A physical building model whose floors had yet to be glued down was the design genesis for the seemingly casually stacked floor plates of Patch22, a seven-story, mixed-use timber structure in Amsterdam by local firm Frantzen et al Architecten. But the concept of pushing the envelope of what’s possible through architecture dates back to 2005, when firm founder Tom Frantzen first began directing the money he spent on design competitions toward development projects.
Four years later, the city of Amsterdam was soliciting proposals that prioritized sustainability for a waterfront site in the industrial Buiksloterham district in North Amsterdam. “This is our chance,” thought Frantzen and his business partner, Claus Oussoren.
And it was. Their concept—a 58,000-square-foot, net-zero energy building composed of a row of townhouses that culminates in a 100-foot-tall tower—was selected, scoring an 8.9 out of 10 on the city’s sustainability evaluation. Earning points were the project's proposed solar panels, graywater recycling system, and a heating system that uses pellet stoves fueled by a timber byproduct. But for Frantzen, Patch22’s real innovation is its structure, a heavy timber frame made from glulam and CLT, with hollow concrete-and-steel floors that allow for flexibility in programming.
On its exterior, Patch22’s broad-faced tower is defined by its skewed floor plates and exposed timber trusses, which visually reinforce the building’s horizontality. Despite appearances, the tower’s primary structure is purely rectangular, a skeleton of timber columns and beams that join at right angles. The projected corner, or “twist” from floor to floor, is achieved by sequentially extending the building’s massive transverse floor beams—measuring 1.5 feet wide, 2.6 feet deep, and approximately 30 feet long—a foot further than its neighbor. The reverse happens on the building's opposite face, creating a parallelogram in plan.
Cantilevered off the main structure are enclosed balconies of variable depths, with glazing to buffer both noise and wind. Structurally, the balconies are stiffened by an exoskeleton of redwood trusses, 8 inches wide and 12 to 20 inches deep, that tie into the floor beams via steel knife plates and a series of bolts.
Moisture was among the biggest challenges when building with exposed trusses, Frantzen says. “[T]he Netherlands are almost never totally dry,” he says. “We have an ideal climate for microorganisms so if you get water inside your structure, the structure will start to rot immediately.” Steel caps completely cover the ends of the diagonal web members where they connect to the top chord. Where they connect to the bottom chord, the steel plate is surface mounted to the lower chord, rather than embedded.
Similarly, where the tops of the twisted story volumes jut out, the architects needed to shed water from the miniature roof decks. They added aluminum trim with a ventilated backing sloped away from the building. The trim was necessary on just one half of the façade length, since the other half transitioned to become recessed below the floor above it, but Frantzen and his team decided to run the trim the full length to reinforce the aesthetic of the disconnected volumes piled atop each other.
Moisture also dictated the coloring of the building. For Patch22's more solid east and west elevations, the architects specified fire-treated Douglas fir that had been pre-weathered. “If you didn’t pre-gray the façade, it wouldn’t gray evenly,” Frantzen says. “You would get black lines.”
Construction of Patch22 began in December 2014 and was completed in March 2016. After that, the individual commercial and residential interiors were fit out. Frantzen’s firm moved into the building and also designed several of the tower’s 31 units, while consulting on the remainder. “We assisted all the buyers but [acted] more like the editor of a magazine,” Frantzen says, revising plans to meet building codes and to maximize functionality—but otherwise remaining hands-off. He adds that the famous 1909 drawing by A.B. Walker showing a New York skyscraper composed of traditional houses was inspirational: “We wanted to give people freedom to design their own villa.”
Patch22’s adaptability and versatility have already been tested—by Frantzen himself. After his wife accepted a job in Denmark, he downsized their original apartment in Patch22, which was half a floor. “We sold part of our apartment, and we kept the smaller part,” he says. They added division walls, rerouted some of the plumbing, and added new electrical meters. “Everything was connected, and then we had a new, but smaller, home. It even had the right house number because we were smart enough to negotiate with the city that we needed extra house numbers in a good order in case the big apartments were split up.”
More than a decade later, Frantzen’s decision to wade into development seems to have paid off: He and Oussoren are constructing a second seven-story building of mass timber, concrete, and steel, on the plot of land immediately adjacent to Patch22. Frantzen believes the increasing visibility of timber structures in Amsterdam, led by Patch22, has paved the way for even higher-profile projects such as Haut, a 240-foot-tall tower designed by Team V Architecture, based in Amsterdam. “That project is a being done by a commercial developer,” he says. “And they would have never, ever dared it without this building being a success.”
Editor's note: This story has been updated since first publication.