1. Improving Building Hygrothermal Performance through Advanced Application of Building Materials: a Holistic Approach towards Mould Growth Prevention
Marcela BRAUNER , John E. TOOKEY , Ali GHAFFARIANHOSEINI
AUT University, Auckland, New Zealand,

2. Moisture related issues
high or extremely low indoor relative humidity (RH)
thermal – hygrothermal bridges
condensation on interior surfaces or inside of the construction
mould growth
dampness
deterioration of construction materials or structure
frost damages
low quality of indoor air
This research based on extensive literature review on building hygrothermal performance, moisture buffering materials, and mould growth aims to overview the consequences of underestimating or neglecting hygrothermal relations in buildings.

3. Hygrothermal building performance
Nothing last for ever

4. Condensation and mould growth
vapour pressure ≥ vapour saturation pressure
dependent on:
indoor temperature
indoor relative humidity (RH)
outdoor temperature
thermal resistance of the weakest element in the building envelope
Mould growth:
long lasting excessive moisture
biological deterioration of building components
Temperature falls below the dew point
Mould growth is a significant sign of long lasting excessive moisture and biological deterioration of building components.

5. Solution
Ways of controlling RH fluctuation and their impact on the energy consumption:
reduction of RH under a critical level of 70%RH
right relations between moistening and drying
passive and active control of RH of the indoor air
purposeful usage of hygrothermal characteristics of materials
- essential are the right relations between moistening and drying

6. Building materials and moisture buffering
building materials and finishes which have the ability to absorb moisture and quickly dry out when the RH drops
crucial the following factors:
interior materials with high moisture buffering capacity
sufficient depth and area of hygroscopic materials
diffusion open surface protection
fast drying potential
sufficient ventilation
Insulation
air-tightness
minimisation or elimination of thermal bridges

7. Questions How high are the moisture loads into the wall?
Is the drying process possible?
How long would take the drying out? (wetting x drying cycles)
Is the wall construction diffusion open?
How does the construction perform on the long term?
Is there any risk of additional wetting of the wall from driving rain or melting of frozen water?
By consideration and calculation of the building envelope is the building hygrothermal performance very important. Following questions have to be answered:

8. Building envelope Building Envelope
Description: in buildings it is a divergently permeable structure depending on the outer wall design
Location: outer boundary
Function: protects and controls what goes in and out of the building
Source: Phoebe Hancock, SlidePlayer.com

9. Holistic approach to design process
Decisions based on the climate specific design principles
orientation of the building, insulation, fenestration, air- tightness, need for heating and cooling, mechanical ventilation, shading, and thermal mass
Determination of building materials
exterior walls - respect the outdoor situation to achieve energy efficiency and hygrothermal performance
interior walls and ceilings - moisture and thermal buffering
Optimisation process using simulation tools
energy simulation (EnergyPlus)
hygrothermal simulation tools (WUFI Plus)
biohygrothermal modelling (WUFI Bio)
Different outdoor conditions and the intended use of the building require divergent construction concepts to achieve energy efficiency, healthy indoor environment, and durability of the building.
to minimise the risk of condensation and mould growth

10. Conclusion
Test houses