All buildings, regardless of material used, will develop moisture or water related issues at some point in their life. This can include the corrosion of metals, loss of bonding between the steel and concrete in reinforced concrete, damage to plasterboard through dissolution, cracking of masonry and concrete caused by freeze-thaw cycles, and the decay of wood-based materials 4 .However, timber is more susceptible to this type of damage because it is both hygroscopic (porous) and anisotropic, meaning it has different material properties in different loading directions. Regardless, a properly designed, constructed and maintained timber building will last a long time. Moisture is not a risk to timber so long as it can dryout, however timber tends to get wet faster than it can dry. If it is exposed to water for a long time, it will absorb it and become saturated, leading to issues including staining, mould growth, dimensional changes, and eventually decay; the severity of which is proportional to the duration of exposure and the moisture content 5 .
This is important for designers, contractors and insurers because in modern timber structures, particularly office buildings, timber is often left exposed, making even minor imperfections in the timber unacceptable. These issues can be prevented by understanding the properties of wood and implementing a comprehensive moisture management strategy throughout the entire lifespan of a timber building. While it is widely recognised that the construction phase carries a high risk of water damage, the occupation phase—where water leaks or ingress can also cause significant damage—is often overlooked. To increase a building’s resistance to moisture damage and extend its lifespan, it is important to consider durability from the early stages of design through construction and handover. This includes implementing risk mitigation strategies as well as planning for repair and maintenance.
VARIABLES INFLUENCING BEHAVIOUR
PROPERTIES
Hygroscopic (takes on and releases moisture from/to surrounding environment)
Loading (duration, history and direction)
Moisture content (MC) (level, variations, exposure length)
Anisotropic (different material properties in different load directions)
TIMBER T IMBER
chVaiscoelastic (presents both plastic and elastic chracteristics when exposed to a certain deformation)
Temperature (T)
Elasto Plastic mit case of viscoplasticity (eg permanent deformation)
Relative Humidity (RH) of the surrounding air
li
Figure: The effect of environmental variables on timber
DURABILITY
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