The Catalyst building in Spokane, Washington, stands as a landmark achievement in mass timber construction and zero-carbon building design. At 159,000 square feet across five stories, this structure demonstrates how engineered wood products can serve as the primary structural material for large-scale commercial buildings while meeting rigorous sustainability targets. For building professionals specifying materials for similar projects, understanding the technical specifications of the cross-laminated timber (CLT) and glulam components used in the Catalyst building offers valuable lessons in material selection, performance verification, and integration with other building systems.
This article examines the material specifications of the mass timber products used in the Catalyst building, their structural and environmental performance characteristics, and the standards that govern their specification for zero-carbon commercial construction. Washington was the first state to adopt tall mass timber building codes, providing the regulatory framework that made projects like Catalyst possible.
CLT and Glulam Material Specifications for the Catalyst Building
The Catalyst building incorporates approximately 141,000 cubic feet of locally sourced mass timber products, serving as both the structural framework and exposed interior finish. The material selection centered on two primary engineered wood products: cross-laminated timber (CLT) for floor and roof panels, and glued laminated timber (glulam) for columns and beams.
Cross-Laminated Timber Panel Specifications
The CLT panels used in the Catalyst building were manufactured to meet ANSI/APA PRG 320 standards, the governing North American standard for cross-laminated timber. Key specifications include:
- Lumber grade: E1-grade (spruce-pine-fir) for major stress-carrying layers with 1950f-1.7E machine stress-rated lumber
- Panel build-up: 5-ply and 7-ply configurations depending on span requirements, with panel thicknesses ranging from 6.875 inches to 9.875 inches
- Adhesive system: Polyurethane-based (PUR) adhesive meeting the durability requirements of ANSI/APA PRG 320 for dry-use service conditions
- Panel dimensions: Custom panel sizes up to 8 feet wide by 40 feet long to accommodate the building’s 30-foot structural bay spacing
- Surface finish: Sanded appearance grade on exposed soffits, with mill-run finish on concealed surfaces
Glulam Column and Beam Specifications
The glulam members provide the primary vertical support and beam framing for the Catalyst building. Specifications included:
- Combination symbol: 24F-1.7E (Douglas fir) for beams, providing a design bending stress of 2,400 psi
- Column grade: Combination 2, providing compressive strength parallel to grain of 1,750 psi
- Appearance grade: Architectural appearance (A-grade) for all exposed columns, with specified grain orientation and color-matched finger joints
- Fire-resistance treatment: No supplemental fire-retardant treatment required; the inherent char rate of mass timber provides the required 1-hour and 2-hour fire-resistance ratings through sacrificial char layer calculations
Material Sourcing and Supply Chain
The mass timber was sourced from forests within a 500-mile radius of the project site, supporting the project’s embodied carbon reduction goals. The local sourcing strategy reduced transportation emissions and supported regional forestry economies. Each timber component was traceable to its source forest through chain-of-custody certification under the Sustainable Forestry Initiative (SFI) program.
Structural Performance and Engineering Design with Mass Timber
The structural engineering for the Catalyst building required careful coordination between the mass timber structural system and the mechanical, electrical, and plumbing systems. The exposed timber structure also served as the finished interior ceiling, eliminating the need for suspended ceiling systems and reducing material usage.
Structural Load Design Parameters
The mass timber structural system was designed to resist the following loads:
| Load Type | Design Value | Applicable Standard |
|---|---|---|
| Dead load | 25 psf (CLT panel + finishes) | IBC 2018 Table 1607.1 |
| Live load (office) | 50 psf (reducible) | IBC 2018 Table 1607.1 |
| Snow load | 30 psf ground snow load | ASCE 7-16 |
| Wind load | 110 mph (ultimate design) | ASCE 7-16 |
| Seismic design category | C | IBC 2018 / ASCE 7-16 |
| Floor vibration | 1.0% critical damping ratio | AITC/TECC TG-1 |
Vibration Control in Mass Timber Floors
One of the critical engineering challenges for CLT floor systems is controlling perceptible vibration. The Catalyst team addressed this through a combination of strategies:
- Increasing CLT panel thickness beyond minimum structural requirements to achieve a fundamental frequency above 8 Hz
- Adding a 2-inch lightweight concrete topping slab bonded to the CLT panels to increase mass and damping
- Designing glulam beam spans to limit deflection under live load to L/480 rather than the code-minimum L/360
- Using finite element modeling to verify vibration performance across all bay configurations before fabrication
Connections and Fasteners
The connection design for the Catalyst building used concealed steel plates and self-tapping screws to maintain the clean exposed timber aesthetic. Connection details included:
- Column-to-beam connections using concealed slotted steel plates with dowel-type fasteners
- CLT panel-to-panel joints using self-tapping screws at 12 inches on center along panel edges
- CLT-to-glulam connections using angle brackets and annular ring shank nails at 6 inches on center
- Lateral force-resisting system using steel cross-braces in stair and elevator cores, with timber-concrete composite diaphragms at each floor level
The NFPA has adopted tall mass timber provisions allowing wood structures up to 18 stories, expanding the market for the types of material systems demonstrated at Catalyst.
Fire Performance and Building Code Compliance for Mass Timber
The Catalyst building’s fire protection strategy relies on the inherent charring behavior of mass timber rather than applied fire-retardant coatings. This approach reduces ongoing maintenance costs and environmental impacts associated with chemical treatments.
Char Rate and Sacrificial Layer Design
The fire-resistance rating for mass timber elements is calculated based on the char rate of wood, which is well-documented through extensive testing:
- Char rate: 1.5 inches per hour for CLT panels under standard fire exposure (ASTM E119)
- Sacrificial layer: The outermost ply of each CLT panel is designated as a sacrificial char layer, with the remaining plies providing the structural capacity during a fire event
- 1-hour rating: Requires 3.5 inches of effective remaining cross-section after char calculation, achieved with 7-ply CLT panels
- 2-hour rating: Requires 4.75 inches of effective remaining cross-section, achieved with additional CLT thickness or protected membrane
Sprinkler Systems and Active Fire Protection
In addition to passive fire resistance through the mass timber char layer, the Catalyst building includes:
- Automatic sprinkler system throughout all occupied areas (NFPA 13 compliant)
- Fire alarm system with voice evacuation for the five-story building
- Smoke control system designed to maintain tenable conditions in egress paths
- Standpipe system in the stairwells for fire department use
The combination of char-layer passive protection and active sprinkler systems allows the exposed timber interior while meeting all IBC fire-resistance requirements. This approach has been validated through full-scale fire tests on similar mass timber assemblies.
Embodied Carbon and Lifecycle Performance of Mass Timber Materials
The material science behind mass timber’s carbon performance is central to the Catalyst building’s achievement as one of the first buildings certified zero-carbon by the International Living Future Institute.
Carbon Accounting for Mass Timber
The embodied carbon benefits of the Catalyst building’s mass timber structure can be quantified through several metrics:
| Metric | Catalyst Building Performance | Comparison to Steel/Concrete Equivalent |
|---|---|---|
| Biogenic carbon stored | 5,000 metric tons CO2e | N/A (steel/concrete store no biogenic carbon) |
| A1-A3 (cradle-to-gate) emissions | 89 kg CO2e/m3 | 75% reduction vs. reinforced concrete |
| Thermal bridging reduction | Continuous insulation with minimal thermal bridging at connections | Superior to steel frame with curtain wall |
| Operational energy offset | Onsite PV array meets 100% of annual energy demand | Passive House-level envelope performance enabled by mass timber |
| End-of-life recyclability | 100% biodegradable or reusable | Steel: 98% recyclable; Concrete: difficult to separate |
Moisture Management and Durability
Mass timber buildings require careful moisture management during construction and throughout the service life. The Catalyst team implemented the following measures:
- Moisture content verification at time of delivery (target: 12% +/- 2% moisture content)
- Temporary weather protection during erection phase, including membrane wrapping of CLT panels stored on-site
- Integrated vapor-permeable water-resistive barrier (WRB) in the exterior wall assembly to allow outward drying
- Continuous monitoring of in-service moisture content using embedded sensors in representative CLT panels
- Design of all moisture-vulnerable connections with corrosion-resistant fasteners (hot-dip galvanized or stainless steel where exposed to potential condensation)
Acoustic Performance of Mass Timber Assemblies
For a multi-story commercial building, acoustic separation between floors is a critical performance requirement. The Catalyst building achieved the following acoustic ratings for typical floor assemblies:
- STC 55: CLT panel + 2-inch concrete topping slab + acoustic underlayment + finished floor (meets IBC requirement for STC 50 minimum between adjacent tenant spaces)
- IIC 52: Same assembly tested for impact isolation (meets IBC requirement for IIC 50 minimum)
- Supplemental acoustic treatment: Acoustic clouds suspended from the CLT ceiling in open office areas to reduce reverberation time to 0.6 seconds
The LEED Zero certification framework provides standards for net-zero carbon building design that projects like Catalyst are helping to validate.
The Catalyst building in Spokane offers building material specifiers a real-world example of how mass timber products can meet the structural, fire, acoustic, and environmental performance requirements of large-scale commercial construction. The material specifications developed for this project, combined with the rigorous testing and verification protocols employed, provide a template for specifying CLT and glulam in zero-carbon buildings nationwide. As more states adopt tall mass timber provisions and zero-carbon certification standards become more widespread, the construction methodologies validated at Catalyst will continue to influence sustainable building material specifications for years to come. Timber office buildings using mass timber structural systems and facade strategies are increasingly demonstrating the viability of this approach for sustainable workplaces across North America.