Established in 1889 Helsinki’s Korkeasaari Zoo, located on Korkeasaari Island, has animals from Finland and around the world housed in large natural enclosures.

The competition for the design of the ten-meter-high timber tower, presented to students of architecture at Helsinki University of Technology, was organized by the Korkeasaari Zoo in collaboration with Wood Focus Finland.

The load bearing structure consists of 72 long battens, with a section of 60mmx60mm, that are bent and twisted on the site from seven pre-bent types.  Over 600 bolted joints hold the shell structure together.
Having no weather protection the wood is treated with a linen oil-based wood balm with UV-protection.
The free form of Hara’s winning entry, inspired by the natural setting, follows the existing low stone wall and skirts around a small birch grove.

When the drawing of the irregular form proved difficult Hara moulded a plastoline model. Digital images of the model then functioned as a basis for the AutoCAD drawings.
Using the level drawings he constructed a 3D-computer model onto which he ”taped” the curved battens to form the grid shell.
Students at the Wood Studio workshop developed the draft design further by assembling scale models and exploring structural details.

To test if  the pre-bent battens, that form the  basket-like grid shell, tolerated bending and twisting Hara laminated full-scale pieces of the battens. When the laminated timber resisted twisting he resorted to steaming, a traditional method in boat building.
The effect of surface treatment with linen oil-based wood balm on moisture content was determined by moisture tests and the durability of the joints was proved by tension tests.

The tower was erected by an international group of eight students of architecture. With the hot, sunny summer drying up the timber, the duct pipes that were used for steaming proved useful. It took us three months to complete the job.

The Helsinki University of Technology Wood Studio workshop was started by Professor Jan Söderlund in 1994. The course was aimed to contrast the rather pragmatic building technology courses. It is characterised by innovation and artistic approach. The students are selected by an annual student competition and half of them are foreigners.
The department of Architecture now has a new professorship for wood architecture with Professor Georg Grotenfelt running the Wood Studio course.

From the architects’ website:

‘Situated on a cliff-top site eighteen metres above sea level, with spectacular views of the sea and the city of Helsinki, the ten-meter tower is a delicately transparent landmark for Korkeasaari Island. The free form is inspired by its natural setting: it follows the existing low stone wall and skirts around a small birch grove.
The load bearing grid-shell structure consists of 72 glue-lam battens, with timber sections of 60mm x 60mm bent and twisted on site from seven preformed types. Over 600 bolted joints hold the shell structure together. The tower was a HUT Wood Studio project in 2000-2002 and student Ville Hara’s graduation project.’

For more pictures visit the architects’ website: www.avan.to.