Mass Timber Moisture Content: Optimal Levels for Material Performance

Mass timber is designed to provide strength and stability, but its moisture content plays an important role in how the material performs. Wood that is too dry can shrink and crack, while excessive moisture can increase the risk of mold and decay.

Understanding the moisture risk scale helps construction teams recognize potential issues and determine when conditions may need to be corrected.

Understanding the Moisture Content

Wood moisture content (MC) is the amount of moisture present in the wood. The scale below illustrates how risk changes as moisture levels increase or decrease.

• Below 6% MC | Too dry: Wood may absorb moisture and expand, potentially causing cracking, checking, or stress on structural connections.
• 6%–16% MC | Lower risk: Generally a safer range, although the ideal moisture content depends on the building's intended in-service conditions.
• 16%–20% MC | Elevated risk: Higher moisture levels
  warrant closer monitoring and investigation into potential moisture sources.
• 20%–28% MC | Critical risk: Prolonged exposure can increase the risk of mold and decay. Corrective action may be needed.
• Above 28% MC | Severe risk: Wood is increasingly susceptible to fungal decay, particularly when elevated moisture persists.

These ranges are general guidelines. Actual risk depends on exposure duration, environmental conditions, and the wood's intended use.

Monitoring and Managing Moisture

Mass timber can absorb moisture during transportation, on-site storage, and construction. Even when materials are covered, rainwater can enter through openings or accumulate on the wood. During construction, moisture-latent materials can slow acclimation or pipe leaks or water intrusion can expose mass timber.

Monitoring moisture content helps teams identify changing conditions and determine when intervention is needed. The appropriate response depends on the readings:

• Monitor: Track moisture levels over time to identify potential issues.
• Manage: Use climate control to maintain appropriate conditions.
• Mitigate: Apply humidification or dehumidification when moisture levels need correction. Connected systems can do this automatically and assist in seamless and gradual material acclimation.

Identifying moisture issues early gives construction teams an opportunity to address them before the wood is enclosed or prolonged exposure leads to further concerns.

Polygon provides moisture monitoring and climate-control solutions to help construction teams manage moisture levels and maintain appropriate conditions throughout mass timber projects.

Visit Mass Timber Moisture Management to learn more.