Recycling stone wool and building sustainably

Conscious construction becomes a reality in Leipzig

The challenge

In Leipzig-Grünau, the housing cooperative WBG Kontakt e.G. is actively refurbishing a large building that was initially erected in 1984 as a prefabricated slab construction. The goal of the project is to transform the space into a modern, energy efficient residential complex – and to do so within a construction period of about two years. To stay true to the sustainable focus of the project, their aim is to significantly limit the amount of construction waste to landfill.

Developed in the early 1970s by the Deutsche Bauakademie and the Technical University of Dresden, the WBS 70 housing series was the most commonly used prefabricated building system in the former GDR (East Germany). The residential complex in Leipzig is no exception. Known as ‘An der Kotsche’, the complex consisted of 246 flats in five WBS 70 buildings, grouped around a common inner courtyard. When the core refurbishment is complete, more than two hundred one- to five-room flats will be available for members of the housing cooperative.

The refurbishment also strives to ensure more comfort for residents by merging individual flats, optimising floor plans, adding balconies or enlarging existing balconies and creating bathrooms with windows to ensure daylight. Improving the energy efficiency of the complex is an important aspect of these enhancements – and this is where stone wool from ROCKWOOL plays a vital role.

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Leipzig, Germany

Project location

Leipzig-Grünau
Germany

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The solution

WBG Kontakt e.G. spent time researching and selecting the best possible building materials for the refurbishment, carefully considering the need for contemporary heat and sound insulation that also improved fire safety and boosted the long-term value of the complex.

To improve energy efficiency, they chose an ETICS system based on 100 percent non-combustible stone wool. The insulation core – Coverrock II – was supplied by Deutsche ROCKWOOL. The interior ventilation systems were equipped with heat recovery.

“This is an important aspect for us,” explains Uwe Rasch, technical director of WBG Kontakt e.G. “After all, the future tenants should be guaranteed favourable rents compared to their level of comfort.”

Sustainable building and insulation choices

Making conscious choices was also important for the housing cooperative.

“We feel a special obligation to build sustainably,” explains Uwe Rasch. “Just as we plant a tree for every child born to a family occupying one of our flats, we also want to show that we are living up to our social and ecological responsibility when refurbishing. Nowadays, younger prospective buyers of flats in particular explicitly ask how and with what materials the building was constructed.”

Hardy Frellstedt from Baureparaturen Leipzig West GmbH, a long-standing partner of WBG Kontakt e.G., supported his client's decision in favour of a composite thermal insulation system based on stone wool from ROCKWOOL, approving of the added offer of a functioning recycling system.

“The building site waste is returned to a ROCKWOOL factory via the Rockcycle system and recycled there to produce new insulation,” he says. "We think that's important.”

ROCKCYCLE

ROCKWOOL’s stone wool is fully recyclable, and products made with it are easily disassembled and separated. The company offers recycling services that involves collecting unused cutaways from stone wool products as well as taking back disassembled stone wool. As a result, ROCKWOOL helps their customers to reduce their waste-to-landfill. Offering recycling services in 14 countries, ROCKWOOL expects to offer the service in 30 countries by 2030.

ROCKWOOL’s other circular initiatives

ETICS expertise

From October 2019 to September 2020, an average of 15 employees from Baureparaturen Leipzig West GmbH, known as BRW for short, were on the building site to insulate and design the façades. The team from BRW have worked with stone wool insulation for 20 years, and are considered experts in the field.

“The number of enquiries for a design with stone wool is growing rapidly, especially in recent years,” confirms Hardy Frellstedt. “You can already say that the trend is more and more towards stone wool and away from polystyrene – also due to the fact that environmental aspects and preventive fire protection play an increasingly important role for building owners. We refurbish a lot of schools in particular, and almost all of them are insulated with stone wool. Builders and those renovating large residential buildings are also predominantly asking for systems with stone wool cores in their tenders."

As an important part of the ETICS applied to the façades of ‘An der Kotsche’, BRW used Coverrock II from ROCKWOOL, a non-combustible insulation board based on stone wool. Thanks to a highly compressed top layer, it ensures excellent plaster adhesion and facilitates dowelling. Around 12,000 m² of Coverrock II was delivered directly to the construction site. During large renovations such as this one, between five and ten percent of the insulation material remains as unworkable cutaway pieces after the insulation boards have been cut to size.

“It's a shame if you just drive the cutaways to the landfill,” says Frellstedt. “Even if stone wool is not harmful to the environment…even if it's just lying there, it makes little sense not to reuse so much valuable insulation material.”

Stone wool – Insulation material of choice

The first completely renovated apartments were ready for their happy tenants in October 2020, and the construction work will be fully completed in the near future.

“The planners as well as all the builders are very passionate about this project,” says Uwe Rasch. “That is why we succeed in proving that it is possible to develop a very modern residential quarter from an old prefabricated building, designed to meet the needs of senior citizens and larger families alike.”

As for Frellstedt, he and his team remain loyal advocates of stone wool when it comes to future proofing a building.

“It remains the insulation material trusted not only by us but also by most of our customers,” says Frellstedt. “It's a material that has proven itself for decades and is demonstrably durable, robust and not harmful to the environment. That's why stone wool fits into our times, when many more people than before are thinking about how to use natural resources and protect the environment.”

Recycling towards a more sustainable future

By cooperating with DEUTSCHE ROCKWOOL, the amount of construction cutaways that ended up in the landfilled was significantly reduced. In fact, the construction site cutaways were removed and completely recycled as part of the Rockcycle service.

“Rockcycle is a great thing. As a processor, you are the one who has to take care of the disposal of the insulation cutaways and this is becoming more and more difficult and expensive because not all landfills accept everything and their fees are constantly being increased,” explains Frellstedt. “You have to take this into account and the clients are amazed at the high costs for the disposal of basically intact material. With Rockcycle, you do something good for the environment, the costs are kept within limits and the effort is manageable. On large construction sites like ‘An der Kotsche’, we simply fill the big bags on the construction site and make them available for collection. When insulation boards are delivered, the cutaways go back to the factory in the same truck, where the material is used again for the production of new stone wool.”

Circularity at ROCKWOOL Group