Wooden skyscrapers could be the future for cities

Demographic and Environmental Context

• Global population is projected to reach nearly 10 billion by 2050, with two-thirds residing in urban areas, creating severe space constraints.
• Current high-rise construction relies on concrete and steel, which carry a substantial carbon footprint.

Proposed Structural Shift

• Architectural advocates propose transitioning from concrete and steel to timber, likening the former to fossil fuels (petrol/diesel).
• A study indicates that constructing a 125-meter skyscraper from wood could reduce its carbon footprint by up to 75%.
• Wood offers logistical advantages over concrete: it is lighter, sustainably grown, and absorbs carbon dioxide during tree growth.

Technological Solution: Cross-Laminated Timber (CLT)

• Regular timber lacks the malleability and strength for high-rises; engineers developed CLT to address this.
• CLT involves gluing wood layers at 90-degree angles to create a stable, lightweight material comparable in strength to concrete and steel.
• Fire Safety Mechanism:
  • Wood chars when burned, creating an insulating layer that protects the structural core.
  • Unlike steel, which softens and may collapse under high heat, charred timber often extinguishes itself once the flame source is removed.
  • Historical precedent: Steel roofs have collapsed in fires where wooden roofs remained intact.

Current Construction Status and Examples

• London architecture firm Witherington is designing CLT buildings and reports construction speeds of approximately one floor per week (twice as fast as concrete).
• Witherington recently completed Britain's first high-rise wooden apartment block and the world's largest timber-based building.
• The completed London structure features a core made from over 2,000 trees sourced from sustainable forests.
• CLT high-rises are currently being constructed in Scandinavia, Central Europe, and North America.
• Height Limit: No CLT building currently exceeds 55 meters in height.

Future Projections and Challenges

• The University of Cambridge's research center, in collaboration with a London practice, has conceptualized the "Oakwood Tower," a 300-meter timber skyscraper atop the Barbican.
• Design Specifics: The proposed Oakwood Tower would feature base columns measuring 2.5 meters square, composed of small, glued timber elements.
• Growth Trajectory: Experts anticipate incremental height increases from the current 50-meter baseline, expecting a significant "step change" to approximately 100 meters in the near future.
• Economic and Social Hurdles:
  • Costs for wooden skyscrapers remain largely unknown but could be reduced through factory prefabrication of large sections.
  • Public perception requires adjustment; city dwellers must be convinced that CLT does not burn like ordinary wood.
• Current adoption is highest in low-rise structures; future expansion depends on planner approval and overcoming cost/perception barriers.