How does WUFI work?

As the popularity of WUFI increases and we are getting more and more inquiries, it’s important that our clients understand what it is and how it works


WUFI® is an acronym for Wärme Und Feuchte Instationär—which, translated, means heat and moisture transiency, also known as a hygrothermal analysis.   WUFI® software uses the latest findings regarding vapor diffusion and moisture transport in building materials and assesses mould growth risk by modelling the layers in a construction build up and assessing where moisture may get trapped.  Mould typically occurs in structures because they can’t dry out.  It doesn’t really matter how wet a building structure gets, as long as it can dry out.  As building codes change and energy efficiency and air tightness requirements increase, building our wall, floor and roof cavities the way they’ve always been built may present moisture problems over the long term and this is why a WUFI risk assessment is such a useful tool.  

Why would I ask for a WUFI assessment?

The purpose of WUFI is to assess the mould risk in your project, primarily the risk of what’s called “interstitial” mould.  This is the mould that appears within your wall, roof and floor cavities.  This mould usually grows over a period of years (although it can happen within months) and you may not be aware it’s even happening.  A bit like termites, you might not know you have a problem until you start to notice musty smells and cannot figure out where they are coming from, or until you decide to undertake a renovation and as you remove internal and external claddings, you discover mould growth or deterioration on your structure (See Image 1).  This type of mould growth in your home can result in allergic reactions such as sneezing, a runny nose, red eyes and skin rash. Moulds can also cause asthma attacks and for some who are particularly sensitive to mould related illnesses, the health impacts can be more serious.  In addition, let’s not underestimate the mental health impacts of the strain these types of chronic illness can have on a family as well as the financial burden of rectifying the mould.

Image 1 – Mouldy frames behind vapour impermeable a membrane

If the structure of your home is compromised through mould or damp, the cost and inconvenience of repairing your (very likely) most expensive asset can also be extremely stressful.

If you are asking for a WUFI assessment you will most likely fall into one of the following categories:

  • You are a builder or architect wishing to avoid legal liability for designing or building a mouldy building; or
  • You are a well invested and well researched home owner wishing to avoid the above problems in your new home.

WUFI 1D or 2D?

We have the capacity to both WUFI 1D (Image 2) and WUFI 2D (Image 3 assessments – for 99% of situations, WUFI 1D will be sufficient.   WUFI 2D is considerably more complex and time consuming and thus, should be used as a complementary simulation to 1D in specific circumstances, rather than an alternative.

Image 2 – WUFI 1D Simulation – simple geometry       Image 3 – WUFI 2D Simulation – junctions, corners etc

Does WUFI assess a house as a whole building?

No.  WUFI assesses details only, for example a specific wall, roof or floor build up.  We have indicated below in Image 4 with blue rectangular boxes an example of the cross section locations of what we would assess.  Each of these blue highlighted areas would be a separate simulation.  WUFI does not have the capacity to assess the mould risk for a house as a whole building.

Image 4

At each of these cross sections, the critical point we assess for mould risk in the construction is interior to the primary water control layer or the interior surface of the water control layer.

What are the steps in a WUFI assessment?

  • We receive your plans
  • We establish exactly which parts of your building you would like assessed
  • We provide a fee proposal for the scope of works agreed on
  • If you accept our fee proposal, we will gather the information we require from you to complete an assessment as accurately as possible e.g. location, house volume, moisture load, detailed material data etc
  • We will provide you with a report with a brief discussion of the construction and a mould index of each assessment.

What does the Mould Index mean?

WUFI uses climate data as well as project specific information to assess risk in accordance with AIRAH DA07 Criteria for Moisture Control Design Analysis in Buildings.  WUFI results come in the form of a Mould Index from 0 to 6.  A description of what each level means is in Table 1 below.  These results also come in the form of a simple stop light system.

Red = High Risk  Amber = Medium Risk  Green = Low risk

Table 1

What happens if our assessment has an amber or red result?

We will work with you to create a Low Risk solution as far as is practical for your project.  This may require product substitutions or changes to construction details.  There may be some parameters that we need to work around such as cost or practical restraints that are specific to your project and therefore it is important to note that it may not be possible for us to assist you to reduce the mould risk of your construction.  Additional costs may apply.

If you would like to learn more about the mould risk in your project, please get in touch.

Jessica Allen

0409 404 924                                                                                                                                                                                                                                                                                                              


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