Last night I asked the American building reform advocates on Bluesky about different layouts and why developers don’t build them. I got different answers from different advocates about why the layout I’d just mocked of family-size apartments with two staircases isn’t being built in the US, some about regulations, but Mike Eliason said what I was most afraid of hearing: it’s doable but it’s more profitable to build small apartments. My conclusion from this is that while American and Canadian building regulations remain a problem and need to be realigned with European and Asian norms, they are a secondary issue, the primary one remaining how much housing is permitted to be built in the first place. Developers will keep building the most profitable apartment forms until they run out of the most profitable tenants.

The mockup

The following mockup has a scale of 1 meter = 20 pixels, so the building is overall 18 meters by 30. This is a point access block rather than a double-loaded corridor (see definitions here), but it also has two staircases, emanating from the central access block. Each floor has four apartments, each with three bedrooms and two bathrooms, the ellipses in the image denoting bathtubs. The windows are top and bottom, but not left and right; these are single-aspect apartments, not corner apartments.

On Bluesky, I said the floorplate efficiency is 94%; this comes from assuming the step width and landing length are 1.1 meters each, a metrization of the International Building Code’s 44″, but to get to 94% assumes the staircase walls are included in the 1.1 meter width, so either it’s actually 90 cm width or, counting wall thickness, the efficiency is only 92.5%. The IBC allows 90 cm steps in buildings with an occupancy limit of up to 50, which this building would satisfy in practice at six stories (a three-bedroom apartment marketed to a middle-class clientele averages closer to two than four occupants due to empty nests, divorces, guest rooms, and home offices) but not as a legal limit. Regardless, 92.5% is average by the standards of European point access blocks, whose efficiency is reduced because the apartments are smaller, and very good by those of American double-loaded corridors.

Now, to be clear, this is still illegal in many American jurisdictions, as Alfred Twu pointed out in @-replies. The building mockup above has two means of egress, but the typical American code also requires minimum separation between the two staircases’ access points. This is an entirely useless addition – the main fire safety benefits of two staircases are that a single fire can’t interpose between residents and the stairs if the two staircases are at opposite ends of the building, but that’s not legally required (quarter-point staircases are routine), and that the fire department can vent smoke through one staircase while keeping the other safe, which does not require separation. Nonetheless, this is not the primary reason this isn’t getting built even where it is legal, for example in jurisdictions that permit scissor stairs or have a smaller minimum distance between the two staircases, like Canada.

I was hoping the answer I’d get would be about elevator costs. The elevator in the mockup is European, 1.6*1.75 meters in exterior dimensions; American codes require bigger elevators, which is by itself a second-order issue, but then installation costs rise to the point that developers prefer long buildings on corridors for the lower ratio of elevators to apartments. But nobody mentioned that as a reason.

The rent issue

Mike Eliason responded to my question about why buildings like the above mockup aren’t being built by talking about market conditions. The above building, with 540 m^2 of built-up area per floor, can host four three-bedroom apartments, each around 127 m^2, or it can host 16 studios, each around 29 m^2. In Seattle, the studio can rent for $1,500/month; the three-bedroom will struggle to earn the proportionate $6,000/month.

It’s worth unpacking what causes these market conditions. The three-bedroom is marketed to a family with children. The children do not earn money, and, until they reach kindergarten age, cost thousands of dollars a month each in daycare fees; if they don’t go to daycare then it means the family only has one income, which means it definitely can’t afford to compete for building space with four singles who’d take four studios, or it has parents in the immediate vicinity, which is rare in a large, internally mobile country. The family has options to outbid the four singles, but they’re limited and require the family to be rather wealthy – two incomes are obligatory, at high enough levels to be able to take the hit from taxes and daycare; the family would also need to be wedded to living in the city, since the suburbs’ housing is designed entirely for families, whereas the singles take a serious hit to living standards from suburbanizing (they’d have to get housemates). In effect, the broad middle and lower middle classes could afford the studios as singles, but only the uppermost reaches of the middle class can pay $6,000/month for the three-bedroom.

In economic statistics, imputation of living standards for different household sizes takes this degressivity of income – $6,000/month for a family of four is a struggle, $1,500/month for a single is affordable on the average US wage – and uses a hedonic adjustment for household sizes. example by taking the square root of household size as the number of true consumption units. To INSEE, a family of four has 2.1 equivalent consumption units; elsewhere, it’s a square root, so it has 2 consumption units. A rental system that maintains a 4:1 ratio has no way for the family to compete.

The upshot is that the developers need to run out of the tenants who can most easily afford rent before they build for the rest. Normally it’s treated as a matter of distribution of units among different social classes, but here it’s a matter of the physical size of the unit. This is why YIMBY first is so important: eventually developers will run out of singles and then have to build for families.

The biggest housing activism push in North America right now has moved on from YIMBYism to housing reforms to allow single-stair mid-rise buildings, called point access blocks. My off-hand reference to this last post ended up being the main issue debated in comments; this compounds a post by Matt Yglesias from November that I’ve been meaning to respond to, since he starts working off of some examples of double-stair buildings on corridors in an even older post of mine about the Kowloon Walled City in My Backward (KWCIMBY) meme. I strongly respect the main point access block activists pushing the issue, like Stephen Smith, so I’d like to revisit the KWCIMBY post and explain what I’m doing there, while also pushing back against some of the more iffy claims portraying point access blocks as not just more efficient but also inherently better for families. In short, both forms of housing are generally easier to build in a more affluent society with higher expectations, and some of the comparisons come from that.

What are the point access block and double-loaded corridor?

An apartment building can arrange its apartments on each floor in one of these ways. The KWCIMBY post assumes double-loaded corridors, as in the diagram below:

In each of these buildings, there are two staircases, as required by American and Canadian law; the first building has scissor stairs, forbidden in most of the US but allowed in New York, whereas the second separates the two staircases into opposite sides of the corridor. Apartments are on both sides of the corridor, with one aspect of windows except the corner units, hence the term double-loaded.

This building form is practically unheard of in European apartment buildings. Only one staircase is required per building, so architects instead slice the buildings into thinner pieces, with one staircase and an elevator and apartments radiating from the common area, called a point access block:

Each of the four access points has an elevator and a staircase; the first example has four apartments per floor, with one aspect per unit, whereas the second has two, with two aspects, both north and south. The result is more elevators and staircases per net floor area, but less corridor area; the floorplate efficiency is notably higher, 92.5% in the first case and 94% in the second case, compared with 89.5% in the first case of the double-loaded corridor and 86.67% in the second. This is one of the reasons Stephen is so focused on elevator costs.

All four buildings are 20 meters by 80, except the last, which is 14 by 80. 20 meter wide residential buildings are more or less unheard of in Central Europe – I see a few that are 18, in what look like higher-income neighborhoods to me. In contrast, 14 is standard in Central Europe, with some buildings looking like the above diagram, and others, almost always older ones, having wings that are still around 14 meters wide but end up with an area-to-external-width ratio of 8-9 meters, rather like a 16-18 meter wide building without wings. In practice, on a 100*100 block, we’d never have two buildings looking like an equal sign but rather an enclosed rectangle, with or without wings.

What about the single-loaded corridor?

A third housing typology puts all apartments on a corridor, but only in one direction. The corridor is then in the open air, and apartments have windows on both sides, to the corridor and in the opposite direction. I lived in such a place for a year in Berlin. This is not unheard of, but still rare. The width of such buildings is limited by the need for apartments to stretch all the way, limiting them to at most 14 meters and usually less.

The resulting floorplate efficiency is low, which turns this into a question of how much cheaper it is to build an external corridor than an internal one. When I asked on Bluesky, I was given ranges for the answer, from an external corridor being 25-50% cheaper to its being if anything more expensive. Temporary worker housing tends to use this form because it is built to lower standards, in which the external corridor is just some barred steel without protection from the elements above, which should reduce the cost of the corridor. This form still exists in permanent housing, with concrete corridors that offer protection from rain, but it’s less common than the other two.

Point access blocks and families

The biggest selling points of the point access block are that it has better floor plate efficiency and that it permits units with multiple aspects to allow for cross-ventilation and for strategic placement of rooms (living room facing the street, bedrooms facing the quieter internal courtyard of the euroblock). This is bundled with other issues, at the same time:

• In Europe, buildings are almost never built out of wood, and if they are, it’s usually mass timber. This means that the cost of construction is proportional to floor area, largely linear in the number of floors for a given footprint. North American construction uses light wood on a concrete podium, sharply limiting height to six to seven stories, hence the preference for thicker buildings to increase floor area. In turn, light wood is less safe in fires – but those codes don’t exempt concrete buildings from the two staircase requirement.
• The double-loaded corridor has units so deep that bedrooms come with their own bathrooms and walk-in closets. Absent these, the maximum usable depth of a bedroom is about 6 meters. Bathrooms cost more to build per square meter than bedrooms and living rooms, which drives up construction costs.
• The double-loaded corridor makes it easier to build units with fewer bedrooms – it’s just a matter of how much corridor width the apartment takes, so costs are linear in the floor area of units. The point access block instead prefers larger units, in square meters, since larger apartments have higher floorplate efficiency, and it’s routine to build a cheaper three-bedroom, one-bathroom unit.

The last two points have been used by some urbanists, especially more conservative ones, to argue that the point access block is inherently family-friendlier. The argument made by Mike Eliason (who’s not at all conservative) is that Seattle, where he’s based, builds multifamily housing rapidly but all of it is studios and one- and two-bedroom units, on the expectation that families with children should eventually move to the suburbs.

More conservative people even relate that with low urban American birthrates, which always comes off as strange to me given how low European birthrates are. The one developed country with above-replacement birthrates, Israel, doesn’t use any of these forms, but instead has independent buildings, some mid-rise and some tall – and there’s consensus among European and American urbanists that tall buildings are bad for families. At any rate, the Israeli sociologists I read on the subject, like Sergio Della Pergola, attribute Israeli birthrate exceptionalism to other issues than built form, just as Singapore’s Paulin Tay Straughan attributes the very low birthrates in rich Asia to other issues.

The difficulty of relating the issue of housing forms with that of apartment sizes is that housing a family requires a lot of apartment space to go to people who are not working, because they are children. If housing is expensive due to high construction costs, restrictions on building, or both, then housing will be built for the rich, which means not just high-income earners, but also households with a high income per person, which are almost always ones without children. A developer building a double-loaded corridor making a choice between a one-bedroom, say 6*9 meters, and a three-bedroom, say 12*9 meters, will choose the former if two independent households can outbid a family. This is getting to the point that in urban America, it’s normal for unmarried adults to live with housemates, because there are a lot more three- than one-bedroom apartments in cities that don’t build much housing, like New York or Boston.

The family could outbid the single person, but not in all circumstances. A two-income family can do well, and the working adults are likely to be older than the single person and thus higher earners. A landlord of a fixed apartment choosing who to rent to would also prefer the family to the group of three to four housemates – the family is more stable, divorce being far less common than housemates leaving with little prior notice. But not all families have two earners (and the social conservatives who are most anxious about family housing tend toward one income, not two), or two middle-class earners, and so far American developers haven’t yet run out of demand for single people and childless couples to build for.

Point access blocks and wealth

In a way, the point access block has benefits that aren’t yet unlocked in Europe. Higher wealth is spent on, among other things, bigger dwellings. The double-loaded corridor in a way bakes in assumptions of private bathrooms, essentially spending income on higher-cost elements. But it’s possible to do the same with a point access block. The point access block ends up more efficient when apartments are bigger, because it’s limited by number of units per floor, and the bigger the units, the smaller the proportion of the unrentable common areas.

Speaking of common areas, higher wealth doesn’t necessarily demand of them. If the expectation is that people should have a washing machine and a drier at home rather than in a common area, then the demand for such an area shrinks. Trash rooms take up more space, but then higher wealth, as opposed to higher inequality, means not just that the demand for trash rooms is higher but also that the supply of workers to staff them is scarcer, and at the end of the day people can just haul trash bags to a collection point in the courtyard or a side room on the ground floor. Trash chutes are an innovation that doesn’t take up common space (for one, they can be installed in-unit, especially if there are only two units per floor anyway). High-end condo amenities like private gyms are usually provided at the scale of an entire building rather than a floor, and a complex of interconnected buildings is likely to have just one either way.

In the examples I posted above, in a way I baked in a wealth assumption, in that the option with two units per access point assumes those units average 132 m^2, which is very high for Europe; the norm for high-end buildings here is three units, with slightly lower combined floor area than 264 m^2, and the same or a hair higher circulation area to allow for a third door, with the smaller apartment usually only having one aspect of exposure. A 132 m^2 unit, in effect 10*14 with slight recessing at one end, would generously have four bedrooms, likely configured as three actual bedrooms and a private office or guest room. The intended users would be families of means, but then again new housing tends to be built for this class, and over time, growth and abundance make the standards that today mark middle-class wealth more widespread across classes. The working class once didn’t have indoor plumbing.