While covering America’s broken architecture and construction industries recently, I made a passing remark on how single stair buildings should be legal. This resulted in several comments and discussions across a spectrum of media. It is a topic I weighed in on regularly for several years, but I had never seen this much consternation regarding it.
Simply put: Single stair buildings can be a good thing.
However, I first want to acknowledge the horrific tragedy of London’s Grenfell Tower. About its only similarity to European buildings is that the 24-story tower had a single stairwell. It was designed to compartmentalize fires that occurred, but as the recent trial has laid bare, it was poorly managed and badly renovated, with an incredible number of faulty decisions leading up to the fire.
Acknowledging this tragedy is important because I am not advocating that construction should be a free-for-all — in fact, far from it. Building regulations are necessary for establishing minimum standards, safety, and accessibility. Often they are data-driven, but there are also cultural elements based on historic practices found in building regulations.
In the United States, building and energy regulations are written by a private entity rather than government agencies, as found in Europe, Canada, and most other countries. It should be noted single stair multifamily buildings are incredibly common in Europe and most don’t have fire sprinklers either. That goes for both existing, historic, and new construction. The tallest single stair building I’ve seen outside of the United Kingdom, in comparison, is only 10 floors.
Europe is laden with pre-war single-stair buildings — such as Gaudi’s Casa Calvet in Barcelona, Spain — because this was how dense urban housing was built to accommodate the massive influx of workers migrating to cities, before the advent of the elevator and when people got around primarily by foot. In these urban centers, building parcels were generally narrow and family-owned – and they were expanded on over time. Due to the narrowness, there was largely only room for one stairwell.
Most of the construction wasn’t wood framed like in the United States, but rather solid construction — generally brick or stone, and eventually concrete. Floors and roofs/inhabited attics were built with wood beams and floors. Thus, many buildings were of the sort where vertical elements were relatively fire-resistant, but the horizontal elements were not.
There was no professional fire brigade until the 19th century. With little to no fire regulations, cities throughout Europe had massive fires. Some, like Passau, Germany, had multiple fire events that destroyed the city several times over.
Construction detailing and the onset of concrete floors generally changed the equation on this, allowing for compartmentalization to slow or contain fires. Mass Timber today can be designed to operate in a similar manner.
To this date, the single stair configuration has endured. But double-loaded corridor buildings — buildings with units on either side of a central hallway — have been less common. I don’t know the exact reasons for this, but I believe a large part is cultural. Double loaded corridors prevent units from getting lights from multiple sides, and they don’t allow cross ventilation, which is a growing issue on a warming planet. (Yes, even for multifamily passivhaus projects.)
Double loaded corridors generally have dark hallways, and result in less usable space per floor than a single stair configuration, especially if your building code allows units to enter directly off the stairwell, as they do in Germany, Austria, and France. There are also structural tradeoffs with a double-loaded corridor, particularly for a building that is cellular or repetitive in design like a hotel, dormitory, or efficiency units. Single stair buildings generally have more flexibility in their floor plan configurations.
Another issue with large double-loaded corridor buildings is there are more people using the same elevators, halls, and entries. There are more people entering this sort of building than would in a single-stair configuration, due to limits on the number of units per floor. There are certainly social implications for this worth evaluating, whether one is more personal or impersonal. Post-pandemic, does it make sense to design buildings where many residents are using the same public spaces or does it make sense to partition buildings into smaller pods?
So, what does this single stair configuration look like in Germany or Austria? Well, for starters, it should also be noted there generally is not a requirement for sprinklers. There are regulations on fire-rated stairwells, walls, and floors. There are limits on the number of units per floor for each stair – four for Germany; eight for Austria. There are maximum travel distances to the stairwell (115 feet).
There are limits on the building height as well: In Germany, the floor must be a maximum of 72 feet above grade — generally seven or eight stories. Interestingly, 72 feet is the max wall height for most of the Berlin Altstadt, which was set at the max height of ladder rescue, as well as street width in case of collapse. There are allowances to go a little higher with more stringent requirements on exit doors and egress, as well as the availability of rescue apparatuses that can reach this high. This is where it gets interesting.
Austrian architecture firm Querkraft Architekten designed an incredible 8-floor passivhaus multifamily building with a single stair configuration serving up to eight units per floor, in the heart of Vienna, Austria. Note the exterior (thermally broken!) concrete balconies. What is the function of balconies? The function of balconies is to access urban life, the outdoors directly from one’s unit. However, most importantly, it is the second means of egress.
Yes, you read that correctly. Like the United States and Canada, German and Austrian building regulations require two means of egress. The difference is that, in part due to compartmentalization, their regulations allow the second means of egress to be the fire brigade rescuing residents – even without sprinklers in the building. How do they do this? For one, they have monstrous fire apparatuses that can do bucket rescues on tall buildings such as this rescue in Karlsruhe at 131 feet up.
In Germany, there are also very specific regulations on fire planning — where buildings are located, separation between buildings or courtyards, the heights/widths to get around or through a building to a courtyard, as well as where apparatuses go to make these rescues. When I was working there, a fair amount of my time was spent planning for stuff like this, studying schleppkurven (turning radii) and apparatus layouts. Perhaps it is also a function of smaller, more nimble fire apparatuses in Europe. Possible also, is their fire departments spend more time dealing with fires, rather than medical emergencies, as in the United States.
Germany also allows for multiple single-stair configurations to be used in the same building, as in the lovely walden48 baugruppe by scharabi + raupach architekten, a massive mass timber multifamily development that is effectively broken up into 3 separate buildings, separated by firewalls. Similarly, the Dennewitz Einz baugruppe — one big development, 3 separate buildings, designed in collaboration by 3 separate architecture firms. These units get light on multiple sides, cross-ventilation, and a good variety in the unit mix. Those additional measures for additional height that I mentioned are how a 10-floor, mass timber multifamily building with a single stair, like the Skaio in Heilbronn, Germany, by Berlin-based architecture firm Kaden + Lager, can be built.
Another personal favorite is this 9-unit, 7-floor social housing project by FRES architectes in Paris – a stunning project that would be infeasible if a second stairwell were required. As well as this 6-floor plus mezzanine and roof deck multifamily building by Lola Domènech and Lussi + Partner in the heart of Barcelona.
Mexico and Japan also have 10-story, single exit buildings. Despite this abundance of buildings with single stair configurations and little to no active fire suppression, these buildings are quite safe due to compartmentalization and building regulations. Many also have wonderful, daylit, open stairwells for active usage by residents.
Per this FEMA report, France, Germany, and Austria all have much lower fire death rates than the United States, where multiple stairs and active fire suppression are required for most multifamily buildings. Despite what we have been led to believe over the years, single stair multifamily buildings are legal even in some U.S. jurisdictions. The International Building Code allows for up to four floors, but with stringent regulations including a max of four units per floor, and requirements for sprinklers. Seattle allows up to six floors plus a mezzanine with a single stair configuration.
Personally, I think it is amazing that these kinds of buildings are possible. Many are the smaller, fine-grained urbanisms that make for great cities we talk about so often. They can be family-friendly, with a diversity of unit types, and are both space and energy-efficient. They are also accessible, as buildings in both continents require elevators on projects like this and many in Germany are barrier-free or adaptable.
Most importantly, they are legal. Maybe we should follow suit.
