Mold risk in cavity

[Sandberg]

Hello,

I have to assess the risk of mold growth within an interior cavity. The wall assembly is:

1. painted render
2. 580 mm historic brick masonry (modelled as 20mm + 560mm)
3. 80mm cavity (modelled as 1mm "80mm air layer" + 78mm "80mm air layer without additional moisture capacity" + 1 mm "80mm air layer")
4. 75 mm Isover mineral wool (modelled as 1mm + 74 mm)
5. Smart VCL intello
6. Plasterboard

To assess the mold risk within the cavity, I have assessed the moisture content within the 2 materials adjecent to the cavity (masonry and mineral wool): the RH is never at 100%, the moisture content increases briefly within the first months but then it decreases steadily afterwards, the moisture content within the mineral wool is well below the free saturation point. However the RH in the two thin air layers is above 80% for the first two years. Is this a risk factor for mold growth? How should I intepret the 80%RH? Is it a risk only if it causes condensation in the adjecent materials, which in this case does not happen?

[Daniel]

Hello Sandberg,

the 80 % RH are related to a temperature of approx. 12.5 °C (at indoor climate of 20 °C and 50 % RH). At lower temperatures thatn 12.5 higher RH values are necessary for mould growth. But normaly lower limits apply then condensation.

In a first approach you can use the Isotpleth Evaluation in WUFI. However, this is pretty on the safe side for interior insulations. However, if it works, it is OK. If not, mould growth can (at least accoring to WTA 6.4 and 6.5) be avoided by excluding flow of interior air behind the insulation system. Therefore it would be cleraly better to have the cavity on the warm, not on the cold side.

best regards
Daniel

You can find some more information here: https://web.ornl.gov/sci/buildings/2016 ... l_Pred.pdf