ALF help

Design help

On the Design pages you enter information about the particular house design and location to perform an ALF analysis on it.



Previous versions of ALF did not explicitly evaluate benefits other than in terms of heating energy efficiency. However there are several other advantages linked to good thermal design, one of which is improved moisture control. The inclusion of a Moisture Calculator in ALF 3.2 is seen as a way to provide a means to assessing what, if any, rooms in a building will suffer from internal moisture problems serious enough to give rise to mould growth.. Using the calculator, any problem areas can be identified during the early design phase. This will provide the impetus to address the issue early and remove its underlying cause or causes. The calculator is an optional extra for those interested in improving the indoor environmental quality of a new dwelling.

The moisture calculator was produced by Malcolm Cunningham with funding from the Department of Building and Housing as a possible verification method for compliance with document E3 Internal Moisture.

return to top

The Moisture Calculator

  1. Mould growth occurs on walls and ceilings under two different conditions: firstly, where moisture actually condenses a surface, e.g. bathrooms or kitchens; or secondly where wall relative humidities are very high even though condensation does not occur, e.g. bedrooms.

The ALF 3.2 Moisture Calculator works by computing the temperature difference between the inside and outside surface of a room’s walls and the moisture content available in the room. The duration of any condensation that accumulates on wall surfaces and the time it will remain, or the duration of high humidities on the wall, can then be calculated. If this duration of condensation is greater than 3 hours per day, for rooms in which liquid water is produced (e.g. Kitchens and Bathrooms), or high wall relative humidities last for 6 hours or more, for rooms where liquid water is not produced (e.g. Bedrooms); then mould will form on the affected areas.

For rooms with thermal mass temperature fluctuations are smaller and the lag in room temperature change in response to outdoor temperature changes is longer. These effects must be taken into consideration and thus a separate calculation is required.

return to top

Moisture Control Strategies

return to top

Moisture problems in New Zealand houses

Indoor dampness and mould problems are known to be relatively common in New Zealand houses. A telephone survey in 1971 (Trethowen 1972) showed that almost half of homeowners reported problems and that a third of these cases are serious. A summary of the results of this survey is shown in the figure below.

FIGURE: Evidence of dampness in New Zealand houses in 1971.

While there was no evidence of any dependency on particular construction materials, moisture problems were more clearly prevalent in northern regions. Almost 50% of Auckland houses reported dampness problems but the proportion declined to around 40% in Wellington and Christchurch and only 20% in Dunedin. Although few houses were insulated and centrally heated at this time, the results did show that houses rated as comfortable by the tenants, were half as likely to report dampness problems.

A similar trend to a higher incidence of damp houses in northern cities was also seen in a BRANZ house condition survey completed in 465 houses during 1998/9 (Clark et. Al. 2000). Country wide it was estimated that 40% to 50% of houses were noticeably damp during the winter months. This survey was carried out by a trained inspection team and arrived at a similar incidence of dampness to the earlier telephone survey, even though there have been many changes in the intervening 28 years; eg thermal insulation, different house styles, changes in occupancy profiles and dehumidifiers etc. The 1998/9 survey noted that dehumidifiers were becoming quite common and that the incidence of dampness in homes with dehumidifiers was only 25% compared with the national average of 40%. Of the 10% of houses with dehumidifiers, a larger portion (16%) were in homes with unflued gas or portable LPG heating, compared with 7 % in homes heated in other ways. The report also noted that this strategy for dealing with internal moisture did little to correct the underlying causes of dampness and that there may be some linkage in the market between dehumidifiers and unflued gas heating.

return to top


Exterior Wall Length

Interior Wall Length

Floor Area

External Wall Type

Floor Type
Choose whether the room being considered is on the Ground Floor, First Floor and so on. This selection will automatically choose the floor construction type.

Is the ceiling part of the thermal envelope?
Are the heat losses through the ceiling of the room losses through the thermal envelope? If yes; the ceiling area is included in calculating the temperature drop in the room due to conductive losses.

Room air changes per hour
What is the ventilation rate of the room being considered? You may choose to use the default value as set to the building average or input your own if more detailed information is available.

Room Heating
Enter the power of all heating appliances in the room. The power should be in Watts or Joules per second.

The windows connected to this room can be selected from a predefined list automatically created from the ALF window input pages. By firstly selecting an orientation, a list is compiled of all windows selected in ALF on walls of that orientation.

External Construction type
Used to determine the R-value of the coldest part of an external wall or ceiling. This is generally where the framing interrupts the thermal continuity of the insulation. The R-value of thermal bridges can be calculated independently or taken from the drop down list compiled automatically.

Number of adults inhabiting Master Bedroom

Change in one room’s temperature given a 5°C change in another room.
The values set as default here have been chosen as representative of the majority of cases. However if more accurate information is available these figures can be changed.

return to top

 Create an ALF account

Register now to create your free ALF account.

Every user needs to create an ALF account. Creating an ALF account will ensure:

  • Confidentiality for your project.
  • Allow BRANZ to record usage of the ALF tool – BRANZ cannot access any individual projects. Your privacy is assured.

 Contact and Feedback

Contact us at Branz for further information about the ALF 3.2: Annual Loss Factor.