In Frankfurt, two four-storey residential buildings are currently being refurbished. Two minimally invasive refurbishment concepts are being tested that are based on multifunctional window modules and insulation elements. Both systems are industrially prefabricated and can integrate various building services functions. The primary refurbishment measures can be carried out from outside.
The new renovation concept is the insulation of integrated ventilation ducts, and supply through the window openings. “We deliberately opted against large-scale, storey-tall façade constructions in order to limit the effort spent on measurement, construction and construction logistics,” says Dr. Michael Krause, project manager at the Fraunhofer Institute for Building Physics (IBP) in Kassel. Using a renovation plan with smaller-scale elements, the researchers hope for easier handling, improved flexibility and an easier integration with traditional construction processes.
As part of the EnOB research project “Development of prefabricated, multifunctional systems for the renovation of residential buildings (Prefab)”, a window module was developed by Fraunhofer IBP that already comes with a window frame connector, an insulating material rim for covering the façade in the window area, and a so-called technology module to house the building services systems. This module, which is located beneath the indoor windowsill, can also serve as an interface for the supply systems in the façade and for the room-side installations. The system was further developed as part of the EU project “RetroKit Toolboxes for systemic retrofitting”. It is now being tested with the renovation of the four-storey residential buildings in Frankfurt, as well as a similar system from the Fraunhofer Institute for Solar Energy Systems (ISE).
Testing the system in multi-family dwellings built in the 1950s
Windows are the technically most demanding components of the building envelope. This applies not only to their installation but also to existing openings in the building. This is where the most planning and construction errors occur during renovation. “Shifting the demanding and thus error-prone installation work to the prefabrication stage under workshop conditions significantly increases the quality of the execution and enables synergy effects to be utilised,” Mr Krause notes. This concept could replace the laborious renovation methods traditionally used for multi-storey apartment buildings from the 1950s to the 1970s.
Testing is currently underway in two multi-family residential buildings owned by ABG Holding, built in 1954. As is, they currently require 175 kilowatt-hours per square metre of living space for heating and hot water. In addition to the new thermal insulation, the buildings are being fitted with ventilation systems. With the air inlet/outlet system, the air quality and noise situation should improve significantly in buildings situated near heavy traffic.
The innovative solutions as adapted to the projects and developed by the two Fraunhofer Institutes IBP and ISE will be employed for testing. Airflow takes place entirely within the two-layer insulation system. The new windows are set in front of the existing façade in order to prevent thermal bridging and to establish a connection to the ventilation system. This way, the inhabited building can benefit from energy efficiency improvements with minimal disruptions to tenants and without using up extra space inside the apartments.
The entirely prefabricated window module, originally developed during the research project EnOB Prefab, is being used in the buildings in Frankfurt in an adapted form for construction-related and logistical reasons.
Air and plumbing lines in the façade insulation
A load-bearing system available on the market that is used to install the window in front of the wall is installed from the outside, along with a prefabricated air inlet and outlet element specially made for the project. The insulation for the remaining façade area between the already installed windows is then completed. The air ducts are located in the façade insulation, within prefabricated insulating panels with fitting recesses.
Originally, two different systems were planned for the airflow inside the façade: the system for House 1 as developed by Fraunhofer IBP, and a similar system for House 3 from Fraunhofer ISE. However, both systems are based on the combustible insulation material EPS (expanded polystyrene) and do not yet have their general technical approvals. The two residential buildings are legally classified as building class 4 with regard to fire safety laws, which entails higher fire protection requirements. The approval cost on an individual case basis, with the addition of appropriate fire dampers and a large-scale fire test, was beyond the financial and temporal limits of the renovation project. Therefore, a two-layer insulation system made of non-flammable mineral wool is now being realised with a ventilation guide consisting of an inserted, folded spiral-seam pipe.