Timber Construction: Decay Management

Based on the documents provided, understanding decay prevention is essential before working with Cross-Laminated Timber (CLT) and other timber products. Here's what you need to know:

Key Decay Prevention Principles for Timber and CLT

1. Moisture Management is Critical

Moisture is the primary driver of decay in timber structures. You need to understand:

• Critical moisture thresholds: Timber is generally safe when moisture content stays below 16% for heated interiors (Service Class 1) or 20% for unventilated spaces (Service Class 2)

• End grain vulnerability: End grains absorb approximately 5 times more water than side grain surfaces and require special protection

• Service classifications: Different exposure conditions require different moisture protection strategies:

  • Indoor protected (UC1/UC2)

  • Protected exterior (UC3A)

  • Exposed exterior (UC3B)

  • Ground contact (UC4)

2. Design Elements for Decay Prevention

When designing in Dietrich's software, implement these decay prevention strategies:

• Slope all horizontal surfaces: Model slopes of at least 1:10 (10%) on all exposed timber surfaces to ensure proper drainage

• Eliminate capillary paths: Avoid vertical bolt holes that can wick moisture; use horizontal fasteners where possible

• Protect end grain: Specify appropriate end-grain treatments (silane sealers or epoxy coatings)

• Design inspection access: Include accessible panels for concealed connections so potential decay areas can be monitored

3. Connection Details Matter

Connections are particularly vulnerable to decay:

• Avoid moisture traps: Design connections that won't collect water

• Self-draining joints: Ensure drainage paths that won't be easily blocked by debris

• Capillary breaks: Implement proper flashing, gaskets, or air gaps to prevent water migration

4. Material Selection and Treatment

• Service class-appropriate materials: Use the Material Database in Dietrich's to select materials suited to the exposure classification

• Preservative treatments: For exposed conditions (UC3B+), specify appropriate preservative treatments

• Coating specifications: Document required protective coatings in your models

5. Maintenance Planning

During the design phase, plan for the long-term maintenance of the structure:

• Access for inspection: Design removable trim or access panels for concealed connections

• Cleaning requirements: "Self-draining" joints can fail if debris blocks drainage paths

• Documentation: Use Dietrich's labeling system to clearly identify areas requiring inspection

By addressing these decay prevention principles from the start of your timber project, you'll ensure much greater long-term durability and performance of your CLT and timber structures.