Mold and formation risk according to EN ISO 13788:2013. Here is how to evaluate the risk situations that could generate mold formation

The formation of vapour inside building structures is a very complex process.
For a proper study of this phenomenon, we need to look at the following aspects:

  • The mechanisms that cause the process to arise;
  • The material properties;
  • The initial and boundary conditions.

The EN ISO 13788:2013 standard analyzes the critical surface moisture problem, which can cause the formation of mold on the interior surfaces of buildings.
Let’s see the calculation procedures that determine the internal surface temperature of building components: below this temperature there is a high probability of mold formation.

Mold-formation risk assessment: Calculation procedure

In order to proceed with a correct mold formation risk assessment, the following aspects must be considered:

  • building materials and product properties;
  • the building location;
  • monthly frequency for climatic data:
  1. external temperature;
  2. external humidity;
  3. indoor air temperature;
  4. internal humidity;
  5. heat transfer;
  6. water vapour transport.

Mold formation risk assessment: surface temperature calculation

To design the building envelope so as to prevent the negative effects of relative critical humidity at surface level, for example the formation of mold, the first thing to do is calculate the surface temperature.

There is a risk of mold formation for relative surface moisture (φsicr) greater than 0,8.
In fact, the main design steps are represented by:

  • calculation of relative humidity of indoor air;
  • calculation of the acceptable value of the saturated volumetric humidity or the saturation vapour pressure on the surface based on the relative surface moisture required.

This allows us to determine:

  • the minimum superficial temperature;
  • the “thermal quality” of the required building envelope.

Mold growth is however influenced by another three parameters:

  1. The “thermal quality” of each element of the building envelope, represented by thermal resistance, thermal bridges, geometry and internal surface thermal resistance. The thermal quality can be characterized by the temperature factor on the inner surface, known as fRsi;
  2. indoor humidity production pi;
  3. indoor air temperature and heating system θi.

Mold Formation Risk assessment: a calculation example with the use of specific software

Below is an example of numerical calculation of energy transmitted through building structures affected by thermal bridges.

The Report also shows a verification on the mold growth risk formation, carried out using the TerMus-BRIDGE software solution by ACCA software and in this respect, TerMus-BRIDGE allows you to evaluate the risk of mold formation according to the EN ISO 13788 standard.

For the mold formation risk assessment, the following are defined:

  • the minimum surface temperature on the inner face;
  • the critical temperature;
  • the critical temperature factor fRSi (max),
  • the critical month.

Once the calculation process has terminated the thermal bridge is then analyzed to see whether it is subject or not to the risk of mold formation.

Download the example of Technical Report in English made with TerMus-BRIDGE

Click here to find out all the features and download TerMus-BRIDGE, the Thermal Bridges Calculation Software