Complicated project behind an ancient façade

In November 2017, a devastating fire broke out in a property on Biblioteksgatan in central Stockholm, Sweden. The interior of a historic property was completely destroyed, while thankfully the stone façade, inspired by medieval architecture, remained. Work has now begun to build a new property inside the unique 120-year-old façade. The property owner, Hufvudstaden, has hired Polygon Sweden as the environmental coordinator and an advisor in moisture safety in this significant and spectacular project.

Management of contaminated soil

The autumn of 2019 witnessed the commencement of work to remove the damaged interior materials, including some demolition of fire-damaged elements which were beyond repair.

"A natural consequence of extinguishing a fire is the creation of chemicals. This, together with 120 years of use affected the ground," explains Maria Nordberg, Head of Environmental Services at Polygon Sweden.

"The property owner specified that the finished building should conform to the environmental and sustainability standard BREEAM. It was my role, in consultation with the client's own environmental coordinator, to ensure those standards were met through the project.”

She continues “Among other things, we needed to handle 9,500 tons of soil, five tons at a time, that were excavated from the basement floor, and ensure it was safe and recycled appropriately”.

Challenging logistics

The logistical challenges associated with the project are also considerable, with heavy machinery needed for both excavation and reconstruction. The only way in and out of the building is via the open roof,  six floors up. So, to gain access, large cranes are used; a challenge in itself in the area of the city dominated by narrow streets.

Moisture safety through the construction process

“Step one in a construction process is to create a moisture safety document describing how moisture safety is to be ensured in the entire construction process by all stakeholders”, explains Niclas Prytz, Moisture Consultant at Polygon Sweden.

Moisture damage risk is identified

In this project the client retains a great deal of responsibility for the project and is the signatory for agreements with various subcontractors.

The project has about 30-40 different contractors, and some of their activities require moisture and water management, including;

• Tiling – working with waterproofing. 
• Frames - the right thickness and the right concrete to avoid moisture damage.
• Roofs and terraces – waterproofing.
• Floors - wooden floors must be glued.

"These specific activties are monitored a little more carefully, with additional requirements for, among other things, the moisture safety documentation," says Niclas.

"An example of a challenge from a humidity point of view is that production takes place without special weather protection. This requires, among other things, special constructions and water drainage as well as special concrete qualities for later drying." he continues.

What happens now?

“In consultation with the property owner, a moisture safety plan is now being developed and we expect each subcontractor to work accordingly. Everyone must understand what is expected of them. After that, construction begins, from the bottom up, floor by floor” says Niclas.

By 2023, the building is expected to welcome its new tenants, offering 4,700m² of modern office accommodation, and 900m² sqm of housing. We hope that the new ‘castle’ will retain its stately position in the city for at least another 120 years.