What Is Cross-Laminated Timber (CLT) Floor Design?

Structural behavior

CLT panels (3, 5, 7+ layers — the cross-lamination giving the two-way action) span 10-20 feet typically (longer with the deeper panels or the composite concrete topping). The design checks: bending (the effective section — only the longitudinal layers count fully), rolling shear (the cross-layers' shear perpendicular to grain — the CLT-specific check that often governs), and deflection (the serviceability — the span/depth ratios tighter than concrete). PRG 320 (the product standard) and the NDS (with the CLT provisions) govern.

Vibration and acoustics

Floor vibration (the light floor's dynamics — the fundamental frequency and the damping; the design targets the perceptibility thresholds — the concrete topping or the increased panel depth solving the lively floors), and acoustics (the impact and airborne sound — the layered assemblies: the CLT plus the acoustic mat plus the topping achieving the IIC/STC ratings). The acoustic detailing (the flanking paths — the panel joints and the wall connections) matters as much as the assembly.

Fire, connections, and construction

Fire (the charring calculation — the sacrificial layer for the required duration; the panel joints' fire performance), connections (the panel-to-panel splines, the panel-to-support brackets — the proprietary connectors with the tested capacities; the diaphragm action — the floor as the lateral system's diaphragm), and construction (the just-in-time prefabrication — the panels craned directly from the truck; the moisture protection — the weather-tightness plan during erection). The MEP integration (the penetrations planned — cutting CLT on site is the expensive surprise).

The bottom line

CLT floors span 10-20 ft per PRG 320/NDS — check rolling shear, vibration, and acoustics; detail the charring fire design and the diaphragm connections; protect from moisture during erection.

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