain why the building code in Germany allows for single stair buildings up to such height.

Baugemeinschaft Walden 48

Scharabi Architekten + Anne Raupach (2020)
Landsberger Allee 48, 10249 Friedrichshain

Height: 6 storeys incl. mezzanine (18m)
Use: 43 dwelling units
Floor Area: 4,800m²
Construction: Mass Timber
Stair: Reinforced Concrete Walls, CLT Stair
Sprinklered:No

This is the most recently completed of the mass timber buildings on this list, with significantly decreased requirements for encapsulation and the stair and elevator core as a hybrid construction. Each of the stairs serves two or three units per floor for a total of twelve units served by each stair, with an additional eight units on the ground floor.

E3

Kaden Klingbeil Architekten (2008)
Esmarchstrasse 3, 10407 Prenzlauerberg

Height: 7 storeys (22m)
Use: 6 dwelling units, 1 commercial at grade
Floor Area: 987m²
Construction: Encapsulated Mass Timber
Stair: Non-Combustible (Independent load-bearing system)
Sprinklered: No

This early pilot project for mass timber pursued performance-based code compliance to exceed the maximum building height for wood construction. The design provides short travel distances to the exit and distinct fire separation of the concrete exterior stair. Each floor is occupied by a single dwelling unit, accessed from concrete bridgewalks.

"Because the building is comprised of a wooden structure, the escape route had to be constructed in reinforced concrete and set apart from the main building. The open gap gives each apartment a third facade and allows for more flexible interior spaces, thanks to the separation of the stairwell. Moreover, the access via a footbridge is pushed into the urban space and thus emphasized. On three floors, the apartments are accessed via generous, recessed open spaces, which enhances the sense of possessing one’s own floor and home in the city."

Height: 6 storeys (20m)
Use: 39 dwelling units, 1 commercial at grade
Floor Area: 4,420m²
Construction: Non-Combustible
Sprinklering: No

This co-housing project on a narrow urban site is a collaboration between three different architects with distinct floor plans arranged around three distinct stairs within a consistent facade and overall massing . The plan is a typical Berlin block arrangement of shallow, cross-ventilated unit layouts served by a single exit stair. Each stair serves two units per floor and receives natural light either from the facade or from skylights above. Corridor separation is not required, hence each unit opens directly to the stair landing at each floor. The building is of non-combustible construction and divided into three parts by firewalls.

3XGruen

IfuH - Institut für urbanen Holzbau (2011)
Görschstrasse 48, 13187 Berlin-Pankow

Height: 5 storeys (17m)
Use: 13 dwelling units
Floor Area: 2,877m²
Construction: Partially Encapsulated Mass Timber
Stair: Non-Combustible (Insitu Concrete)
Sprinklered: No

The single stair design allows each apartment to take up the full depth of the building, receiving cross-ventilation and daylight from both sides. Although not required by the code, the two storey units in the middle are open to both stairs as appropriate for the collective living of a co-housing project, and accomodating potential future reconfiguration. The street facing balconies also provide the second egress by fire apparatus. The building is a partially encapsulated mass timber structure with the elevator and stair core of non-combustible concrete construction. Sprinklering is not required.

Note: The exit stair includes winders, which are not permitted in Canada (except within or serving a single dwelling unit).

R50

ifau + Jesko Fezer + Heide & von Beckerath (2013)
Ritterstrasse 50, 10969 Kreuzberg

Height: 6 storeys (22m)
Use: 19 dwelling units and shared amenities
Floor Area: 2,780m²
Construction: Reinforced Concrete
Stair: Non-Combustible (Insitu Concrete)
Sprinklered: No

This co-housing project is the result of an intensive consultation and planning process with each of the future residents and resulted in highly flexible floor plans. The orientation of the two to three units per floor around the single stair and elevator enables this flexibility and future rearrangement. The wrap-around balconies provide the second egress by fire department rescue and define the architectural expression of the building. The depth and uninterrupted continuity of the balconies ensure that each dwelling unit can access the street facing elevation for rescue.

IBeB Baugruppe

ifau + Heide & von Beckerath (2018)
Lindenstrasse 90, 10969 Kreuzberg

Height: 6 storeys incl. mezzanine (18m)
Use: 66 dwelling units, 21 commercial
Floor Area: 12,275m²
Construction: Reinforced Concrete
Stair: Non-Combustible (Insitu Concrete)
Sprinklered: No

This long linear block building does have two exit stairs and three double-loaded corridors, but not every dwelling unit has two means of egress. The stacking of maisonette apartments off a single stair from the communal “rue intérieure‘ and the apartments at the ends of the building on every other level are all served by single exit conditions.  The project is very much reminiscient of the stacked corridors and cross-ventilated units in Le Corbusier’s Unite d’Habitation. The building achieves a considerable variation in unit types in part because of the flexibility of the building code in allowing single exit conditions.

“The underlying principle is that units in the centre of the building are arranged in modules over a depth of 23 metres while units at the ends of the building are designed around the cores and establish differentiated interconnections with their surroundings.”