Casting off

Origin story: Wohnregal, Berlin

Marc Frohn recasts an industrial prefab system as flexible housing for modern lifestyles.

It seems like there’s an inherent contradiction when it comes to prefabricated housing. On the one hand, it has traditionally been based around a standardised plan, with the wall as the basic unit. But at the same time, there’s no single way in which people want to inhabit spaces and the ways we want to live are getting ever broader. This is the challenge we explored at Wohnregal, a six-storey building of apartments and workspaces in the Moabit district of Berlin. How could we rethink prefabrication, exploiting benefits such as cost savings and shorter construction timelines, but make it more relevant to current lifestyles?

In Berlin, we have a long history of prefabrication, particularly in the east. We visited several factories in the early stages of the project – some of them were revamped East German prefabrication facilities, originally built for massive housing projects in the 1970s and 80s. After a little research, we discovered a modular system for warehouses, based not on walls but on interconnecting precast-concrete beams, columns and slabs. It’s a system that has been optimised from an engineering and efficiency point of view – to an extent that an architect would never usually consider.

It appealed to us because warehouses are based on the very idea of flexibility, with open spaces that can be adapted to new uses. The crucial component of the system is the double-T slab – a flat concrete element with two 300mm-deep downstands, designed for long-span construction. With this system we could span the 12m depth of the site very efficiently, giving us complete flexibility over the floorplans.

All internal walls are plasterboard and have the services channelled through them, so the possible variations are almost endless. We didn’t soften the visual quality of the concrete at all – it’s the same finish you would get in industrial construction. We also kept the rough joints you would get in a warehouse, with 2.5cm tolerances, which is unheard of in residential architecture. But actually it creates a curious aesthetic. Within the apartments, if you look towards the facade, you see huge gaps between the columns and beams.

You can’t see the actual connections, so these 5 or 10-tonne elements appear to contradict their weight, as if gravity doesn’t apply. To me, it is an unexpected discovery: you would never have designed it this way if you were using a conventional building process. It would have seemed odd to completely negate this structure by hiding it behind a facade, so we gave the east and west elevations a curtain wall of full-height, triple-glazed sliding doors.

In the hot Berlin summers, these can be opened on both sides, drawing in fresh air and turning  the interior space into a kind of loggia. And with the 2.9m ceiling heights, you get the sense of quite a spacious interior. The glazing also allows light to pierce the rough structural joints behind, adding to the sense that the concrete is floating.

Berlin is an expensive city to build in, but the construction costs of this development compare favourably with the city’s main public housing agencies. Currently, Wohnregal provides a mix of apartments and workspaces, two per floor ranging from 35m2 to 110m2. But of course, this can change at any time.

This building provides longevity and flexibility, which is critical in a circular economy, and because the concrete is mechanically connected you can separate everything by material, which is also useful. No one knows what our requirements are going to be in a generation and a half, so we need structures like this, capable of being reappropriated in ways that aren’t yet clear.

Marc Frohn is a partner at FAR frohn&rojas in Berlin

Photos David von Becker; Guy Wenborne