4 . 1
MOISTURE AND DURABILITY
Durability is generically defined in ISO Standards as “the ability of a constructed asset or any of its components to perform its required functions over a specified period of time without unforeseen maintenance or repairs” 1 . In simple terms, durability defines the longevity of a material or product. Any material used in a building should ideally be as durable as the building itself, typically 50 years, which is the medium working life of a typical structure (as defined in Eurocode EN 1990). Most timber products refer to working and service life in their European Technical Assessment (ETAs) and Environmental Product Declaration (EPDs). In the context of timber and engineered timber products, durability also pertains to their resistance to moisture induced mould or fungi, specifically in regions of temperate climate.
A typical design team should keep account of buildability, cost and time/programme implications but also adopt the following durability measures: – Identify areas of risk and predict potential weak points and damage level. – Mitigate damage with a coordinated risk management plan. – Be aware of damage repair measures (remediation). As further discussed by the STA: “the industry does not establish roles and responsibility for durability, leading to confusion and ignorance of moisture management in the process of commissioning a new building” 2 . It is imperative for these responsibilities to be clearly defined for each project workstage to preempt any potential durability related issues. There are other durability concerns for timber, such as insect infestation, but this piece of research focuses solely on issues related to water and moisture, as these pose the most significant risk to timber buildings. Other than structural errors, approximately 90% of all building construction problems are associated with water in some way 3 .
Overall, the durability of a timber building is most affected by:
– Moisture (in its various forms). – Incorrect specification of the material for its given environment. – Incorrect detailing, installation and maintenance procedures.
Common Perception: Timber buildings will always decay and so have a short useful life. Reality: Properly designed, constructed, and maintained timber buildings can be just as durable as those made from steel or concrete. When moisture is managed effectively, timber can last indefinitely.
Long-lasting durability is a function of:
– An environment where temperature and humidity, the main variables of timber’s moisture content, are given proper recognition (Service and Use Classes). – A correctly specified material. – Correctly carried out design, installation, maintenance (and possibly replacement procedures).
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DURABILITY
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