Meteoric Rise of Cross-Laminated Timber Construction: 50 Projects that Use Engineered-Wood Architecture

Timber is a natural, renewable material, easy to fabricate, and with low-carbon emissions. As a construction material, however, when put under enough directional force along its grain, sawn timber is structurally unstable, so deemed unsuitable under higher loads. In comparison, the manufacture of cross-laminated timber (CLT) involves simply gluing multiple layers of timber together at right angles. By crossing the direction of the grains, CLT achieves a far higher level of structural rigidity along both axes. CLT boards start with a minimum of three layers but can be strengthened further with the addition of more. Simply put, due to the complex physics involved in the perpendicular lamination, the strength of CLT board is similar to that of reinforced concrete, and has proven performance under seismic forces.

So what’s new? Wood’s been around for long enough now, and we’ve been using it as a building material for centuries. Surely this isn’t the first time someone’s realized it gets stronger the more you use it? Well… as you’d expect, the changing popularity of cross-laminated timber in construction does coincide with a greater understanding and focus on environmental causes, but the relationship hasn’t always been positive.

50-20 years ago, the environmental crisis was based on deforestation, not carbon footprints, meaning wood and wood products in all their forms were demonized, with campaigners arguing that wood belonged in the ground where it could continue to do good, rather than cut down and used to make buildings. The preferred alternative materials, however, were carbon-intensive steel and concrete. In the early 21st century, as a more sustainable and responsible reforestation-focused wood industry grew, CLT started to become the material du jour for sustainable and, indeed, circular building projects, with organizations like Circular CLT dedicated to reducing CLT production waste and finding solutions for it such as biomass-fuelled hydrogen power. But how did CLT use in construction begin? And what does it mean for the future?

The pioneers of cross-laminated timber (CLT) construction

In September 2016, Alison Brooks Architects, in collaboration with the American Hardwood Export Council (AHEC), Arup, and the London Design Festival, built The Smile at the Chelsea College of Art, London, UK, ‘showcasing the structural and spatial potential of cross-laminated American tulipwood,’ explains the architects, as the project uses CLT’s structural capacity to cantilever visitors in its 34m-long curve, up to three meters above the ground, without additional support.

Courtesy of LEVER Architecture

The year before the CLT-build Smile was revealed, however, architects Hawkins/Brown had already begun to present the structural capacity of CLT with The Cube, a ten-story apartment block down the road in Hackney, London. In the building, ‘CLT panels are set into a steel frame, bracing it to form an integral part of the structure,’ explains Hawkins/Brown. Around the same time, meanwhile, the primary goal of Albina Yard in Portland, USA, by LEVER Architecture, the first US building to utilize CLT, was to promote the use of the domestic wood product by combining a glue-laminated timber frame with CLT panels. And more recently, the Mass is More Installation from IAAC + Bauhaus Earth references Mies van der Rohe’s German Pavilion at the 1929 Barcelona Exposition, by reflecting the formal grid of the original pavilion, using CLT.

Simplicity and circularity of CLT

After extensive field experience, the fabled three little pigs found that straw and wood are two of the least structurally sound materials with which to build. Thankfully, however, architecture office Kollektiiv didn’t include old nursery rhymes in their material research for the Straw Chapel in Tallinn, Estonia, which holds up a wall and ceiling of straw bales with CLT arches. With all its components prefabricated, the pavilion was built both for, and by, the local community.

The possibilities of prefabrication, meanwhile, make even complex architectural solutions more achievable, like CRAB Studio’s design of an Innovation Center at the Arts University Bournemouth, UK, which uses CLT to form irregular sections of wall, floor, and roof, and playfully combines the material’s colorful or natural wood finish with voids of light. Alternatively, the Voxel Quarantine Cabin in Barcelona, Spain, took waste material created during the CLT-production process, and turned it ‘into a facade that showcases the organic complexity of the tree,’ as the architects, Valledaura Labs, explains.

Courtesy of CRAB Studio

Courtesy of IKD

The rise of the plyscraper

Along with its structural integrity, there are many other assumed challenges for buildings made from wood to overcome, namely its inherent flammability and warping under humidity. Studies have shown, however, that although cross-laminated timber is highly flammable, it also has a Resistance to Fire rating of REI 90 (meaning it retains the sufficient load-bearing capacity for up to 90 minutes), compared to unprotected steel’s REI 15 rating. Hakwins/Brown’s decision to reconstruct the Freemen’s School Swimming Pool with structural CLT, after the original building was destroyed in a fire, exemplifies this, and also proves the material performs when dealing with the challenges of a pool environment, too.

It’s thanks to this structural load-bearing capacity, even under extreme conditions such as humidity and fire, that means in 2021 the International Code Council ruled that CLT buildings could come under the International Building Code IV-A, meaning the maximum height of a CLT ‘plyscraper’ could reach up to 270 feet. At over 260 feet tall, the Sara Kulturhus Center in Sweden is currently one of the world’s tallest high-rise timber structures, with a ‘load-bearing structure built entirely without concrete, speeding up construction time and drastically reducing the carbon footprint,’ explains the architects White Arkitekter.

With CLT research, innovation, regulations, trust, and, indeed, timber-frame buildings themselves growing all the time, the only way to go is up.

Cross-Laminated-Timber Cottage / Kariouk Associates

WoodTek HQ / Origin

Puukuokka Housing Block / OOPEAA

The Cube / HawkinsBrown

The Smile / Alison Brooks Architects

The CLT House / KAWA DESIGN GROUP ARCHITECTURE

Courtesy of KAWA DESIGN GROUP Architecture

CLT Multi Confort Office Building / Tecto

Albina Yard / LEVER Architecture

Moholt Timber Towers / MDH Arkitekter

Freemen’s School Swimming Pool / HawkinsBrown

Santo CLT Office / Junichi Kato & Associates

“KITERASU” Model CLT Building at Kuse Station / ofa

University of Massachusetts Amherst Design Building / Leers Weinzapfel Associates

Indiana Hardwood CLT / IKD

Courtesy of IKD

The Seed House / fitzpatrick+partners

Courtesy of fitzpatrick+partners

Timber School in Kuhmo / ALT Architects

Flatiron Office Building / Works Partnership Architecture

Arimunani School / Aulets Arquitectes + Aixopluc

Villa Wood / NORD Architects

95PLA Refurbishment / Vallribera Arquitectes

CLT House / FMD Architects

Nordtvet Farm Kindergarten / MORFEUS arkitekter

Community Center / NORD Architects

The Voxel Quarantine Cabin / Valldaura Labs

Smartware CLT Office Building / Vertical Studio

55 Southbank Boulevard / Bates Smart

Innovation Center for the Arts University Bournemouth / CRAB Studio

Courtesy of CRAB Studio

The Float / Studio RAP

Speehuis House / Spee Architecten

Lipno Lakeside Cabin / Les Archinautes

1721 House / HARQUITECTES

m.o.r.e. Cabin / Kariouk Architects

NIOA Timber Tower / KIRK Studio

Wintringham Primary Academy / dRMM

Vélizy Morane Saulnier Apartments / DREAM

Sara Kulturhus Center / White Arkitekter

B&O Wooden Car Park / HK Architekten, Hermann Kaufmann + Partner ZT

CLT House / Unknown Works

Biv Punakaiki Cabin / Fabric

Straw Chapel / Kollektiiv

Bocaina-Paraty House / Cicero Ferraz + Fábio Mosaner

Octothorpe House / Mork-Ulnes Architects

Mass is More Installation / IAAC + Bauhaus Earth

Ziggurat and Rhomboid Buildings London Design District / Mole Architects

Fuggerei NEXT500 Pavilion / MVRDV

St. Olavsvei 18 Residential Building / Oslotre

Houston Endowment Headquarters / Kevin Daly Architects + PRODUCTORA

6 Housing Units in Paris / mobile architectural office

High Street Apartments / Gardiner Architects

HAUT Amsterdam Residential Building / Team V Architecture

Find more projects that use Cross-Laminated Timber in this My ArchDaily folder created by the author.

This article is part of the ArchDaily Topics: Circular Economy. Every month we explore a topic in-depth through articles, interviews, news, and architecture projects. We invite you to learn more about our ArchDaily Topics. And, as always, at ArchDaily we welcome the contributions of our readers; if you want to submit an article or project, contact us.

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