What Is Cross-Laminated Timber Floor Vibration?
CLT floor vibration is the footfall-induced bounce and perceptibility in mass-timber floors — the serviceability criterion that often governs CLT floor design. CLT panels are lighter than concrete, so footstep impacts create more noticeable vibration; the design must satisfy acceleration and frequency limits for human comfort. Getting the vibration right separates successful mass-timber buildings from bouncy ones.
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Why vibration governs
Strength rarely controls CLT floor design — a panel strong enough for the loads is often too lively for comfort. Human perception thresholds (peak accelerations under footfall, natural frequency above ~8-9 Hz for residential) drive the panel thickness and span. Long-span CLT floors without attention to vibration feel bouncy and cheap — the number-one occupant complaint in under-designed mass timber.
Design methods
The engineer checks: fundamental frequency (stiffness and mass — thicker panels, shorter spans, or added screed mass raise it), footfall response (the AISC Design Guide 11 / SCI P354 methods adapted for timber, or the CLT-specific provisions in the timber design standards), and damping (CLT's inherent damping is low — 1-2% — so the design relies on frequency separation rather than damping). Concrete screeds or toppings add mass and damping where needed.
Construction details
Panel-to-panel connections affect the effective stiffness (screwed splines vs. half-laps — the connection detail enters the vibration model), supports must be as modeled (a panel designed as continuous that gets built as simple-span vibrates differently), and the floor build-up (toppings, ceilings) changes mass and damping. Verify the as-built matches the vibration assumptions — this is a serviceability design where field deviations are felt literally.
The bottom line
CLT floor vibration (footfall comfort) often governs panel design — check frequency and acceleration per DG11/P354 methods. Thicker panels, shorter spans, or added mass where needed.
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