The World’s Tallest Timber Building

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In the quiet town of Brumunddal, Norway, set against the serene backdrop of Lake Mjøsa, stands a structural marvel that is forcing the global construction industry to unlearn everything it thought it knew about timber. Mjøstårnet, an 18-storey mixed-use tower reaching a height of 85.4 meters, is not just a building; it is a proof of concept. 

Ratified by the Council on Tall Buildings and Urban Habitat (CTBUH) as the world’s tallest all-timber building upon its completion in 2019, it stands as a sophisticated rebuttal to the idea that wood is a “primitive” material relegated to cabins and low-rises.

By trading carbon-heavy steel and concrete for advanced mass timber, investor Arthur Buchardt and the engineering minds at Moelven Limtre have created a skyscraper that breathes. 

Here are six surprising secrets behind the design and high-tech assembly of this timber titan.

The Hyper-Local 15km Radius 

Mjøstårnet is the ultimate example of “locavore” architecture. While global supply chains often see materials shipped across continents, the vast majority of this tower was sourced from the building’s own backyard. Approximately 16,000 spruce trees were harvested to produce the 4,000 cubic meters of timber required for the project.

The raw planks were sourced from sawmills across southeast Norway, with the trees harvested from sustainable forests in the Ringsaker area. These materials were then processed into glulam (glued-laminated timber) structures and façade elements at Moelven Limtre’s facility, located a mere 15 kilometres from the construction site. 

This hyper-local approach didn’t just minimise transport emissions; it also leveraged generations of local Norwegian wood-processing expertise.

The Fire-Resistance Paradox

The most common question regarding a timber skyscraper is: “What happens in a fire?” The answer is a surprising engineering paradox. Mjøstårnet is designed to be “self-extinguishing.” Rather than relying on traditional fireproofing, the design utilises a “charring” strategy. 

In a fire, the outer layer of the thick glulam beams chars at a predictable rate, creating an insulating layer that protects the inner core from heat and preserves its structural integrity.

Technical fire safety specifications include:

• 120-Minute Load-Bearing System: The main structure is designed to withstand a two-hour fire—enough for a full burnout without collapse.
• 0.7 mm/min Charring Rate: Standardised calculations ensure that even after 120 minutes (84mm of char), the core remains strong.
• Invisible Thermal Protection: Steel connections are “slotted-in” and embedded 85mm deep into the timber. This ensures that the wood, which chars to 84mm over two hours, insulates the steel, keeping it below critical temperatures.
• Intumescent Sealing: Gaps are fitted with strips that expand 20 times their size at 150°C, sealing off internal steel from fire exposure.

The “Concrete Hack” for Sea-Sickness

Timber is significantly lighter than concrete, but in the world of skyscrapers, lightness can be a liability. Tall timber buildings are susceptible to “horizontal acceleration”, the wind-induced swaying that causes resident nausea or “sea-sickness.” To solve this, Voll Arkitekter and the engineers at Sweco employed a clever “concrete hack.”

While floors 2 through 11 use the “Trä8” wooden cassette system (a high-performance composite of glulam joists and LVL-C panels with an 8m span), the top seven floors (levels 12 to 18) utilise 300mm thick concrete slabs. 

This added mass at the top of the tower slows down the building’s movement, ensuring comfort without the need for expensive “Tuned Mass Dampers” (TMDs). Interestingly, the engineers borrowed structural damping data from the “Treet” building in Bergen to calibrate these movements.

Zero-Tolerance “Lego” Assembly

Constructing Mjøstårnet was less like a traditional job site and more like a high-tech assembly line. All structural elements were processed using Computer Numerical Control (CNC) machines, ensuring extreme geometrical precision with practically zero tolerances.

The assembly was remarkably efficient: steel plates were installed into the glulam columns at the factory before transport, and the entire structure was erected in six stages without any external scaffolding. 

Precision was most critical at the base connections; if the foundation’s steel plates were even slightly misaligned, the pre-drilled timber elements further up the tower would have been impossible to mount.

Mjøstårnet Assembly Timeline

The Aerodynamic Pergola

The architectural “crown” that gives Mjøstårnet its final height is the rooftop pergola. While the rest of the building’s primary structure is Spruce, the pergola is crafted from Cu-impregnated Pine for enhanced durability against the elements.

To prevent the shrinkage cracks common in large solid wood sections, these beams were designed as hollow sections composed of four 90mm-wide beams glued together. Furthermore, every corner of the pergola was rounded with a 140mm radius. This rounding is not merely aesthetic; it improves the building’s aerodynamics, reducing the wind resistance that contributes to the tower’s sway.

A Living, Breathing Mixed-Use Ecosystem

Mjøstårnet is a dense, multi-functional community. It houses the “Wood Hotel” (72 rooms), 33 residential apartments, office space, a restaurant, a rooftop terrace, and conference rooms. There is even a public swimming pool located next door on the ground level.

The complexity of the tower is represented by a sophisticated hybrid of materials, where each component is optimised for performance:

• Wood (Glulam, CLT, solid wood): 34%
• Insulation: 33%
• Concrete: 26%
• Steel: 1%
• Other materials: 6%

TERRAVERTA: The Blueprint for the Future

While newer structures like Ascent in Wisconsin have since claimed the title of world’s tallest timber building, Mjøstårnet remains the definitive “blueprint” for the future. It proved that the high-rise timber industry could surpass early pioneers like Brock Commons by using local resources and smarter mass distribution.

The architects claim that the structural principles established in Brumunddal are so robust that it is now technically possible to double the height of timber buildings using these same methods. As we enter the “Timber Revolution,” Mjøstårnet stands as the undeniable proof that our urban future can be built from the forests we grow.

Create a future built for growth. Enquire about a TERRAVERTA habitat of your own.