The Mjøstårnet Building 4 Years on, a Symbol of a Green Shift in the Construction Industry?
Mjøstårnet - The Tower of the Lake
When the Mjøstårnet project was completed in March 2019 it was the tallest timber building in the world, holding onto this record for three years being surpassed by the ascent tower in Milwaukee.
The vision of the project was for the mass timber skyscraper to become a symbol of a green shift within construction and proof that tall buildings can be built using local resources, local suppliers and sustainable wooden materials.
Øystein Elgsaas partner from the architectural practice Voll Arkitekter responsible for the design of the building told Dezeen “Wood construction has gained a new renaissance and we are proud to be able to help wooden architecture reach new heights,”
Now four years on we are taking a look at the building and its impact on the construction industry.
Mjøstårnet is located in Brumunddal, Norway an area known for its forestry and wood processing industry, perfectly located for a timber building intending to champion the use of local resources and suppliers.
The structure towers over Norway’s largest lake which endows its name to the project, Mjøstårnet translating to the “The tower of Lake Mjøsa”. The imposing 18-storey tower contains 2,600m³ of timber structures – equating to 11, 000 trees – as well as apartments, offices, a restaurant, roof terrace and hotel.
A construction feat as impressive as this could not have been possible without the introduction of mass timber.
An Introduction to Mass Timber
Provided that the sourced timber is managed sustainably, a shift in the construction industry to wooden structures offers significant carbon reducing potential.
Although engineered wood has existed since the early twentieth century in the form of plywood, a significant innovation was required to create a skyscraper from the material.
This innovation came in the form of Cross Laminated Timber (CLT) developed in Austria in the early 1990s. The material was championed by Gerhard Shickhofer and his PhD thesis on the material’s potential was instrumental in the development of CLT.
Mass Timber refers to engineered wood that can be used as structural building materials. Since its inception this material has grown rapidly in popularity as an alternative to carbon intensive concrete and steel.
Timber Skyscrapers could not have been created without the innovation of mass timber. However, such structures have in turn helped showcase the possibilities of the building material.
The appeal of mass timber is gaining momentum and in 2015 CLT was adopted into the International Building Code (IBC) and in 2021 a new set of changes has permitted structures up to 18 storeys to be created using mass timber.
The Many Types of Mass Timber
Mass timber exists in many forms, and the Mjøstårnet tower was constructed using a combination of CLT and Glue Laminated Timber (Glulam). Glulam was used to create large scale trusses across the façade as well as the internal columns and beams. Whereas CLT was used in walls for secondary load bearing of the three elevators and two staircases.
There are several types of mass timber.
- Glulam is composed of wood laminations bonded together with durable, moisture-resistant adhesives. The grain of all laminations runs parallel with the length of the wood member.
- CLT is the most commonly used type of mass timber. Consisting of layers of kiln-dried dimension lumber oriented at right angles to one another and then glued to form structural panels.
- Dowel-laminated timber, also known as DowelLam or DLT, is a type of mass timber made entirely from wood. DLT panels are constructed from layers of softwood that are connected by friction-fit hardwood dowels.
- Nailed-laminated timber also known as NLT or nail-lam, is manufactured from planks of timber that are placed on their side and nailed or screwed to each other to form panels.
The Environmental challenge of the Construction Industry
The construction industry will play a significant role in our response to global warming. It is estimated that by 2060 we are going to undertake 230 billion square metres of new construction.
According to LETI the conventional residential construction has an embodied carbon of around 800 kilograms of carbon dioxide-equivalent per square metre. If we were to construct all 230 billion square metres to this standard the total emissions from construction alone would surmount to 184 billion tonnes of CO2.
However, the adoption of mass timber could contribute to a significant reduction in the total emissions from the built environment, and projects such as Mjøstårnet are showing us how.
According to environmental advisor and architect Bård S. Solem “Using timber in the load-bearing structures can reduce emissions from material production by up to 85 percent.”
These significant carbon savings can now be seen in buildings across Europe and North America. For the construction of Mjøstårnet around eighteen thousand trees were used to produce the wood products and the adjoining pool. In aggregate, those trees sequester more than two thousand tons of carbon dioxide.
Fire Safety and Precautions
Martin Lunke, a project manager for Hent, the contractor responsible for the Mjøstårnet told The New Yorker that locals were initially referring to the building as “the world’s biggest torch.”
However, the Fire Strategy for the building was extensive. The report states the main load bearing system must be designed to withstand 120 minutes of fire whilst the secondary load bearing floors must withstand 90 minutes of fire.
Also included in the fire design for the building were burnout tests performed in 2016 SP Firetech in Trondheim, Norway. The tests put large glulam columns in furnaces and were burnt for 90 minutes. The furnace was then shut down and the columns continued to char, however after several hours the temperature began to decrease and the burning stopped. The test was designed to show that the structure would self extinguish and prevent a collapse of the building in the case of a fire.
The project featured numerous other fire safety features including an upscale sprinkler system, fire safety systems to control the spread of the fire, a firestop material incorporated into the façade, and fire strips to protect the steel components of the building.
It is important to know the risks of building with mass timber and be able to mitigate them through design and testing. Through fire safe designs on projects such as Mjøstårnet can show that it is safe and possible to build skyscrapers from mass timber.
The Current Outlook on Mass Timber
Although popularity for mass timber construction is on the rise the movement still faces challenges.
The Mjøstårnet development cost a hundred and thirteen million dollars, estimated at eleven per cent more expensive than what it would of cost in concrete and steel (A not insignificant 12.4 million dollars).
The sustainability benefits of mass timber only apply to regions of plentiful forests and harvestable renewable trees. The carbon savings of the materials are reduced by transport to regions without access to the natural resource.
However, the signs of a green shift are there whether it is; the fact it only took three years for the record for the tallest timber building to be topped (and soon to be recrowned), or the materials introduction into international building codes allowing structures of over 18 stories.
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