"Tall timber" — building tall structures predominantly in engineered wood — is today one of the most closely watched fronts in structural engineering, with a height record that changes hands almost every year. But the real technical story is not the race for metres: it is the specific problems each project has had to solve to go beyond the limit of the one before it.
From Brock Commons to the Mjøsa Tower
The Brock Commons Tallwood House at the University of British Columbia in Vancouver (2017, 18 storeys, 53 metres) was the first to demonstrate at this scale that a mixed structure — GLULAM columns, CLT floor slabs, just two reinforced-concrete cores for lateral stiffness — could compete on construction time with an equivalent concrete building, cutting it by roughly half. Two years later, the Mjøsa Tower in Brumunddal (Norway, 2019, 18 storeys, 85.4 metres) pushed the record higher with a conceptually different approach: almost entirely in GLULAM even for the lateral bracing elements, without relying on a concrete core as the main stiffness element — a choice made possible by a site with relatively modest wind and seismic loads compared with other locations.
The problems that matter more than height itself
The real engineering bottleneck of tall timber is not "how high can wood go" in the abstract, but a series of specific technical problems that worsen with height. Differential shrinkage is the first: every CLT layer or GLULAM element, however industrially dried, keeps losing residual moisture in its first years in service, shrinking slightly along the direction perpendicular to the grain — a negligible effect on a three-storey building, but on a twenty-storey building, summed floor by floor, it can generate significant cumulative vertical misalignments between timber elements and the concrete cores, which do not shrink the same way. The second problem is lateral stiffness: wood, while excellent in compression and tension along the grain, has a lower elastic modulus than steel and concrete, so resisting horizontal wind and seismic forces almost always requires integrating rigid concrete cores or steel bracing — "pure" tall timber, with no hybrid element, remains today the exception rather than the rule even in the most ambitious projects.
Plyscrapers: the pursuit of 40-80 storeys
Beyond the records already achieved, academic research and some industrial feasibility studies look to "plyscrapers" — timber skyscrapers of 40 to 80 storeys — as the next technical horizon. These studies, carried out among others by research groups in Canada, the UK and Japan, do not propose all-timber structures at those heights: they model hybrid systems where wood handles vertical loads and part of the mass, while concrete cores or steel mega-braces absorb horizontal forces — the same hybrid logic already seen in built skyscrapers, simply pushed to a much larger scale. The challenge that remains open is not so much structural as regulatory and insurance-related: fire codes for very tall buildings (above 50-60 storeys) were historically written with incombustible structures in mind, and revising them to systematically include wood as a primary structural material requires a technical and regulatory validation process that moves more slowly than the sheer engineering capacity to build those buildings.
The hybrid compromise as a standard, not a fallback
It's worth correcting a simplified narrative that sometimes accompanies these projects: the hybrid timber-concrete structure is not a lesser compromise compared with a hypothetical purer "all-timber skyscraper", but the most engineeringly sensible solution for most of the sites and heights involved. Each material is used where its mechanical properties are genuinely advantageous: wood for lightness and assembly speed under vertical loads, concrete or steel where concentrated stiffness against horizontal forces is needed. The real innovation of contemporary tall timber is not "replacing" the other structural materials, but integrating them in optimized proportions different from the traditional ones.