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19. March 2026

Urban Living: Molitor and Rheinhessen Sparkasse Develop "Cosmo"

Through the Cosmo project, J. Molitor Immobilien GmbH and Rheinhessen Sparkasse are planning a striking new residential and commercial building on Saarstraße in Mainz.

An urban complex comprising a total of approximately 66 apartments and about 514 square meters of office and medical practice space is to be built on the former site of the Karell car dealership. The new head of the Department of Building, Ludwig Holle, presented the building permit for this major project during a press conference.

Living and Working in a Central Location 

The housing offering focuses on modern two- and three-bedroom apartments, supplemented by one- and four-bedroom units. Sizes range from approximately 31 to approximately 91 square meters. In addition to the apartments, space for offices and medical practices is planned for the ground floor. The project developers are targeting urban professionals who will benefit from the convenient location on Saarstraße and the immediate proximity to Mainz Central Station. “It is precisely the proximity to the university, the university hospital, the new biotech campus, media and research institutions, the companies in Mainz’s Oberstadt district, and the main train station that makes this location attractive,” says Molitor Managing Director Tina Badrot. Sales of the condominiums are scheduled to begin at the end of March. “Prospective buyers can register their interest starting now,” said Tina Badrot. Construction is estimated to take approximately 18 to 24 months, with work scheduled to begin this summer.

Urban Development

“The Cosmo building will allow us to continue developing the city’s entrance along Saarstraße,” says Ludwig Holle, Mainz’s new head of the Department of Construction. “This project will create a property that provides much-needed urban housing even within a compact space.” At the same time, thanks to its location and the continuation of development along Saarstraße, it will further shape the city’s character. Furthermore, the building has the endorsement of the City of Mainz’s Planning and Design Advisory Board, which was also involved in the process during the previous planning phase.

The complex was designed by the Mainz-based architectural firm mann + schneberger BDA, whose high-caliber designs are regularly honored by inclusion in the select lineup of Architecture Day. “It is important to us to create a building with Cosmo that confidently positions itself within the urban landscape while simultaneously establishing connections to the existing surroundings,” explains architect Ludwig Mann. Thus, the new building deliberately enters into a design dialogue with the Catholic University across the street and, together with it, forms a striking “city gate” at the entrance to downtown. The clear grid pattern of the facades echoes elements of the university’s architecture, while a rounded entrance area adds a striking accent. “The brick facade at the base, striking color accents, and generous window areas give the complex an urban, timeless appearance,” says Ludwig Mann.

Quality of Living Despite the Traffic Situation

Special attention has been paid to quality of living: Soundproof “Hafencity windows” are used facing Saarstraße. Many apartments feature balconies that are glazed and can be enclosed in winter to create sunroom-style balconies. On the penthouse level, penthouse apartments with rooftop terraces are also being built. On the rear side of the building, facing the art academy and green space, large window fronts open up to offer views.

Sustainable Energy Concept

Cosmo is committed to a forward-looking energy supply: geothermal energy enables heating in the winter and passive cooling in the summer. The long-term goal is to provide residents with stable and comparatively low energy costs. “With the Cosmo project, we are joining forces with J. Molitor Immobilien GmbH to send a strong signal for sustainable, urban living in Mainz. Through innovative energy concepts such as geothermal energy, photovoltaics, and green roofs, we are not only creating a modern home but also contributing to climate protection. Rheinhessen Sparkasse supports prospective buyers with expert financing and personalized advice—for a high quality of life and future-proof living in the region,” said Dirk Scherrer, Division Director of Digitalization / Digital Sales / Sustainability at Rheinhessen Sparkasse.

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