Low-tech for high energy

The client was looking for an impressive new building, a place to house modern offices and with a strong focus on sustainability. At the same time, the new headquarters of the Stiftung Unionhilfswerk Berlin shouldn’t be pretentious. The challenge was met with a sustainable, low-tech concept.

A sustainable storage body in Berlin

Baumschlager Eberle Architekten’s Berlin office was faced with the challenge of bringing together various requirements in one place. The result is a high-quality brick building with a total primary energy requirement of only 62.1 kWh/m²a. The right building materials and a low-tech concept made this possible, because technical systems for optimising the energy performance of buildings are often thought of as too short-term: “Technical systems are expensive, require a lot of maintenance, increase life cycle costs and have a high energy demand themselves,” explains Gerd Jäger, co-founder and Managing Director of Baumschlager Eberle Architekten Berlin.

Unionhilfswerk’s new office building therefore exploits the laws of physics and manages to perform with as little technology as possible while maintaining a high level of comfort and optimal room conditions. The thermal mass of the building envelope made of highly insulating Poroton clay blocks plays an important role here.

„The storage capacity of the bricks lasts up to three months. If the wall can still absorb warmth in late autumn, it will last until February“, - Gerd Jäger, Baumschlager Eberle Architekten Berlin

Storing and emitting heat

With its tidy perforated façade, upright window formats and circumferential frames reminiscent of Berlin’s Wilhelminian buildings, the administration building has stood in Berlin Tempelhof since 2021. For the heating and cooling concept of the five-storey office building, the architects used the thermal storage mass of the exterior walls and storey ceilings and optimised the proportion of glazing to reduce heat loss. The windows, which are flush with the exterior façade on the inside, are shaded by the deep reveals when the summer sun is high in the sky. This makes external sun protection almost entirely unnecessary. Night cooling is used via central atriums.

The building only needs to be heated or cooled a few days a year. “The storage capacity of the bricks lasts up to three months. If the wall can still absorb warmth in late autumn, it will last until February,” explains Gerd Jäger. Underfloor heating – supplied by a reversible heat pump in conjunction with a photovoltaic system – can be switched on as required.

A strong presence in the district

For structural reasons, the 42.5 cm thick Poroton block with mineral wool filling was used for the monolithic wall construction. To further increase the thermal insulation, the architects added Poroton-WDF blocks filled with perlite to the construction. In total, this resulted in a 59 cm thick wall construction with an overall U-value of 0.15 W(m²K).

This compact and efficient form allows for a high level of comfort and optimal room conditions inside the building. “We’ve created a building that embodies and makes visible the attitude of the foundation. It strengthens the presence of the Unionhilfswerk in the borough and sets an urban accent through its architecture,” says Gerd Jäger.