Condensation in Buildings - Australian Building Codes Board

Information Handbook: Condensation in Buildings
4.7 Climate in Summary
• Four basic climate types can be enough to categorise the main environmental factors which
affect human comfort: warm humid climates, hot dry climates, temperate climates and cold
climates (Section 4.1).
• Although the eight BCA climate zones for energy efficiency are variants of the four basic
types, their definition did not depend strongly on the humidity conditions which influence
condensation risk in buildings (Section 4.1).
• Although substantial effort has been made overseas to classify hygrothermal conditions
over broad regions for building design and moisture control and to reach consensus on
appropriate inputs to risk evaluation methods, similar information has not been assembled
for Australia (Section 4.2).
• For a first indication of propensity to outdoor condensation in various places, local building
practitioners can use monthly climate statistics from BOM. Comparing monthly mean
minimum temperature with the average of the 9am and 3pm outdoor dew point
temperatures will highlight months when dew is likely to form on outdoor surfaces and the
intensity of the “risk” (Section 4.3).
• The ABCB has extended the same comparison across the country using gridded data sets
from BOM to prepare a map of comparative outdoor condensation risk (Section 4.3).
• A more comprehensive view of climate characteristics in any one place can be assembled
on a psychrometric chart using the same BOM data. The resulting chart can indicate
seasonal patterns in temperature and humidity, likely periods of demand for heating and
cooling and the extent of outdoor condensation over all 12 months (Section 4.4).
• For assessing condensation risk, indoor conditions can be considered as a distinct climate
system due to the presence of indoor sources of water vapour and intentionally created
temperature differences. Indoor water vapour levels are strongly influenced by outdoor
conditions, ventilation levels and the management of indoor water vapour sources (Section
4.5).
• Despite differences in outdoor climates between geographic regions, the impact of a typical
residential indoor climate on absolute humidity does not vary substantially between
locations. Adjusting the absolute humidity used to assemble the charts discussed in Section
4.4 can highlight whether there is a potential for condensation or excessive relative humidity
in the cooler parts of the building fabric when indoor water vapour finds its way there
(Section4.6).
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