This Parisian Apartment Building Could Only Work With Single Stairs

In much of the world, small apartment buildings have single exit stairs. Architect Michael Eliason has explained how this makes it possible to build better housing on smaller sites, but the idea is controversial in North America. When we recently featured a 5-story mass timber building in Australia with a single stair, comments ranged from "DEATH TRAP!" to "Made out of wood???? Sounds like a double fire hazard with no other stair exit." One even noted, "Single stairs means trample deaths and smoke inhalation. There's a reason the U.S. began requiring more than one set of stairs per building."

But this little apartment building in Paris demonstrates how the ability to build with a single stair makes it possible to utilize smaller sites. And if people thought the Australian building was a double hazard, they may find this one truly shocking: Wood construction! Single stair! It's a winder! And there's no elevator!

Designed by Mobile Architectural Office (MAO), the building is on a very small corner site in a smart central part of Paris. According to the firm: "Access to the flats is via a bright, walk-through hall overlooking Rue du Terrage. On the upper floors, all the dwellings are double or triple-oriented and have large windows offering a maximum of light to the inhabitants."

This is a point Eliason has made about single-stair buildings: It is much easier to have multiple orientations and cross-ventilation.

Construction is much faster when you build out of prefabricated mass timber. MAO noted: "The building develops a structural principle based on prefabricated wood, with solid facades and floors (from the Basque Country). This principle has allowed the development of a very low carbon site and the assembly of the structure on five levels in 10 days. Cross-laminated timber panels placed on the facades and partitions support cross-laminated timber panel floors."

The building is seriously low-carbon, with the mass timber structure from Egoin, STEICOflex wood fiber insulation, and larch cladding in the little courtyard. Even the flooring is made of vegetal fibers, what we call linoleum. Only the ground floor is made of concrete to facilitate long spans in the commercial area.

A lot of wood is left exposed within the apartments themselves. The top three floors are like two townhouses, three levels high with a roof deck on top. This is likely how they managed to build it without an elevator; many building codes don't require them if the top entry level is not too far from the grade. There is definitely room for debate about whether this is a good idea—we usually promote universal access. However, it is a very tight site.

Lots of wood, and lots of windows and doors opening onto balconies. This is a critical part of the safety plan in single-stair buildings; you do have a second way out of the apartment—on to the balcony, which is close enough to grade that you can get rescued by the fire department.

All of the mechanical equipment for ventilation and the boiler serving the hot water radiators is in each unit. Not much heat is needed because of the "very high thermal resistance" of the walls, which appear to be about six inches of wood fiber insulation.

Detailing in mass timber is so straightforward and elegant. You have a floor panel clipped to a wall panel; put your steel siding on the outside and your insulation on the inside. No wonder it all goes up in a couple of days.

So for all the single-stair skeptics, remember that it is only six residential units in total. Most North American buildings with corridors and two stairs have dozens of units and get big and long to justify the costs. Paris and Vienna look the way they do because you can build this way.

As Eliason noted, "[These buildings] are the smaller, fine-grained urbanisms that make for great cities we talk about so often. They can be family-friendly, with a diversity of unit types, and are both space and energy-efficient. They are also accessible, as buildings on both continents require elevators on projects like this and many in Germany are barrier-free or adaptable. Most importantly, they are legal. Maybe we should follow suit."

North American cities could have more quality housing on more beautiful streets if we could build little buildings like this too. Fortunately, there is a lot of action happening on this front; architects like Eliason and Conrad Speckert are hard at work at this. Check out Speckert's website and, in particular, his Manual of Illegal Floor Plans, showing dozens of wonderful projects all over the world that cannot be built in most of North America. And dream of Paris.