Small Lots and the Case for Single Stair Reform

A step towards more, family friendly housing

Before we get started today, a plug for two upcoming events:

1. Join a bunch of allied housing organizations on Thursday April 30th at 5:30 at the iO Theater for for ‘Tax & the City,’ a community conversation designed to answer one very important question: Can a land value tax revitalize reinvestment in Chicagoland?

2. Come hang out with other City That Works readers next month, Wednesday, May 13th at Midwest Coast Brewing from 5:30-7:30pm. We’ll be joined by local Alderman Walter “Red” Burnett, who’s been fighting for more housing in the 27th Ward. Sign-up here to let us know you’re coming.

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Zak Yudhishthu writes and researches about housing and urban economics, including on his Substack Pencilling Out, where this article is cross-posted. Alex Montero is the chairperson of Strong Towns Chicago, an all volunteer advocacy group focused on housing, street safety, and transit.

In recent years, Chicago has made meaningful reforms to its zoning code that make it legal to build more homes in more places. That work isn’t done. But as our zoning improves, we also need to reform our building code, to ensure that the new homes allowed on paper can also be built in practice.

One of the most important changes to pursue is single stair reform. It’s a proven change to enable neighborhood-scale infill housing with more family-friendly apartments and condos. City Hall should pass a single-stair ordinance that applies best practices from peer American cities, like Seattle and Austin, to re-enable the type of neighborhood-scale development that made Chicago the vibrant city that it is today.

The New Bottleneck

Two parts of Chicago’s Municipal Code dictate the housing that’s legal to build in our city. These are the zoning code, which is the main character of housing advocacy discourse, and the building code — its less famous but quietly powerful older cousin.

The zoning code (Title 17) regulates building size and use. It defines zoning districts that dictate how tall buildings can be, how much of their lot they can cover, how many housing units are allowed, and how much parking they must provide. The zoning code also contains the city’s zoning map (Official Zoning Atlas), which assigns every lot in the city to a zoning district.

The building code (Title 14) regulates building design and construction. It includes minimum standards for construction materials, electrical, plumbing, HVAC, fireproofing, and emergency exits. Just as the zoning code governs what can be built, the building code governs how it can be built.

Chicago has taken important steps to reform its zoning to unlock new housing since 2020. Revisions to the zoning code through the Connected Communities Ordinance and ADU Ordinance have made it easier to build more housing units and less land-hungry parking in certain zoning districts. Map changes including the Broadway Upzoning, Western Upzoning, and Missing Middle Housing Initiative have rezoned city lots to less restrictive districts. All this is good for building more homes for Chicago’s households and growing the city’s tax base.

As zoning codes improve, the building code becomes an increasingly important bottleneck to building new housing on small lots. There are now single and double lots in Chicago, many vacant or underused, where zoning allows for the construction of a 7-24 unit building by right — but the building code, and especially Chicago’s stringent two exit stairway requirement, makes this functionally impossible.¹

Why Two Staircases

In Chicago, homes in buildings taller than two stories are required to have access to two exit stairways. This requirement is stricter than all other large US cities, where a single stairway is allowed for buildings up to at least three floors.²

The intended benefit of requiring two exit stairways is simple: in the event of a fire, two staircases provide redundancy so that residents have a clear path of escape no matter which part of the building the fire starts in. In larger buildings, two stairways also allow firefighters to use one staircase to move hoses and gear into the building to fight the fire while evacuating residents through the other stairway.

This standard creates predictability in an emergency and allows residents and firefighters to act quickly when every second counts. Typically, buildings provide access to two staircases by running a hallway through the center of the building, with stairwells on either side. This creates the “double loaded corridor” layout common in hotels and most modern apartment complexes.

Narrow Lots and Tricky Geometry

The problem is that this standard makes it much harder to build the sort of family-sized housing stock that is in high demand across Chicago. Chicago’s standard lot size is unusually narrow: 25 feet wide by 125 feet deep across most of the city’s urban grid. This small size gave rise to traditional naturally affordable two, three, and four-flats, as well as humble storefronts along commercial corridors with apartments above.

To maximize light and reduce dead space, Chicago’s narrow lot multifamily buildings have large windows in living spaces like frunchrooms and kitchens in the front and rear. Smaller windows face gangways or light wells on the sides for bedrooms and bathrooms. Long corridors are mostly absent in these buildings because they reduce access to light along the exterior walls and compete with living areas for precious square footage.

Typical layout for narrow-lot apartments in Chicago. Image credit: Wurlington Press

Even with the constraints of a narrow lot, a typical building has more than enough square footage for a unit in the front and a unit in the rear on a single lot.³

Image credit: Aggregate Studio's Flex Flat concept

But since at least 1903, newly built housing more than two-stories tall must give every unit access to two stairways. To comply with this requirement, narrow-lot buildings with this unit layout must include two stairways connected by a corridor on every floor, or three stairways across the front, back, and middle. This leads to the absurd situation where a three story six unit building on a single lot has more stairways than a high rise with several hundred units.

This thorny constraint has haunted small lot development in Chicago for a long time. In the past, neighborhood builders addressed this challenge with retractable metal fire escapes, or back porches with exterior stairs. But our current code bans the retractable fire escapes for new construction. And exterior porches are only legal in buildings up to four stories high, while facing more rules than they did in the past.⁴

Historic single lot mixed use building with side fire escape for egress in Little Village. Image: Alex Montero.

This creates two problems. First, all those staircases take up space that could otherwise be used for housing. With less square footage per unit, the resulting units are likely to be cramped and have less light. This also pushes development towards more studio or one-bedroom units, and fewer family-sized apartments.

Worse, two-staircase requirements make it functionally or financially impossible to build as many units as the zoning code allows. Instead, developers have to build fewer units, or they must assemble multiple lots to build a larger apartment, which is a limiting and costly additional step in development. Absent those options, nothing gets built at all, and rents continue to rise.

Single Stair Buildings Enable More Housing

A recent report by Pew attempted to directly estimate the construction cost of a second staircase. Based on a hypothetical five-story, 14-unit apartment on a small lot in New Jersey — similar to the small apartments typical in Chicago neighborhoods — they estimated that a second staircase could represent 6-13% of hard costs for a new building. Loosening the requirement for a second staircase would eliminate these costs for various types of development.⁵

For those who want to preserve historic buildings in neighborhoods, compact single stair buildings also provide a less destructive way of incrementally adding housing to neighborhoods. When development on small lots is infeasible, it leads to the familiar phenomenon where nothing is built on vacant parcels until half a block is razed all at once — sometimes including several historical buildings in good condition — to make way for a large new apartment complex. Single stair buildings allow vacant lots and buildings that are truly tear-downs to be redeveloped into desperately needed housing, while leaving more of the neighborhood fabric intact.

We can see the benefits of single-staircase development in Seattle, which only requires a second staircase for buildings over six stories tall or with more than 4 units per story. The Jansen Court apartments below have 10 units, built on a small narrow lot (30 feet by 120 feet). The Aurora Avenue apartments are an affordable housing development, built on an even smaller lot (30 feet by 80 feet) — and thanks to Seattle’s single-staircase rules, it has 13 apartment units. Both buildings only have one staircase.

Credit: Mercatus Center 2024 report

By making more varieties of development feasible on the city’s small, narrow residential lots, single-staircase reform could make it meaningfully easier to add new housing throughout the city.

How Safe is Single Stair?

In recent years, multiple analyses have increased our confidence that single-staircase reform is safe and effective. We have learned from peer cities and states with a history of allowing taller single-stair buildings that show a strong safety record. More recently, additional cities have begun to pass laws allowing for more single-staircase apartments.

Pew’s single-stair report also provides a comprehensive overview on the safety of single-staircase buildings. One component of the report focuses on New York City, which has long allowed single-staircase buildings up to six stories. Examining data on hundreds of fire deaths in the city between 2012 and 2024, they found that occupants of New York’s 4-6 story single-staircase buildings had the same rate of fire deaths as other apartments in the city.

One reason single staircase buildings have similar safety records to double staircase buildings is that most fire deaths have little to do with the “means of egress” from a building. For the small number of fatal fires in New York’s single staircase buildings, Pew researchers found no evidence that these incidents were driven by the lack of a second staircase. The deaths occurred in the same apartment unit as where the fire started — in other words, having one versus two staircases was a secondary factor for most cases of fire danger in multifamily housing.

A similar pattern emerged in a recent legislatively-commissioned study in Minnesota performed by fire protection engineers and architecture consultants. The consultants found that since 2000, 75% of the state’s recorded fire deaths actually happened in the same part of the apartment as where the fire started — commonly the bedroom, common area, or kitchen. Zero fire deaths were caused by fires in hallways, stairwells, or ramps. This finding further suggests that the means of egress, including the number of staircases, is very rarely the key issue for fire safety.

In addition to studying prior fire safety outcomes, the Minnesota study also used fire safety models to estimate personal risk in different kinds of buildings. The study employed standard modelling techniques to estimate the probabilities of different fire safety failures in a building, and the resulting risk for the building’s residents based on the building’s fire mitigation technologies and exit routes.

First, the authors found that the presence of sprinklers was far more important to fire safety than the presence of a second staircase. Second, because single-staircase buildings tend to have much smaller footprints than buildings with two staircases, building residents still had relatively high abilities to evacuate smaller single-stair buildings.

When we evaluate the benefits to allowing single-staircase buildings, it’s also important to consider where people live under the status quo. In a separate research report, Pew found that multifamily apartment buildings built before 1999 have a fire safety risk about six times higher than newer apartment buildings. For a variety of construction and design-related reasons, new apartment buildings are far safer than older ones.

When evaluating reforms that make it easier to build new housing, such as single-staircase reform, we should also think counterfactually: building new housing creates new opportunities for people to move into newer, safer apartments. Alternatively, when we fail to build new housing, residents are forced to stay in older housing that is much less safe. The median home in Chicago was built in 1952.

In addition to New York City, many other places, both domestic and international, have safely allowed single-staircase buildings beyond Chicago’s current requirements. Dozens of countries — including Italy, Brazil, Denmark and China — allow buildings up to five, six, or far more stories to have only one single staircase. Yet most of these countries have far better fire safety records than the United States.

In recent years, other jurisdictions throughout the United States have taken note. Over a dozen states have passed bills initiating a study or rewriting of the local building code to allow taller single-staircase buildings. Reforms have also happened at the local level: Baltimore, Nashville, and Austin have all successfully passed single-stair legislation, contributing towards a growing reform movement.

The State of Single Stair Reform in Chicago

There are two ongoing legislative efforts that can bring single stair reform to Chicago, one at the municipal level and one at the state level.

Alderman Matt Martin (47th Ward) introduced a single stair ordinance in May of 2025 co-sponsored by Bennett R. Lawson (44th Ward), Anthony J. Quezada (35th Ward), and Ruth Cruz (30th Ward). It was referred to the Committee on Zoning, Landmarks, and Building Standards, where it has remained ever since.

Single stair reform is also a key component of Governor Pritzker’s Building Up Illinois Developments (BUILD) Plan. It is included in both the House and Senate versions of the legislation, which limit home rule powers and sets statewide standards for single stair buildings.

It is telling that champions for this reform emerged at both the state and local level over the past year. People who are serious about building more homes in Chicago and Illinois have recognized the new constraint on housing in the neighborhoods where people want to live, and they are working diligently to address it in good faith.

The Chicago Fire Department remains publicly opposed to any expansion of single stair, and the Department of Buildings has stayed silent on the issue. Encouragingly, the Mayor’s Office and Department of Buildings has recently rolled out other reforms to the building code, which would include ‘scissor stairs’ where two separate but interlocking staircases serve as an exit for buildings up to 15 stories. However, scissor stairs require prohibitively expensive concrete construction and have too large a footprint and to be practical for small lot apartment buildings, so single stair reform remains essential to enable new housing at this scale.

Conclusion

There is no ‘one weird trick’ to fix Chicago’s housing shortage, or transform underutilized lots into sorely needed housing. But single-stair is one of the most practical and effective steps we can take. If we follow the lead of peer cities, we can make it a lot easier to build the housing we need, in the places where it’s needed most.

1. There are certainly many parts of Chicago where development at any scale doesn't pencil under current conditions because land is too expensive or achievable rents are too low to justify a project. This is all the more reason to encourage compact neighborhood infill wherever the economics support it.

2. Illinois adopted the IBC as its statewide code standard in 2025 but exempted Chicago. States like Vermont and Georgia have adopted the NFPA code's egress standards, which allow 4 story single-stair buildings with up to 4 units per floor. NYC has allowed for single stair buildings up to 6 stories since 1938, and Seattle since 1977.

3. Keen observers walking in Chicago’s neighborhoods may have noticed mailboxes labeled with a number and letter, such as 1F or 2R. The number indicates the floor and the letter indicates the orientation, with F for front facing towards the street and R for rear facing towards the backyard and alley.

4. Some of these new rules were a reasonable response to reliability issues with external fire escapes and collapses of poorly built wooden porches. The issue is that modern effective fire safety devices like sprinklers and fire notification systems don't provide the same design relief in Chicago that fire escapes and porches once did.

5. While these kinds of cost savings won’t necessarily be directly passed down to tenants, they will still benefit affordability. Lowering construction costs will enable more housing to get built in Chicago, helping development that’s on the margin of financial viability. This will improve housing affordability through the more indirect, but equally important, channel of increasing supply in the city.