ELS60

Energy efficiency façade renovation with customised refurbishment window sashes

The façade of an eleven-storey office block at 60-62 Eschersheimer Landstrasse in Frankfurt is being renovated during ongoing operations. A project specific renovation sash from WICONA and Bonik Sustainable Facade (BSF), combining energy efficiency and design, is being used for this purpose and is particularly sustainable thanks to a closed aluminium circular economy.

Ensuring the future viability of the location

The ELS60 high-rise building built in the 1960s stands on one of the busiest transport axes in central Frankfurt and contains both office spaces and a food market on the ground floor. In order to ensure the attractiveness and future viability of the location, the owner, Ali Selmi Grundstücksgesellschaft bR, decided to renovate the ageing façade. Architect Jakob Meves, representing the owner, explained: "We did not want a long period with the building vacant but went for a solution that would bring the façade technically up to date, lower energy costs, save resources and at the same time enhance the look of the building – and do this without interrupting ongoing office operations." Bonik Sustainable Facade (BSF) as the general contractor was therefore commissioned with planning and implementing the entire renovation operations, including coordinating all the consultants and trades.

Targeted revitalisation instead of replacing the whole façade

The building's existing windows showed various types of damage such as hardened and leaking seals, resulting in energy losses and reduced sound insulation, and allowing rainwater ingress in places. The inside also overheated in summer due to a lack of effective solar shading. Instead of a complete façade replacement – this would have been very costly and have necessitated around eight months of additional construction time as well as a loss of rent and alternative rentals – a decision was made in favour of selective revitalisation of the windows. During a full inventory involving opening the structural elements, the installed systems and series, mountings and structural concepts were all recorded in detail and the existing windows and frame structures as well as insulation were thoroughly checked. This demonstrated that a two-layer mineral fibre insulation was already present in the opaque areas – allowing a better U-value to be considered for the renovation planning than had been previously anticipated.

"Minimally invasive" intervention for excellent energy-efficient performance

Based on the inventory and the client's requirements, BSF along with WICONA developed a project specific renovation window sash using the WICLINE 60 system. The idea is that the existing and completely sound frame structure will remain in the building. Only the window sashes will be exchanged – fitted with hardware and seals exactly matched to the frames, as well as energy-efficient triple glazing. The concept will be supplemented with external solar shading using ZIP screens equipped with a control system. This will reduce the U-value from ≥ 1.7 to ≤ 1.1 W/m²K and the heating energy loss by around 35%. In addition, internal noise will fall by around 5% and the energy input in summer by around 87% due to the shading. Planner Christian Bonik from BSF explained: "We will be achieving almost the same effect as a new façade but with minimally invasive intervention – no demolition, no long down times, and with a clear perspective for the coming decades."

Interventions in sync: logistics during ongoing operations

In order not to disturb ongoing office operations during the works, BSF in cooperation with Heidersberger Fassadenbau developed an ingenious logistics concept. As it was not possible to set up storage areas and larger construction site facilities due to the limited space in the inner city location, the new pre-glazed windows are supplied just-in-time, transported to the floors by lift and replaced one office at a time in a schedule agreed with the users. "We organise dismantling and installation in such a way that the rental spaces are affected for as short a time as possible. The prefabrication of the window sashes ensures rapid replacement – clean, quiet and quick", explained Udo Wüller, managing director at Heidersberger Fassadenbau.

A true circular economy with aluminium

Besides its cost effectiveness and implementation during ongoing operations, the project impresses with its consistently sustainable approach. One of the client's requirements was to make the best use of the existing structural fabric in order to retain embodied energy and conserve resources. After being removed, the existing windows were dismantled on site and separated into the different end-of-life materials aluminium, glass and seals. WICONA's circularity team supervised the planning and logistics along with Heidersberger Fassadenbau, and ensured that every step was documented and remained clear and comprehensible. The end-of-life aluminium is recycled in the Hydro works in Dormagen – and ultimately used to produce new profiles of the sustainable Hydro CIRCAL alloy. The WICONA renovation windows used in the project and manufactured by Heidersberger consist of a minimum of 75% post-consumer material and have a very low CO2 footprint of only 1.9 kilogrammes CO₂ per kilogramme aluminium.

Optimum combination of technology, cost effectiveness and sustainability

The ELS60 project impressively demonstrates how existing buildings in need of renovation can be brought up to date technically, economically and sustainably by means of accurate analysis, customised renovation window sashes and a true circular economy. The client saves investment costs and loss of rent, the user benefits from increased comfort and the cityscape undergoes a visible improvement.