The Curse of the Double Egress
- Conrad Speckert
- Feb 18, 2023
Illustration by Bjoern Arthurs
THE FLOOR PLANS of apartment buildings in Canada are typically designed with a layout known as the “double-loaded corridor”: an arrangement of residential units on both sides of a long hallway, usually with two exit stairs near the opposite ends. Although a double-loaded corridor is more efficient than a “single-loaded” corridor (with units on only one side of the hallway), neither is commonly used for small apartment buildings outside North America. This prevalence of double-loaded corridors is the result of the strict building code requirement for two means of egress (i.e., two exits). In Canada, the code requires two means of egress for any multi-unit residential building of more than two storeys, subjecting a three-storey apartment building to the same requirement for two exit stairs as buildings of 13 or 30 storeys. This is a significant design constraint and carries a cost to the quality of life in low-to mid-rise apartment buildings. Double-loaded-corridor designs are inherently bad at providing every dwelling with access to sufficient daylight and natural ventilation. Units on one side of the building are exposed to much more traffic and noise—and in buildings with a north-south orientation, units on one side get too much sun while units on the other don’t get enough. Combine this with a structural grid of concrete shear walls determined by the most efficient arrangement of underground parking spaces, and the result is repetitive, narrow, single-orientation units with mostly one or two bedrooms. Larger, more family friendly apartments with three or four bedrooms are only feasible on the outside corners of the building. This (along with the unfavourable economics of larger units as a measure of per-square-foot returns) contributes to an oversupply of small units and a corresponding shortage of units suitable for larger households in urban areas—thus moderating the demographics of these buildings and the neighbourhoods where they are located. These layouts are so ubiquitous in North America as to seem inevitable—a standard way of constructing multi-unit residential buildings. However, this arrangement is highly uncommon and rarely seen in other countries, outside of hotels and dormitories. Instead of having a dozen or more apartments accessed from a long corridor between two exit stairs, building codes outside Canada and the US allow for buildings (up to a certain height) with one exit stair, with strict limits on the maximum floor area, occupant load, and/or number of apartments it serves. The urbanism of European cities such as Berlin, Barcelona, and Paris is defined by entire city blocks that are subdivided into multiple single-stair apartment buildings. Instead of two stairs connected by a long corridor serving a dozen or more units, a single central stairwell can serve a few apartments on each floor (and can be repeated side by side depending on the size of site). Sweden’s building code, as an example, allows for one exit in residential buildings up to 16 storeys, with a maximum occupancy of 50 people per storey. The entry doors into each of the apartments in a single-stair building also require higher fire ratings and smoke-tightness standards: 60 minutes of fire resistance, versus a 20-minute rating in Canada. Compared to a building with two exit stairs connected by a double-loaded corridor, the Swedish rules see far fewer people sharing an exit and provide much better protection against the spread of fire and smoke from the unit of fire origin. These other building codes and built forms are much less restrictive than the rules in Canada, and I would suggest also provide superior fire safety to our requirements.
ALLOWING SINGLE-EXIT CONDITIONS would make it easier to construct small apartment buildings and avoid the continued default to double-loaded corridors in mid-rise housing. Canadian and American architects generally consider the double-loaded corridor to be the most efficient and cost-effective way to arrange a floor plan, yielding around 85% sellable or leasable floor areas. This efficiency target is important early in the design process to estimate whether a project will generate a sufficient return, and developers often request design changes until this goal is met. While 85% efficiency is usually achievable with two exits on larger properties, small infill sites cannot accommodate the depth of a double-loaded corridor floor plan and achieve this target. As a result, these properties may sit vacant for years, remaining undeveloped until adjacent properties can be assembled into a larger site. Small single-stair buildings can handily outperform larger double-loaded-corridor buildings and generate efficiencies over 90%. Permitting single exits would also make it easier to construct larger units in these buildings. Restricting single-stair buildings to a maximum of four units per storey incentivizes maximizing the size of each apartment to get the most out of each floor. Single-exit buildings would facilitate an increase in housing that can accommodate families—something that is in desperately short supply in urban areas. My graduate research compared international building codes, examining the maximum building heights allowed with a single exit stair. This was the first step toward proposing a code change to permit single-stair buildings taller than two storeys in Canada. Of the 30 jurisdictions I reviewed, Canada is the most restrictive. The United States is slightly more permissive, allowing one exit for apartment buildings up to three storeys if an automatic sprinkler system is provided. Australia and New Zealand allow for one exit stair in unsprinklered buildings up to 10 metres (three storeys) and in sprinklered residential buildings up to 25 metres (eight storeys). Spain requires two exit stairs for apartment buildings above 28 metres in height, Austria above 32 metres, Denmark above 45 metres, France above 50 metres, and Germany requires two exit stairs for apartment buildings above 60 metres (about 20 storeys). Even Japan—a country known for having restrictive building codes to address its considerable earthquake risk—permits apartment buildings of up to five storeys with one exit stair. The UK, Switzerland, and South Korea do not set a maximum building height for single-exit residential buildings at all, placing restrictions only on the maximum floor area, number of dwelling units, and/or occupancy load of each storey.
THE FIRST EDITION of the National Building Code of Canada (NBC), published in 1941, permitted buildings of up to three storeys to have a single exit; this was later lowered to two storeys, with stricter limits on occupant load and floor areas. This was based on the US code, which “originated from the local codes that existed in New York, Philadelphia, Boston, Chicago and Baltimore,” according to a 2015 report on the history of our regulations. “These were all cities in which large conflagrations had occurred, accelerating the development of local building regulations.” Canada and the US share a history of combustible wood-frame construction, whereas non-combustible masonry and concrete construction are more prevalent in Europe and Asia. It stands to reason that the North American code requirement for two means of egress was a trade-off for permitting cheap, fast, and easy-to-build wood-frame construction. The BC Office of Housing and Construction Standards and the Canadian Wood Council have published detailed reports on the historical origins and rationale for the floor area and height limits on combustible construction in the NBC, and while the reports do not directly address the issue of exiting, they demonstrate that much of the building code is based on fire-safety assumptions from the early 1900s: The basis for the height and area limitations in the 2006 BCBC [British Columbia Building Code] were developed nearly 100 years ago when city conflagration or large life loss were prominent considerations. The means for dealing with these risks, in part, was to limit the height and area of buildings to what the fire department of the time could reasonably handle. The statistical fire record has shown that the number of fires is decreasing, loss of life in fires has decreased, and the relationship of city-wide conflagrations to interior building design is not correlated in a reasonable way to building height and area. In summary, there is a lack of definition to correlate the building area and height to the overall construction, compartmentation, and fire and life safety systems. This suggests that the requirement for two means of egress in any building over two storeys is also the result of fire-safety practices in combustible construction from more than 100 years ago. At the time, methods of construction were much less controlled and fire separation within buildings was less regulated: the interior of residential buildings included more wood finishes and gypsum drywall was not as predominant of a material; automatic sprinkler systems, smoke detectors, and fire-alarm systems were in their infancy; and fire departments were not equipped with the aerial ladder trucks, breathing apparatus, and other modern communication and rescue equipment that exist today. Building codes in many other jurisdictions are also simply more recent documents than ours are, drafted as nations rebuilt after the Second World War. The origins of the Canadian and US building codes date from before the war, and hence many outdated fire-safety assumptions remain with us.
THIS IS SPECULATIVE, but I also suspect that because Canada does not have a long history or strong culture of dense urban living, our building code and zoning bylaws have not been optimized to support this kind of growth. Consider the enduring problem of exclusionary zoning bylaws in North American cities: rules that forbid other types of housing in single-detached neighbourhoods. One example of this is the outright ban on apartment buildings Toronto imposed in 1912, which persists to this day in the form of “yellowbelt” single-detached residential zoning. For much of the 20th century, suburban ideals dominated the housing narrative across North America and municipal zoning bylaws were deliberately written to encourage sprawl and prohibit denser forms of housing. The blanket requirement for two means of egress compounds this issue and makes it difficult to build multiplex and small walk-up apartment buildings, even if zoning regulations are changed to allow for them. Consider the very peculiar quirk of the Canadian code that allows single-stair conditions in a three-storey building if that stair is contained within one dwelling unit and opens directly to the exterior at grade but that requires two separate exit stairs in three-storey buildings with stacked apartments, regardless of whether the building is sprinklered or the walls and door into the stair are fire rated. This has the effect of making three-storey townhouse developments very efficient to build and making “missing middle” three-storey walk-ups significantly more expensive, even though the height and scale of these buildings are the same. An exception in North America, Montreal offers an alternative history of medium-density housing enabled by the city’s distinct interpretation of the requirement for two means of egress. Along with Saint John, Winnipeg, Vancouver, and Lloydminster, Montreal is one of the few chartered cities in Canada with the power to draft municipal bylaws that contravene provincial and federal regulations. The “Montreal triplex” is a form of missing-middle housing made possible by these powers: it consists of three stacked dwelling units that share a curved exterior staircase on the front and a spiral stair at the rear of the building. The National Building Code requires any curved or spiral stair that serves more than one dwelling unit to have “an inside radius that is not less than twice the stair width,” which translates to such stairs being so inefficient as a measure of floor area that they are only used for monumental and processional spaces like a theatre or grand entrance. However, Article 29 of Montreal bylaw 11-018 includes an exception to the National Building Code to allow for tight-radius spiral stairs as a shared means of egress for two dwelling units per storey in buildings of up to three storeys. The economy of scale that results from this exception to the building code is one of the reasons why Montreal’s density and mix of housing options is so distinct within Canada. Modern infill projects, like the ingenious Les Quatres Arbres at 4878 Avenue Henri-Julien, are feasible precisely because of this particular code exception. Anywhere else in Canada—including in Laval and Brossard, directly adjacent to Montreal—such designs are not permitted, and municipalities do not have the legal authority to create an exemption from the provincial building codes that prohibit them. Much like Montreal and its unique spiral-stairs exception, many US cities have local codes that are distinct from the state building code and the misleadingly named International Building Code (the model building code that each US state adopts, with modifications). New York City and Seattle have their own building codes that allow for single exits in apartment buildings of up to six storeys in many circumstances. According to Seattle’s building officials, this provision was added in 1977 and “the driver for these code changes was that development happening at the time was being constrained by building code requirements. There were many small lots being developed and two exits took up a significant portion of the floor plate.” Capitol Hill Urban Cohousing in Seattle is an excellent example of what that city allows on a small urban infill site—in this case, measuring 40 feet wide by 113 feet deep (roughly the dimensions of a typical postwar suburban lot). The project’s architect, Mike Mariano (who also lives and works in the building), told me that a design with two stairs would have reduced the number of apartments from nine to six and would have precluded affordable co-housing. His drawing of the stair also beautifully illustrates the spatial relationship of the single exit, which overlooks the courtyard, to the light and air each apartment gets from both sides.
THE CONDITIONS LAID OUT in the 2018 Seattle Building Code lay the groundwork for the proposal to allow single-stair buildings of up to six storeys in the National Building Code. The height limit is based, among other things, on providing sufficient hose-stream penetration with the standard 75 foot (22 metre) aerial apparatus of a typical North American fire department. Although Seattle isn’t as permissive as some other jurisdictions, such as the UK (no limit) or Germany (60 metres), Canada and Seattle share a common history of combustible construction and suburban sprawl and both the National Building Code of Canada and Seattle Building Code originated from rules developed in the United States in the early 1900s. In a 2004 interview with the Toronto Star, renowned architect Eb Zeidler described the shortcomings of the City’s planning policy of encouraging mid-rise buildings along major streets because of onerous minimum parking requirements and the building-code requirement for two means of egress. Those parking minimums have since been eliminated, and the City of Toronto is currently reviewing zoning regulations to “expand opportunities for ‘missing middle’ housing forms in Toronto” and allow “more residential units in forms compatible with existing houses, such as duplexes and triplexes, where they are currently not permitted.” Should zoning regulations change to permit more of this missing-middle housing, the building-code requirement for two exit stairs will remain a significant obstacle to building it. In 2019, the Ontario Association of Architects Housing Affordability Task Group published a report looking at how to urgently increase housing supply and make it financially attainable. “In addition to revising current municipal land use regulations and zoning permissions,” the report found, “the Ontario Building Code should be revised to remove regulatory hurdles in order to reduce construction costs—example: create an alternative means of achieving Ontario Building Code compliance to permit a 4-storey building with a single exit.” This January, a group of 45 prominent architects, planners, developers, and housing-policy experts co-signed my letter to the Ontario Housing Affordability Task Force recommending a building-code change to permit residential buildings of up to six storeys with a single exit stair. Two months later, Ontario’s minister of municipal affairs and housing announced a new piece of legislation titled More Homes for Everyone. It included changing the Ontario Building Code to “facilitate more infill and low-rise multi-unit housing by exploring opportunities to allow for single means of egress in four to six storey residential buildings, while continuing to protect public health and safety.” The architecture critic for the Globe and Mail wrote that this “sounds boring, but would open up enormous possibilities for small and midsized buildings in our cities. Small infill is a crucial part of providing more housing, and more diverse cities.”
Conrad Speckert is an intern architect; his graduate research on means of egress in multi-unit residential buildings has since evolved into a CMHC-funded project to amend the National Building Code of Canada.