A tall timber building is a multi-story structure in which engineered timber products serve as primary load-bearing elements. Cross-laminated timber (CLT), laminated veneer lumber (LVL), and glued laminated timber (glulam) are the dominant load-bearing materials, frequently combined with concrete or steel components in hybrid construction systems. This approach enables timber structures to reach heights of 10 stories and beyond while maintaining timber as the structural core.
Engineered Timber Products
Cross-laminated timber (CLT) is the most prevalent material in tall timber construction. CLT panels consist of solid-sawn lumber or engineered lumber boards laminated perpendicular to one another, achieving panels typically 60–500 mm thick and up to 4.8 m × 19.2 m in size. Characteristic strength values for CLT include bending strength of 12–16 MPa (parallel to grain) and modulus of elasticity between 7,000–11,000 MPa. Glued laminated timber beams offer bending strength of 22–39 MPa depending on grade and lamination configuration. LVL products achieve modulus of elasticity values of 11,000–14,000 MPa and are used primarily for secondary load-bearing and stabilizing elements.
Structural Performance and Fire Safety
Tall timber buildings typically employ hybrid systems combining timber with reinforced concrete cores or steel bracing to manage lateral loads from wind and seismic forces. The concrete core or steel framework resists horizontal forces while timber elements carry vertical loads. Charring rate of timber under fire is approximately 0.6–0.7 mm/min, allowing structural integrity to be maintained through oversizing of cross-sections or encapsulation methods. Fire-rated timber assemblies commonly achieve 30–90 minute fire resistance ratings through gypsum board protection, intumescent coatings, or combination systems.
Sustainability and Building Regulations
Timber sequestration in structural elements typically ranges from 300–800 kg CO₂ eq/m³ of floor area, providing carbon storage benefits over the building lifecycle. Embodied carbon of CLT averages 100–250 kg CO₂/m³, significantly lower than concrete (300–350 kg CO₂/m³) or steel (1,500–2,500 kg CO₂/m³). Building regulations in Europe (EN 1995-1-1 Eurocode 5), North America (NDS, IBC), and Australia (AS 1720.1) permit timber structures to reach increasing heights, with CLT systems commonly approved for 10–15 story residential and commercial buildings. Water absorption of CLT in outdoor conditions reaches 15–20% by weight; protective barriers and coatings limit moisture uptake to 12–15% during construction.
Design Considerations
Moisture management is critical; target equilibrium moisture content in interior timber is 8–12%. Wood species selection affects dimensional stability: European spruce has modulus of elasticity of 10,000–12,000 MPa, while North American Douglas fir ranges 11,000–13,000 MPa. Connection systems typically employ steel dowels, bolts, or screws with load capacities of 2–8 kN per fastener depending on configuration. Panel-to-panel connections in CLT assemblies are designed for both vertical loads and horizontal shear, with typical joint slip under service load limited to 5–10 mm.