Thinking Holistically – Green Building at HOCHTIEF: maxCologne, a quality-certified project

As an international construction services provider, HOCHTIEF offers a broad range of services to ensure that buildings are designed, planned, constructed, and operated in a sustainable manner and in accordance with the highest standards of quality. Sustainability criteria are an acknowledged factor in cost-effectiveness. That is because buildings that meet strict ecological requirements are also economical. Production costs may be slightly higher than with conventionally realized projects, but this is offset by the lasting lower operating costs achieved throughout a building’s service life by means of improved energy efficiency. Tenants also appreciate the potential for cost savings such buildings offer and their positive effect on the interior climate. This is reflected by higher rental rates and higher rental income. Sustainable properties also generally have a high resale value. So green building pays off for all concerned: from project developers and construction contractors to those who own and operate such properties, and also, of course, those who occupy or use them.

One current example of this kind of holistic approach, with a concept oriented to a property’s entire lifecycle, is the maxCologne project in Cologne, which is being developed and realized by HOCHTIEF.

Since March 2010 the buildings, which date from 1969 and 1978, are being refurbished to new-build standard. In the period up to fall 2012, a total area of 46,000 sq meters of high-grade and flexible office and catering space is being created, including a 22-story high-rise and the terraced 11-floor “Rheinetagen” building. The maxCologne complex is in a prominent position directly on the Rhine River, looking straight across to Cologne Cathedral and the Old Town district. The property was sold even before construction commenced.

In revitalizing this structure, HOCHTIEF’s project development team is observing the principles of sustainability, in particular with respect to technical standards and energy efficiency. Saving energy during construction and operation is the prime imperative. In addition, it is intended that the maxCologne complex should serve to upgrade its surroundings and the overall location and at the same time blend in ideally with the neighborhood. Extensive demolition measures are creating a public area offering fresh vistas. The catering zone that will be created on the ground floor will also be open to the public. At the invitation of HOCHTIEF, the jury that judged the contest on the new design of the facade included representatives of the Cologne municipal administration.

The redesigned facade gives the building an attractive and distinctive exterior, which also makes for optimum functionality in relation to the ground plan. The concept provides for a horizontally structured glass facade. The single-pitch roof topping the 11-story block gives it a dynamic appearance. In addition, on the top seven floors, there are large terraces facing the Rhine. Inside, flexible ground plans and movable partition walls permit varied forms of space division in line with user requirements.

Demolition work began in March 2010. Next, the two office buildings were gutted and the facade was removed. Summer 2010 saw the start of special foundation works to ensure structural stability and the commencement of the shell works, which are being executed by the HOCHTIEF construction experts. The previously visible concrete stairwells on the outer south and north sides of the high-rise were integrated into an enclosing structure, thus creating additional office space. The enlarged facade surface allows more light to enter the individual building levels. From the stairwells, which now are located centrally inside the building, quick access is possible to all areas of the floor.

The materials and components used in this refurbishment and upgrading project are eco-friendly. Since this is a revitalization of an existing building and large parts of the old load-bearing concrete structure are preserved, the amount of “gray energy” required – that is, the total amount of energy required to create a product – is considerably lower than in a new building of similar size.

The energy concept for maxCologne focuses above all on reducing the consumption of primary energy and on more efficient energy utilization. Most of the energy for the complex is obtained from renewable resources: Groundwater is raised via two wells and used for climate control in the offices by means of heating/cooling ceilings.

The new twin-shell facade consists of a triple-glazed inner shell and a curtain-type outer shell. This helps to save energy. The sun-shielding can be adjusted manually and in line with individual requirements. Since the shielding is installed inside the twin-shell facade in both buildings, it can be used even in strong wind.

With maxCologne, HOCHTIEF is aiming for the Gold Certificate of the German Sustainable Building Council (DGNB). In February 2010, it was already awarded pre-certification in gold, in recognition of the project’s functional, technical, and process quality. This means that even before it has been completed, the ecological, socio-cultural, and economic quality of the project has been acknowledged. These are factors that the occupants will be able to discover for themselves from fall 2012 onwards.