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The “Holzrotonda” in Rotenburg/Wümme was designed by Wirth Architekten according to cradle-to-cradle principles.

BLACKPRINT: In Rotenburg/Wümme—right in the heart of northern Germany—you’ve completed the so-called “Holzrotonda.” The building is defined by its narrow base and a first floor that cantilevers all around. What advantages does this unconventional plan offer, and how did you arrive at the solution?

Jan Wirth: A typical subdivision of single-family homes doesn’t exactly stand for progressive thinking. But our client is a very open-minded person, which gave us the opportunity to test as much as possible. If you mentally step back from the immediate context, you suddenly notice many qualities: the forest edge, wide views over the landscape, the open sky. At the same time, we realised the local development plan did not strictly require a ground-hugging construction. That gave us freedom—especially for the upper floor. The result is a house that gently lifts itself above the neighbourhood level and opens up new perspectives on the flat northern landscape.

BLACKPRINT: And of course there’s the “side effect” of using very little land…

Jan Wirth: Yes, that was central. A conventional house touches the ground with its ground floor and, in many cases, extends into it with a basement. As a counter-strategy, we reduced the enclosed space on the ground floor to a minimum—essentially a central spiral stair, a cloakroom, a guest WC, and a storage room. The house therefore uses far less land than a standard home—and in two ways. First, the area beneath the house is not sealed; grass actually grows there. Second, the cantilever creates “covered” terrace and parking areas that are sufficiently dry and therefore don’t need to be sealed either. We also significantly reduced the Holzrotonda’s CO₂ footprint: the small bearing area allowed us to minimise both the concrete and the insulation required.

BLACKPRINT: In the end, you created a prototype—a model for land use…

Jan Wirth: In a sense, yes. But fundamentally we remain skeptical about the detached house. Compared to compact urban housing, it still consumes a lot of land. That said, if you build in a consistently resource-conscious way—with a high timber content, excellent insulation, photovoltaics, a heat pump, and very low energy demand overall—you can, to some extent, overlook the higher land consumption. And you can’t seem to wish away people’s desire for a single-family home. In that respect, it can be meaningful to accommodate this anthropological constant as gently as possible—and rethink the detached house.

BLACKPRINT: Another key aspect of the project was implementing cradle-to-cradle principles. How did you achieve that?

Jan Wirth: The Holzrotonda is essentially a dry, timber “box” resting on a mini concrete plinth, built entirely of screwed timber components. We opted for a very restrained interior without additional service layers. We also completely avoided composite materials and even omitted the gypsum plasterboards that are typically screwed over OSB sheathing. The only exception is the plinth—which, as noted, is radically reduced in size. In principle, you could unscrew the house like a kit and reassemble it somewhere else.

BLACKPRINT: And the exterior?

Jan Wirth: There, too, we deliberately avoided the local fashion for heavy fired brick cladding. Instead, we looked to regional building types and arrived at a façade of corrugated fiber-cement panels—similar to the claddings found on extensions to nearby farmhouses.

BLACKPRINT: How firmly established is the demand for “sustainable architecture” now? What are you experiencing?

Jan Wirth: It feels like we’re in a phase of searching. Many approaches are being tested—and some fail. In Bremen, for example, there was a time when all public buildings were planned as passive houses; then that target was dropped. Even so, among private clients a lot has changed in recent years: sustainability is a given. It’s now taken for granted that materials should be ecological and that as much as possible should be reused. But when it comes to the big CO₂ emitters—public buildings or investor-driven developments—we still have a long road ahead to shift mindsets there as well.

BLACKPRINT: Your projects aren’t just sustainable and functional—they’re also aesthetically compelling. What’s your approach?

Jan Wirth: Generally, we sense that many practices design primarily for a professional audience. It’s often about executing a rigorous idea that remains as reduced and legible as possible. Our approach goes further: we also want to consider a broader public’s taste—without lapsing into arbitrariness. We don’t lose sight of the professional audience, but we care about the atmosphere our buildings create in the city. A useful test is to imagine yourself sitting at a café in front of a building, looking at it for a while, and then asking whether the design fits the context—how it interacts with its surroundings, and what architectural references it makes in terms of scale, materiality, or grain. Much of that isn’t purely rational. It’s about intuition: what images and references do you carry with you? What do you connect to in order to create something that sits convincingly in its place?

BLACKPRINT: Housing is a core focus of your office. A strong example is the new Speicherquartier in Bremen-Vegesack. What was your planning objective?

Jan Wirth: With the Speicherquartier, we were fortunate to enter the project via the urban design competition. That meant we could help shape a new urban piece for Bremen-Vegesack right from the start—approaching the building “from the outside.” In parallel, we had to consider which building types and uses to allow inside. What I find particularly appealing in such urban projects is subsidised housing. It’s not about luxurious living but about the question: what constitutes good, affordable architecture? That was also the case with the Kaffeequartier in Bremen—two buildings totaling 80 subsidised apartments. The brief there was to use the floor area optimally to limit rents and comply with maximum sizes for subsidized housing. Our goal, therefore, was to reduce apartment sizes as far as feasible while designing the plans so efficiently that the spatial impression remains airy, not cramped. The solution is a central sanitary core around which all other functions are arranged in a ring. This generates a generous, open sense of space—quite unlike conventional compartmentalisation into separate rooms. Where needed, sliding elements can subdivide the layout—for instance, for families with two children or to create a separate dressing area.

BLACKPRINT: I don’t know another architecture office run by two siblings. Isn’t conflict inevitable?

Jan Wirth: The setup came about naturally—probably because we spent time tinkering around our parents’ smallholding and discovered a shared passion for building. After school, I studied in Rome and Paris; my brother was in Berlin and also in Paris. We initially looked for more partners to found a practice with, but that went nowhere—few architects set up on their own these days. So we decided to do it together. Of course there’s the occasional friction between siblings. But many things move surprisingly fast because we’ve communicated on the same wavelength for years. Sometimes a few word fragments are enough to reach a decision. You notice it especially when talking to others—and suddenly you have to explain yourself at length. In our office it’s already clear what’s meant while others are still trying to grasp the direction. It definitely has pros and cons.

BLACKPRINT: How does being based in Bremen shape your work—is there a specifically “northern German” approach?

Jan Wirth: Good question. Our trajectory was probably only possible in Bremen. There’s a remarkable density of terraced houses in urban neighbourhoods—the classic Bremen house in all its variants. We were able to start by remodeling small houses on tight budgets—and we repeatedly met progressive clients open to new ideas. That led to early projects that could be published and got us noticed. Only then came competitions, which lead to larger commissions. But it often takes years from a competition win to a completed, publishable project. In that sense, Bremen—compact and fine-grained—was the perfect launchpad for us.

BLACKPRINT: Which developments are you observing in architecture right now—and which do you consider especially important?

Jan Wirth: Beyond sustainability, we’re currently fascinated by the use of AI. Normally, for each new project, we study a broad set of references and develop our own design from there. If you delegate parts of that process to AI, the result often comes surprisingly close to what we had in mind. Of course, implementation quickly reveals where ideas won’t work—say, an out-of-place marble frieze. But new perspectives open up, and we become aware of our own cognitive boundaries. What that will ultimately mean for our work is still unclear. But AI may well take over repetitive tasks and free up more time for true design thinking and spatial quality. A nice example appeared at the Biennale: an AI-generated apartment plan tested in 200 variants. Sure, a human can do that too—over two weeks. AI does it in 20 seconds, allowing us to test and compare options at speed.