Single-Stair Reform: Eduardo Mendoza on Housing Affordability by Design Flexibility

Introduce yourself and explain for our readers how your leadership of the Livable Communities Initiative aligns with California’s push for single-stair reform and broader community housing development goals.

My name is Eduardo Mendoza. I am a trained planner, a former planner with the City of Los Angeles, and currently a Senior Research Associate with California YIMBY. I am also the Policy Director of the Livable Communities Initiative, which is now a 501(c)(3).

One of the main goals for the Livable Communities Initiative is to design what we think is true transit-oriented development and housing—development that can exist in a diverse urban context and offer alternatives in transportation, businesses, and residences. We see this as essential for the next stage of urbanism in the United States.

Housing advocates argue that double-stair mandates consume valuable living space and constrain design flexibility. Address how single-stair reform could advance housing affordability—not only in Los Angeles but statewide.

This reform does one thing very well: it allows individuals to build housing on smaller lots.

When I went to planning school, I was taught that to redevelop or build housing, you usually have to do land assembly—buying multiple adjacent lots, clearing them, and then building up. That model is tied to land-use density, design standards, and parking requirements, and has been the dominant paradigm in the U.S.

Other countries, and historically the U.S. before the mid-20th century, pursued lot-by-lot, incremental redevelopment. That’s what I call resilient redevelopment. For example, if someone owns a single-story barber shop and raises enough money, they could partner with a developer to add units above it. With this reform, that becomes much more feasible.

In terms of housing variety and affordability, several studies in the past four years have examined costs tied to stair and hallway requirements. Double-stair layouts add cost and reduce rentable square footage. They also push designs toward studios and one-bedrooms, because building code efficiency under current rules incentivizes them. Adding a single-stair option gives architects and developers more flexibility, enabling a greater variety of unit types and layouts. That’s why architects have strongly supported this reform.

Developers ultimately want to build on large or small parcels, rent out units, and generate long-term returns as neighborhoods appreciate. Given that single-stair reform could speed construction and increase supply, what mechanisms are being discussed alongside this reform to ensure it impacts affordability rather than just expanding development opportunities for developers?

That’s a really good question. You mentioned developers building to rent, but with single-stair buildings, the dynamic shifts. Developers, of course, want to maximize return—whether through larger assembled lots under current rules or smaller parcels under this reform. Their core goal is to build, rent, or sell units and generate long-term value as the surrounding area improves.

What’s important is that the unit layouts enabled by single-stair design often lend themselves to ownership models. These buildings make it easier to deliver two-bedroom, one-bath “starter home” units. If today in Los Angeles, a starter home costs $1.2 million and a townhouse is $1 million, units in these buildings could be priced lower—potentially around $700,000—because of economies of scale and unit value within total construction cost. That creates an entry point for new buyers who are currently priced out.

At the same time, it opens opportunities for the state to refine density bonus programs and inclusionary zoning laws, expanding them to cover homeownership as well as rental housing, or to adjust affordability covenants and financing structures. So, while this reform is not a silver bullet, it creates leverage points for aligning developer interests with policy goals on affordability.

In effect, you argue that new design opportunities based on this reform will support the construction of more affordable units?

Yes, and that ties directly to total land acquisition costs. In Los Angeles, there’s a 15–40% premium, and if developers can avoid paying that premium by building on smaller parcels, those savings could be passed on to tenants or buyers. The same applies to cost savings in actual construction.

Other jurisdictions (New York, Seattle, San Francisco, Denver, among others) are exploring or adopting single-stair reforms. Do you have any evidence that affordability has clearly improved due to this building type?

I haven’t seen a comprehensive study that looks only at single-stair buildings compared to other housing products. But even a simple Redfin or Zillow search shows differences in pricing between condos, townhomes, and single-family homes in those jurisdictions.

I also have an anecdote: a friend of mine bought a unit in a contemporary single-stair building in Williamsburg, New York, for under $800,000, which is a really hot market. He pays about $3,000 a month, while a similar-sized rental nearby would be much higher. That’s not scientific, but it illustrates the potential.

From the jurisdictions cited, are there examples that model the approach California is or should be taking regarding single-story buildings?

Yes and no. The mitigations associated with single-stair buildings are generally similar, but there are differences. In New York, you can only build them using Type I and II construction. In Seattle, you can use Type 5B, Type 5A, and Type III as well. California is moving in this direction now. Just last night, I attended a council meeting in Culver City, where they unanimously voted to adopt standards modeled on Seattle. Today, Los Angeles is holding a PLUM Committee hearing on the same issue.

It’s important to note that building-code updates differ from land-use debates. They are less political, more technical—tied to fire, life safety, and smoke-control studies. For example, Los Angeles has restricted single-stair buildings in high-fire severity zones, which is reasonable. New York’s sprinkler standards are less strict than Seattle’s. Seattle also permits wood construction, which California could allow, but only with higher safety standards to ensure equivalency with today’s protections.

A recent study found no difference in fire death rates between single-stair and multi-stair residential buildings in New York. But California has different building materials, sprinkler requirements, and fire risks. Fire-safety advocates remain skeptical, warning that loosening stair requirements could compromise emergency safety. What should California do to ensure both housing and safety goals are met?

A long question, but I will start by saying that I have the utmost respect for our fire service and for fire professionals. I know that in their job, their utmost priority is safety, and so in any discussion, they will always look at the worst-case scenario as the point where they defend. Which is, again, their job. Their job is not to be revolutionary or to push the boundary. Their job is to maintain safety.

Their positions and critiques against any reform are welcome. Whenever we advocate and push reform, we always look at these considerations very seriously. That being said, there are more reports than the Pew study. The Pew study has gotten a lot of attention, but other technical reports analyze smoke spread, fire spread, egress, and fire loss—reports that go much more into detail on the efficacy of these mitigations and layouts within single-stair buildings.

Through these reports and science—purely technical, scientific reports—I’ve arrived at my conclusion that certain mitigation strategies are effective. Nothing will ever be 100% safe. If we looked at the world like that, we wouldn’t be driving cars or even walking outside….but if we feel comfortable that a certain amount of safety is adopted through these measures, and the outcomes are verifiable through empirics, research, and study, then we are okay with moving forward.

I have a lot of reasons I could share after this conversation as well, but that being said, whenever we adopt these standards in California, I am always adamant in saying we should always offer the safest outcome possible that still leads to the construction of these buildings.

You’ve helped elevate this issue through advocacy, including the Single-Stair Design Competition. Briefly talk about launching this competition, and if any, what design innovations have surfaced.

One of the main concerns—outside of fire safety—came from planning departments. They told me, “Ed, this is great, but U.S. lots are too deep and too narrow. It works in New York and Seattle, but conditions are different here. The standard 45 by 135 lot just doesn’t cut it.” I challenged that. I respected their opinion, but I wanted to test it. 

I posed the challenge to architects: design these buildings using Seattle-based mitigations. Show us what they could look like on a standard lot. On a typical North American commercial lot, on very small townhouse lots, like in San Francisco, Baltimore, or D.C.

Since launching the competition, the entries I’ve received have been phenomenal. The creativity is there. Reviewing some of them, I could easily imagine myself or friends living comfortably in those layouts.  Right now we’re in the judging phase, and once winners are determined, I look forward to releasing all the building plans to the public.

Looking at the design constraints and goals of the Single-Stair Design Competition, it's notable that setbacks, open space, and FAR requirements were eliminated. Why?

In North American planning, a lot of “truths” about how buildings are supposed to look are actually driven by building code standards. I’ve studied this in detail. Many U.S. buildings don’t face the street or a rear courtyard—they face the side yard. That pattern is based on code: if you have an internal corridor, all units must face a side. Developers then maximize that by aligning units along the long side of the building.

Single-stair design breaks that dogma. If jurisdictions adopt single-stair reform, planning and design standards could change drastically. Buildings could incorporate more open courtyards, greener spaces, and layouts closer to what you see in Barcelona or Bordeaux—but in a North American context. Lot sizes in New York are definitely smaller. In California, there’s a greater variety, and many lots are larger.

Related to the design differences of lots based on size, depth, etc., is that connected to the decision to eliminate setbacks, open space, and FAR requirements?

Absolutely connected, because our lots tend to be deeper and narrower, planning departments—working from the existing code—design standards around side-yard setbacks. They’ll say: “If the only light we get is through a side-yard setback, then maximize that.”

This typology says: you don’t need a side-yard setback. You have a whole courtyard in the middle of your building, and that provides more natural light than any side-yard setback ever could.

Lastly, as a former planner, you’ve been trained to go beyond the building envelope, while traditionally, planning long has encompassed siting, managing growth, and creating more holistic neighborhoods. How does your work with single-stair reform advance that broader goal of building livable places?

Fantastic question, and I always appreciate putting my planning hat back on. In short, we are challenging cities to be more proactive…and this actually gives planners more work to do.

It used to be that a planner could say: “On this third-of-an-acre site, you must provide certain conditions, certain open space, certain public amenities.” But if someone is building on a 25-by-100-foot lot, you can’t be as onerous. The only thing that can fit on their site is a building and maybe a courtyard. So this reform poses a challenge—and I think it’s a good challenge. The challenges of single-stair reform force planners to ask more holistic questions about those traditional aims of planning you mentioned. 

With this reform, they should now be asking: How do we design communities around these single-stair buildings and take advantage of this potential? It supports slower, more incremental, more resilient infill growth.