A five-story residential building made of Cross-Laminated Timber (CLT) massive wood

Architects impression of the Walden 48 timber multi-story building in Berlin, Germany

Located in the heart of Berlin, Walden 48 comprises 40 apartments and is built to high environmental standards. Cross-Laminated Timber was chosen as the construction material for structural walls and floors. Wood helps to improve energy efficiency and significantly reduces construction time as the shell can be completely built in under two months.

The challenge

Walden 48 building has been designed to meet high sustainability standards, making thermal insulation a key challenge for the designers. Also, the busy location of the building and the noise coming from the side streets made sound insulation another concern for the architects.

In addition, high fire safety standards were difficult to meet, due to the lack of internationally-approved solutions for firestop in wood. Every pipe and cable penetration in a fire-rated wall must be sealed with firestop products rated for 90 minutes. Wood is not a standardized material like concrete which makes each application different. For that, finding a firestop solution to meet these requirements was a key challenge for the M&E planners and firestop engineers.

Our solution

A Hilti firestop expert was contacted by the M&E planners after a Hilti presentation on firestop in wood during the Firestop Academy in Berlin. From an early phase, the firestop expert was in contact with the planners to craft a firestopping solution for waste water, fresh water and heating pipes, as well as electric cables going through a single opening in a 90-minute fire-rated wall.  

Based on official fire tests conducted by Hilti, the expert designed a project-based solution and provide an engineering judgement. Hilti CFS-BL P firestop blocks were specified as a solution to seal the large opening with mixed penetrations.

CFS-BL P firestop blocks come with a broad range of approvals for mixed penetrations, as well as being fast and easy-to-install. As a preformed and ready-to-use product it also helps reduce overall construction time. Also, it provides high acoustic insulation and carries the Hilti Clean-Tec logo, which stands for more environmentally-friendly Hilti products.

I am so glad that I attended your presentation at the Firestop Academy in Berlin. It was the first time that I saw a possible solution for the project

Gaby Kühn
M&E planner
Syrius Ingenieur/-innengemeinschaft GmbH


  • Image of a Hilti CFS-BL P firestop block

    CFS-BL P firestop block

    Preformed firestop blocks for sealing cable penetrations

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