Condensation in Buildings - Australian Building Codes Board

Information Handbook: Condensation in Buildings
6.6 International Standards
There are a number of international standards available that provide details on moisture control
and condensation risk assessment in buildings and building envelopes. The assessment
methods are mostly based on multi-variable calculations and enacted through computer
simulation tools. The summaries below describe the scope of some of these standards and
outline the nature of their content.
ASHRAE Standard 160-2009 Criteria for Moisture-Control Design Analysis in Buildings
For United States conditions, ASHRAE Standard 160-2009 seeks to provide a consistent
framework for design assumptions or assumed “loads” when using computer simulation tools to
predict thermal and moisture conditions in buildings and the building envelope. The Foreword
notes that “computer models are increasingly used to make recommendations for building
design in various climates [but the] results obtained with these models are extremely sensitive
to the assumed moisture boundary conditions”. It also records that development of the standard
“pointed to many unanswered questions, questions that hopefully will be addressed and
answered by research in the near future”. ASHRAE Standard 160 is termed “a national
voluntary consensus standard”.
The content of ASHRAE Standard 160 covers the minimum acceptable criteria for selecting
analytical procedures, inputs to those procedures (design parameters), the evaluation and use
of the outputs and comprehensive reporting requirements. These requirements are elaborated
below:
Criteria for selecting analytic procedures
The ASHRAE Standard 160 requires the use of a transient analytic procedure with a maximum
time step of one hour. To comply with the Standard, the procedure must be able to calculate:
• the transfer of heat energy through the building fabric, including the temperature effects
caused by water changing between its solid, liquid and gaseous states (or phases);
• material properties affected by moisture content;
• the transport of water (as liquid or vapour) by capillary suction, deposition on surfaces,
storage in materials, vapour diffusion and by liquid water leakage; and
DRAFT HANDBOOK
• the effects of any ventilated cavity which is included in the design.
In addition to being able to calculate these outputs, the selected procedure must also report the
temperature and relative humidity at each surface and interface between layered materials; the
average temperature of each material layer; and the average moisture content of each material
layer.
It is important to note that current transient analytic tools, including the pre-eminent WUFI (from
the Fraunhofer Institute for Building Physics), do not account for heat and moisture effects
caused by air convection through and within building components, limiting the application of this
standard in situations which are not uncommon.
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