Rightly or not, prefabricated buildings have a reputation for being boxy, boring and repetitive. None of those words describe Porto’s Hoso tower, a 13-storey student residence immediately distinguished by its articulated concrete exoskeleton and oval form. Designed by local practice OODA, the project leveraged prefabricated components to facilitate an accelerated construction timeline — and create a strikingly individual building.

For the architects, the process was guided by the qualities of the circular form. Yet, while the simplicity circular geometry allows for spatial efficiency, it tends to complicate construction. During an on-site concrete pour, for example, curved walls typically entail a slower process, and invite a greater potential for error, compared to the straight lines and right angles of rectilinear forms. With a prefabricated structure — which was also designed for easy, stackable transport — the on-site complexity is significantly reduced, facilitating a relatively quick construction schedule of just 14 months while maintaining high build quality. According to the designers, the process “reduced construction costs and the timeline by 30 per cent.”

Facilitating a rounded form without incurring the added costs and logistical complexities that would typically result during construction, the use of prefabricated concrete panels allowed the designers to leverage the circular shape to create streamlined interior circulation. Inside, the 9,350-square-metre building is organized around a central core of stairs and elevators, with each residential floor framed by a simple circular hallway connecting to individual student suites.

By maintaining a compact core and minimal wasted space, each of the residences enjoys a more generous interior. In a typical suite, a small kitchenette and bathroom meet the entrance, with the bed and living space positioned by the window, where the wedge-shaped room widens. Outside, a balcony extends the space, and the building’s extruded concrete structure works to mitigate both solar heat gain as well as noise from a nearby highway, all while fostering a sense of privacy seldom found in student housing. (On the top floor, meanwhile, a communal garden offers an attractive hangout space, complementing shared ground floor amenities.)

The thoughtfully resolved layouts and circulation are also the product of a deft egress strategy. At the heart of the Hoso tower, the two stairs are organized as a “scissor stair,” which combines dual sets of steps within a single enclosure. This allows taller buildings to meet code requirements for two points of egress while maintaining a spatially efficient envelope — and avoiding the double-loaded corridors typically imposed by two discrete stair volumes.

A typical floor, showing the spatially efficient circulation at the heart of the building, facilitated by a scissor stair and compact elevators.

Yet, while the prefabricated panelized construction offers an international case study to replicate, much of the building’s success hinges on liberal European regulations. As Canadian building code specialist Conrad Speckert explains, a scissor stair is relatively common across many jurisdictions, although “the model code for the United States… does not permit scissor stairs to count as two separate exits.”

The staircase isn’t the only element of the Hoso tower that wouldn’t be possible under North American building codes: The building’s relatively small elevators are a case in point. Writing in the New York Times, Stephen Smith argues that “The United States and Canada have also marooned themselves on a regulatory island for elevator parts and designs,” mandating exceptionally large minimum sizes compared to Europe and the rest of the world. (Where European accessibility codes require lifts to accomodate a wheelchair, North American size minimums mandate room for both a stretcher and support personnel, inadvertently making them harder and more expensive to build — and resulting in substantially fewer elevators per capita).

Indeed, while North American architects can take inspiration from elements of the design, the striking Hoso tower is as much a product of a different regulatory culture as a different design culture. It’s hard to get the look without the rules.