The presentation of Construction of Treet: A 14‐storey timber apartment building at the 2016 Interntational Wood Symposium in Vancouver was helmed by Ole Herbrand Kleppe the chief project manager at BOB Eiendomsutvikling AS and Rune Abrahamsen, the CEO of Moelven Limtre. Both firms are in Norway.
Bergen, Kleppe said, is the "capital of rain," which makes wood construction difficult. The site of the Treet project is in the city centreand is part of a revitalized area that is being converted from industrial to residential.
Treet will be a 14-storey timber apartment building and normally the size of a building in the area is capped at nine storeys (the height of a nearby bridge.)
The project's goals were to create a sustainable and cost efficient urban highrise wooden house using industrial processes and prefabrication. The building took inspiration from timber bridges. "Essentially we're taking a timber bridge and putting it upright," Abrahamsen said.
The structural system makes extensive use of glulam and cross laminated timber (CLT) that is sourced from Germany.
The Treet project uses a timber lateral load resisting system, as opposed to a steel frame. It is built on modules stacked up to four levels high and are only connected to the main structure in the lowest module in each stack. Single level modules are in the power storeys.
Glulam carries all the horizontal and vertical loads. Concrete is used as the foundation for modules and adds mass to the structure, which improves dynamic behavior. It also worked as a temporary roof during construction.
"We could have made these slabs of wood, but that would not have been smart," Abrahamsen said.
Durability is a major concern, Abrahamsen said, but "history is on our side," pointing to churches in Norway that are almost 900 years old and are made of wood. Fire was, of course, a concern and timber is not pre-accepted for highrises in Norway. However, Norwegian regulations open up for alternate materials as long as required documentation is produced.
"Timber can burn and in this project the glulam is so thick that we can allow it to burn for 90 minutes without failing," Abrahamsen said.
Earthquakes are not a concern in Bergen, but hurricanes are. After testing, it was determined that residents in the top floors might feel vibrations, but would not be uncomfortable. The assembly procedure was to install a module and then put the load bearing system around the module.
The building has 62 apartments, is 14-storeys tall and has an elevator shaft in CLT, which is 15 storeys high (due to the basement.)
After a break, the seminar continued.
Ole Herbrand Kleppe the chief project manager at BOB Eiendomsutvikling AS and Rune Abrahamsen, the CEO of Moelven Limtre starting going into more detail about the construction of the innovative Treet timber apartment building in Bergen, Norway.
Kleppe said with the project that "the devil is in the details." They found that changing the footprint helped them succeed and that cross laminated timber (CLT) can be used to a high degree of accuracy. They also discovered that using CLT to build an elevator shaft is cost and time efficient.
"The installation of the elevator in a 15 storey shaft was precise and hassle free," Abrahamsen noted. Other lessons included the fact that "the balconies cost more than you get back." He added pilot projects have higher costs and the client's profit on this project was minimal.
Kleppe stressed that development support from Innovation Norway was crucial to realize the project. Abrahamsen said that future tiber highrises will be competitive and that construction time (April 2014 to December 2015) was quicker than a comparable steel and concrete project.
"The sharing of a large building crane between the involved parties worked very well," he added.
This project was possible, Abrahamsen said, because BOB was willing to take some risk. "That's a necessity in a pilot project," he said.
Co-operation between the client, architect, engineers and suppliers throughout the process was crucial, as was political support for the project. Abrahamsen said the project had a high focus on prefabrication, but "we will have an even higher focus on prefabrication next time, particularly on technical installations."
Prefab facades and decks may be considered as alternatives to building modules, he said, and noted that the tolerances of installed glulam and CLT were amazing.
A new spin-off project in Norway is planned for 2017, Abrahamsen said, which will be 17 storeys and 66 metres tall.
The International Wood Symposium is taking place the Vancouver Convention Centre on Jan. 22. Speaker are discussing the future of wood in a built environment of bigger, taller and more complex buildings. Keep checking back for more blogs and stories from the event or follow us and join the conversation on Twitter here.