It would not be much of an exaggeration to say that, for more than a century, American urban planning has been devoted to layering on ways to all but ban apartment buildings. And so, as the US now tries to shift out of the anti-density gear that’s driving our housing affordability crisis, policymakers are finding that there are obstacles hiding in a lot of places. Like, a lot.

States and cities are already working, little by little, to roll back the foundational problem often blamed for the current housing shortage: our rigid system of zoning, which dictates what kinds of buildings can be built where. Exclusionary zoning is the reason that it is illegal to build anything other than a detached single-family home on most residential land in the US, making homes scarce, spread out, and unaffordable.

Less appreciated but perhaps just as culpable are the labyrinthine rules governing how new homes must be built — the materials, safety features, and other requirements that make up the entrails of American buildings.

Increasingly, housing abundance advocates, home builders, and policymakers are discovering that fixing zoning is merely the entry point into a gauntlet of other constraints. Especially in the quest to build more “missing middle” housing — duplexes, triplexes, and small and mid-size apartment buildings. “Simply allowing a fourplex on paper does not guarantee that one will be built,” John Zeanah, the chief of development and infrastructure for Memphis, wrote in a recent report on non-zoning barriers to housing for the Center for Building in North America, a nonprofit that advocates for reforming US and Canadian building codes to align them with other affluent countries.

Why? Even as cities re-legalize the traditional housing forms that once supported economic mobility and urban vitality in America, extremely strict, sometimes ill-considered building codes and other requirements can quickly make them financially infeasible to build.

Many of our building codes are rooted in important safety needs — they’re the reason why residential fire deaths have been greatly diminished and why we can enjoy convenient electricity without getting shocked all the time.

But in the US, a morass of construction codes, fire safety requirements, utility rules, and even tax policies, treat even small multifamily buildings fundamentally differently from the way they treat single-family homes. Anything larger than a duplex is regulated under building codes as a commercial building rather than a residential one, even though apartments are, obviously, residences. That saddles multifamily homes with costly construction requirements that housing advocates argue are not evidence-based and can balloon the cost of building to crippling levels.

As a result, it costs significantly more per square foot to build multifamily homes in the US (and in Canada, which has similar codes) compared to single-family homes, a report from the Pew Charitable Trusts and the Center for Building in North America found last year. This is not the case in peer countries, because of the economies of scale that often otherwise come with building multifamilies.

If the words “building codes” make you want to crawl into bed and take a nap — I get it. But consider that all of this converges on a more profound point about American culture. At seemingly every level of policy, we penalize and stigmatize apartments as though they’re a second-class form of housing. The last century-plus of urban planning has shaped the deeply rooted American reverence for single-family home ownership, adding up over time to thousands of little rules that stack the deck against denser, more affordable homes.

Building codes are “supposed to be this technocratic process focused on safety, when in reality there are all sorts of values and biases embedded within them,” Jesse Zwick, a Santa Monica city council member and author of a recent report on American building codes, said on the UCLA Housing Voice podcast last year.

Here are just a handful of ways that seemingly obscure rules can thwart building missing middle housing in America.

1. The cost cliff for small multi-family buildings, explained by… sprinklers

Building codes revolve, to a great extent, around fire safety — quite understandably and importantly, given our country’s traumatic history with deadly fires. But the process by which the codes are written in the US, and their appropriateness for small- and medium-scale multifamily homes, is under growing scrutiny.

In the US, building codes are drawn from models developed by a private organization, the International Code Council (despite the name, though, its codes are primarily just used in the US). They’re then adopted as law at the state and local levels. Single-family homes, townhomes, and duplexes fall under the ICC’s residential code, while anything with three or more housing units — triplexes and up — are regulated under a code “designed for everything from apartments and offices to airports and stadiums,” the Center for Building report notes.

That code, known as the International Building Code, is not one-size-fits-all — it does have different rules for different kinds of buildings. Still, it is often “over-scaled” for small multi-family homes, Zeanah writes. “The leap in complexity from duplex to triplex is dramatic” in terms of requirements. Most new multifamily buildings must have extensive sprinkler systems, along with other commercial-grade fire safety equipment.

Who, you might be asking, could be against sprinklers? They’re very effective at putting out fires, and in many contexts, they may make perfect sense, like in apartment buildings with dozens or hundreds of units.

But everything comes at a cost — and the problem is that sprinklers cost so much to install and create such high ongoing maintenance expenses that they “can be a make-or-break factor” for small multifamily home construction, Zeanah writes.

Since small apartment buildings aren’t radically different in scale from single-family homes and duplexes — triplexes can have the same square footage as a large single-family home — Zeanah’s report argues that cities and states should consider amending their codes to allow flexibility in that requirement that would permit developers to take advantage of other fire safety options.

Fireproofing as a pretext for banning apartments

A bit of historical context can help shed light on the predicament we now find ourselves in. Over a century ago, the Progressive-era reformer Lawrence Veiller, who helped shape the foundation of America’s exclusionary zoning laws, essentially called for using fire codes to regulate multifamily housing out of existence by making it too expensive to build.

“The easiest and quickest way to penalize the apartment house is not through requiring larger open spaces, because I think that would be unconstitutional, but through the fireproofing requirements,” he said. “In our laws let most of our fire provisions relate solely to multiple dwellings, and allow our private houses and two-family houses to be built with almost no fire protection whatever.”

To be fair to Veiller, he was writing during a time of horrific tenement fires, and he probably couldn’t have imagined a future like ours, where apartments are even safer than single-family homes.

Zeanah recounts an example of a small developer in Memphis, Andre Jones, who struggled to build fourplexes because sprinkler systems would have been financially unworkable. So Jones and Zeanah worked together to find a solution, which eventually helped lead to a Tennessee law allowing many small buildings up to four units to forgo sprinklers if they have two-hour fire-resistant separation between walls, floors, and ceilings.

There’s precedent for such exceptions. The code that governs single-family homes and duplexes has required sprinklers in new builds since 2009, but nearly every US state has passed a law exempting single-family houses from that rule.

The residential code itself, Zeanah told me in an interview, was created as an exception from the International Code Council’s default building code, and it’s not clear why the council chose to carve out just one- and two-family structures rather than make the cutoff at triplexes, fourplexes, or elsewhere.

Meanwhile, modern buildings are already much safer than old ones, and codes that are designed for safety but end up making new homes so expensive to build that people remain in old ones may have net negative effects on safety. Many critics of US building codes have pointed out that the ICC creates these rules without meaningful cost-benefit analysis to determine whether a requirement is worth its costs to housing supply, affordability, and safety.

Gabe Maser, senior vice president for innovation and growth for ICC, told me in an interview that there’s little evidence that home construction costs significantly contribute to housing prices. “No peer-reviewed study has found that building codes have any appreciable implications for housing affordability,” he said. And there is, to be sure, a great deal of uncertainty and complexity here — more research is needed on the subject. Some research suggests that building costs don’t have much to do with home prices, especially in the most expensive cities, where prices are bid up more by sheer scarcity than by the direct cost of building. But that evidence comes largely from single-family homes.

Evidence for apartments, which have different underlying economics than single-family homes and are regulated by stricter building codes, has found that construction costs do drive housing prices. A recent working paper by Michael Eriksen, a Purdue University economist, and co-authors Deniz Besiktepe and Claudio Martani modeled how recent building code changes impact the rents that landlords need to charge to break even, finding an increase of about $169 to $279 in monthly rent on a theoretical two-bedroom apartment in a new-construction three-story building.

Many small-scale homebuilders also say that code requirements make missing middle projects infeasible. “When a project is no longer financially viable, it simply doesn’t get built, which means its impact won’t show up in observed [housing] price data,” Eriksen told me in an email.

2. Stair regulations make our buildings more expensive and less liveable

Almost every new apartment building more than three stories tall in the US is required to have at least two staircases, to provide a second fire escape route (and sometimes even smaller buildings have to have two as well). That adds hundreds of thousands of dollars to the cost of construction and cuts down liveable square footage.

To accommodate two staircases, architects typically design buildings with a long hallway running down the center, called a “double-loaded corridor,” with apartments on either side. This tends to also push toward bigger buildings. Single-staircase buildings, on the other hand, can arrange apartments with a smaller number of units opening onto a single central staircase, opening up more space for larger apartments, including more units that can stretch across multiple sides of a building for more natural light, without it needing to be bisected by a central corridor. They can also have more flexible layouts that are more amenable to family-sized apartments with three or more bedrooms.

The Pew Charitable Trusts

Countries in Europe and elsewhere in the world, plus Seattle and New York City, already safely build single-stair structures, and research has found that they do not have a worse safety record. Modern US multifamily homes are already significantly safer than single-family homes, likely thanks to all of their other fire safety features, according to research from Pew.

But I won’t dwell more on this debate here, because Vox’s Rachel Cohen Booth already covered it in a fantastic story last year.

**3. When a triplex suddenly needs its own architect **

Homes that fall under the residential code can be built according to a pre-prescribed recipe book that ensures the safety of various structural elements, like their ability to withstand wind. But want to build a residential building with more than two homes in it? In many places, that means you’ll need to hire a dedicated architect or engineer to draw up and sign off on custom plans, Zeanah writes in the Center for Building report.

This might be perfectly reasonable for a 100-unit building. But it means that small developers looking to build a triplex or fourplex, for example, face higher upfront costs before they’re approved to build what is ultimately similar in scale to a single-family home, Zeanah points out. He recommends that governments consider allowing modest multifamily buildings to use pre-designed standards that are already allowed for single-families and duplexes.

4. The US seems unusually bad at building elevators

Elevators are a marvel of modern life, making apartment living far more viable and accessible to people with a range of physical abilities. But “the United States and Canada have the most expensive elevators in the world,” sometimes costing upward of three times what European elevators do, Stephen Smith, executive director of the Center for Building, writes in a comprehensive report on elevator policy.

Regulatory factors explain most of that gap. Newly installed American elevators must typically be twice as big as their European counterparts, big enough to fit a seven-foot stretcher lying flat and a wheelchair’s turning radius. In Europe, whose elevators are essentially the global standard, typical elevators are big enough to accommodate a wheelchair and a person standing behind it, but not a wheelchair radius; the buttons in European elevators are placed on the side, so that wheelchair users can access them regardless of whether they’re facing forward or backward.

The stretcher size requirement, meanwhile, appears to provide particularly clear evidence of a lack of rigor in US building codes: It was increased to seven feet about 20 years ago with perfunctory research, and the cost impact was stated as “none,” Smith’s report found. Prior to that, the requirement had been for elevators to fit a stretcher up to 6 feet 4 inches long. US paramedics are already trained to navigate smaller spaces by, for example, tilting stretchers.

Today, the International Code Council requires proponents of new rules to add more documentation to justify cost impact claims, and Maser told me these claims are closely scrutinized when deciding whether to adopt a rule.

Besides code requirements, US labor union rules effectively bar some of the most productive methods for building elevators, like factory preassembly, Smith writes. And the US, along with Canada, uses technical standards for elevator construction that are incompatible with the rest of the world, effectively “walling us off from the global market” for elevator parts. If you’ve ever had to live with a broken elevator that took ages to repair, that might be why!

Rather than making American homes safer and more accessible, these policies more likely mean, as Smith suggests, that fewer elevators are built, fewer apartment buildings are built, and more of our housing stock is comprised of low-density, inaccessible homes.

The bigger picture

The lesson of our housing crisis is straight out of Econ 101: If you perpetually raise the cost of building something, it will not be built at all. The barriers go beyond building codes, too, to things like property taxes: Tennessee, for example, treats apartment buildings as commercial property and taxes them at a higher rate than single-family homes — a prime example of how we subsidize homeownership at renters’ expense.

When you don’t build something, there will be little constituency to advocate for it — and in this case, for right-sizing codes to accommodate it. For all the energy spent on the housing debate, the costs of mandating perfect construction have escaped meaningful public deliberation.

That brings us to the deeper lesson about building codes. Zoning, right now, is a problem of too many state-prescribed rules. But with building codes, the problem could be interpreted as the opposite — a lack of government capacity. The US has effectively handed off building code rulemaking to a private nonprofit that is enmeshed with private interests, including homebuilders and materials manufacturers. “I think we’ve really outsourced this decision to, honestly, a group of lobbyists, building manufacturers, labor unions,” Eriksen, the economist, said.

While only people in government roles have a final vote on changes to the ICC’s codes, critics have argued that the organization’s processes are not well set up for these public servants to make well-informed decisions. They vote on a huge volume of changes that they aren’t always equipped to understand, and the ICC’s committees, comprised of industry and nonprofit employees as well as public servants, are very influential in whether a proposed change succeeds.

Maser, of the ICC, though, stressed that proposed code changes are evaluated with a “high level of scrutiny.” They’re “thoroughly reviewed by a wide swath of experts,” he said, and “housing affordability is thoroughly vetted through the process.” Any member of the public can submit a proposed change if they’re unhappy with the current code, and code updates happen frequently enough (every three years) that a good idea can be implemented relatively quickly. Right now, a proposal to allow more single-stair buildings is working its way through the code change process.

In the near term, housing advocates are organizing to modify building codes state-by-state, such as legalizing more single-stair buildings and allowing greater flexibility for meeting fire safety standards in small multifamily buildings.

That approach is making real progress, though its piecemeal nature makes it inherently slow. In an ideal world, some advocates hope that the federal government can create a new, more transparent, and publicly accountable system for regulating the buildings in which we spend so much of our lives. Many European systems, for example, emphasize “performance-based” standards that mandate certain safety outcomes, rather than strictly dictating the tools (like sprinklers) that must be used to get there.

That may be a vision worth aspiring to, as we slowly feel our way out of the decades-old planning mistakes that have turned as basic a human need as housing into a luxury good.