Our moisture calculations are a more detailed and accurate assessment of heat and moisture transfer and will eventually replace the Glaser Method (based on ISO 13788), a standard static interstitial moisture calculation.
The calculation process is a complex one-dimensional, finite element, heat and moisture transfer model (HAMT) simulating the movement and storage of heat and moisture in surfaces simultaneously from and to both the internal and external environments.
As well as simulating the effects of moisture buffering, HAMT is also able to provide temperature and moisture profiles through composite building walls and help to identify surfaces with high surface humidity.
Below is a step-by-step overview of the inputs required for our moisture simulations. All inputs are based on DA07 Criteria for Moisture Control Design Analysis in Buildings, in line with National Construction Code 2022 requirements.
Run Period – The default Run Period for moisture simulations is 5 years. Water Content should stabilise yearly or decrease over time within a well-performing wall system. If any Water Content or Mould Growth Report increases year on year within any results, the Run Period should be increased until any year-on-year increase stop.
Included Reports – Dew Point, Water Content, Mould Growth and Relative Humidity are all set by default and can be turned off as required. Once a simulation is complete, the results will be post-processed and presented against DA07 requirements.
Orientation – the ‘worst-case’ orientation is typically assessed based on its drying potential. This is typically the non-equatorial facing orientation.
Cavity Ventilation Rate – The Cavity Ventilation Rate impacts the boundary material drying potential. Defaulting to 35 ACH to represent a masonry wall system (ventilated at the top and bottom of the wall – every 5th perpend opening), Cavity Ventilation is complicated and should always be conservatively nominated. If you are unsure, we recommend speaking to a supplier or facade consultant to resolve the ACH value or set it to zero.
Floor Area – The Floor Area (m²) is nominated for the space applicable to the study. This is typically the entire space. For example, within a home, this would be the combined floor area of the entire home.
Floor to Ceiling Height – The Floor to Ceiling Height is used to determine the volume (m³) of the study and the resultant moisture generation rate as per the DA07 intermediate method. It can be assumed to be the average height, where variable heights are within the study.
Surface Resistance – Surface Resistance determines heat transfer coefficients (W/m²) and defaults to HAMT (Modelling) generic values. These are usually lower than those used in System R-value calculations. Typical surface resistances from System R-value calculations can also be adopted as Per System R-value calculation.
Specify Temperature – Indoor Temperature (°C) defaults to 21 °C, as per DA07.
Specify Relative Humidity – Indoor Relative Humidity (%) is set to off as it is typically not controlled in buildings. When toggled on, it can be controlled as a constant value.
Air Changes per Hour - Air changes per hour the rate at which outdoor air replaces indoor air. A default value of 0.2 is nominated based on DA07. A higher value can be adopted based on a known building envelope and ventilation strategy. Note, ASHRAE Standard 62.2-2016 recommends that homes receive 0.35 air changes per hour.
Relative Humidity Mode – The Intermediate Mode is nominated by default, as per DA07. When selected, Indoor humidity is determined from the weather file and HVAC equipment profile.
Indoor Typology – Residential is set as default. Commercial settings will be made available in late 2022.
Moisture Generation Mode - Moisture Generation (kg/s) is adopted by either the number of bedrooms or people or as a custom value. The generated value is then added to the volume (m³) for partial diffusion through the study wall.