information/FAQs

Designing for Durability - Introduction

Durability can be defined as the capacity of a timber product, component, system, building or structure to perform its function for a specified period of time.

This definition does not negate a designer's responsibility to consider the level of maintenance, repair or replacement that may be required within the design life of the structure.

Designing durable timber structures requires consideration of material properties and preservative treatment, assessment of potential hazards and selection of appropriate construction details. Designing for durability is dependent upon two key factors:

the performance requirements of the element or structure
factors affecting durability of the element or structure

For structural design, quantitative data enables designers to reach fairly precise conclusions regarding structural performance. This is not the case with respect to design for durability. However, durability can be assessed by equating required performance levels to available historical and test data and considering the factors affecting durability.

The Design Process is as follows:

1. Determine specific application

2. Estimate required performance by considering:

Required life
Required reliability
Initial versus ongoing cost

3. Determine what hazards, if any, are present

4. Determine the hazard level ("H" level) to be used as a guide

5. Develop specifications and details to satisfy the above by considering factors affecting durability of timber components

6. Check against initial performance requirements and refine if necessary.

Reference: Timber Datafile P4 – Timber – Design for Durability of the NAFI Timber Manual.