Why evaluate hygrothermal performance?
Calculation of thermal performance is common practice for evaluating heat loss through building components. For many build-ups, and especially in retrofit projects, insulating to low U-values brings hygrothermal challenges that haven’t been generally acknowledged or understood. In this context, it is critical to evaluate moisture conditions over time, so as to assess the risk of moisture accumulation. Permanently increased moisture content in building components may result in reduced thermal performance, structural decay, and even health risks due to mould growth.
A hygrothermal performance assessment can evaluate the robustness of a design, building or building system, ensure long-term health of occupants, assure compliance with Building Regulations, identify future weaknesses, and therefore lead to significant cost savings in the life of the building.
Glaser method vs numerical calculation
The Glaser method (under I.S. EN ISO 13788) has been (and still is) widely used to assess risk of interstitial condensation. It is a simplified, steady-state method assuming that moisture transport is by vapour diffusion alone. It doesn’t take account of capillary transfer of liquid water, moisture storage capacity of materials, driving rain, construction moisture, solar radiation and other important phenomena. Therefore, following the scope of its own relevant standard (I.S. EN ISO 13788), the Glaser method is not suitable for assessing components where the effects of the above mentioned phenomena are not negligible.
Numerical hygrothermal simulation (under I.S. EN 15026) provides far more reliable information on the risk of moisture problems within building components and on the design of preventive or remedial treatment.
Why can Wufi do?
Wufi is a menu-driven, user-friendly software developed by the Fraunhofer Institute for Building Physics (Germany) and validated using data derived from outdoor and laboratory tests. It allows numerical calculation of transient hygrothermal performance of building components, exposed to realistic climate conditions.
Wufi can be used for assessing:
· the risk of interstitial condensation
· the risk of moisture accumulation from driving rain
· the risk of mould growth
· the risk of rot or corrosion in structure
· the risk of freeze-thaw damage
· the hygrothermal effect of retrofit measures
· the time required for construction moisture to dry out in masonry walls
· the moisture performance of roof and wall build-ups under unanticipated use or in different climate zones
Wufi can also be used as a teaching aid or advertising tool because of the strong visual aspect of its calculation results.
Proper application of Wufi requires training and experience in the field of building physics. It is primarily aimed at building fabric consultants, architects, engineers, manufacturers of building materials, and other building professionals.
Information about different versions of Wufi can be found in this flyer.