SOURCES AND EFFECTS OF WATER AND MOISTURE DAMAGE
– Moisture trapping: usually the consequence of poorly planned site moisture management or poor workmanship (eg installation of impervious membranes onto wet timber substrates). These wetting mechanisms can be triggered by a variety of sources at different times during the life of a timber building 7 . In terms of the consequences of water exposure, different timber products and assemblies absorb and dry at different rates; wood species, end-grain exposure, surface treatment and the presence of hidden voids have a huge impact on the overall behaviour of a timber structure 8 . Exposure to high levels of moisture during construction can cause delays to follow on works and problems later down the line, from localised surface discolouration, corrosion of metal fasteners and dimensional changes (eg shrinkage/swelling) to fungal decay (in a trapped water scenario). However, most of the issues that arise during construction are short term and can be easily avoided with a comprehensive moisture management strategy and
A timber structure can become wet by four main mechanisms:
– Infiltration: the development of a gravity fed water path arising from infiltration of water. This typically originates from the roof or foundation of the building, from cladding panels on the façade, from leaks (escape of water) in the plumbing system or from the activation of a sprinkler system. – Capillarity: movement of water within the wood itself. This occurs mainly where the wood touches the ground or is wet from precipitation, especially in the end-grain areas of columns or wall panels. – Condensation: occurs when moist indoor air meets a cold surface and condenses into droplets (thermal bridging); poor building envelope (airtightness) is also a potential cause of condensation.
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Roof Wall base Service locations
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Façade 4
Figure: Main risk areas in a timber building
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DURABILITY
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