Condensation in Buildings - Australian Building Codes Board

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Information Handbook: Condensation in Buildings 2.1 Overview – Summary: • Water vapour laden air circulates freely through virtually all parts of buildings and even a low concentration of water vapour can be too much when building surfaces are too cool. • High relative humidity indoors and in the building fabric can cause health risks and material damage before any condensation actually occurs. • Risks begin with the local climate but can be fundamentally altered between seasons when artificial cooling is used. • Effective designs for building envelopes must control the movement of water, air, water vapour and heat into and through the building fabric. • When a building is in use, limiting the accumulation of water vapour requires attention at its sources and to effective ventilation. • The design and detailing of new buildings to manage the unavoidable presence of water vapour must take account of regulatory provisions and may benefit from risk analysis methods and supporting information set out in international standards. DRAFT HANDBOOK Australian Building Codes Board Page 11
Information Handbook: Condensation in Buildings 3 Water Vapour 3.1 Water Among commonplace substances, water has the unique ability to be a solid, a liquid or a gas at ordinary temperatures. Figure 3.1 shows that it can change from any one form directly to any other. Possibly the most exploited of these transformations is the evaporation of liquid water into its gaseous form of water vapour. We rely on evaporation, consciously or not, for drying almost everything that has become moist, damp or wet. When the same process reverses, and water vapour cools enough to condense into droplets of liquid water, the results are often unhelpful. Figure 3.1 – Possible changes between forms of water at ordinary temperatures Sublimes to water vapour Freezes to frost SOLID VAPOUR Freezes to ice Melts to water LIQUID DRAFT HANDBOOK Mist on a bathroom mirror is inconvenient but a slippery film of condensate on a tiled floor can be dangerous. Similar condensation, concealed from view inside the assemblies of materials that form the building enclosure, can accumulate into problems of water leaks, corrosion, decay and microbial hazards. Condensation in difficult places can happen because water vapour has the mobility of a gas and the versatility to revert to a liquid in parts of the building enclosure that water would not be expected to reach. Condenses to dew Evaporates to water vapour Australian Building Codes Board Page 12
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Condensation in Buildings - Australian Building Codes Board

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