TWO 21 METRE-TALL wooden towers have recently been erected in the Royal National City Park in Stockholm – one in Frescati and one in Värtan. Their function is to vent air from the Norra Länken road tunnel, which is set to open in late 2014/early 2015. The towers were designed by Rundquist Arkitekter and rise up like two giant cigars. When the sun hits them, they gleam like gold.
Both take the form of a twisted triangle and are built in sections cut from cross laminated timber (CLT) sheets using a CNC milling machine. All the uniquely shaped sections are then screwed together in a total of 117 bands rising up to 20 metres. Each band comprises six parts, so each tower is made up of 702 unique elements, all cut from the CLT sheet. It took around 6,000 screws at 400 mm long to fix these in place. Six tie-rods inside the structure hold the tower together. These are sprung so that the stays can follow the movements in the tower.
Western red cedar shingles clad the towers. The shingles were considered the only facade material able to do justice to the towers’ uniquely billowing shape. The towers were manufactured and constructed by Martinsons.«