WUFI: Hygrothermal Analysis Software

By: Cassie Park, PE

Computer-aided Hygrothermal analysis and modeling allow us to understand movement of heat and moisture through building components. While such analysis is critical when developing a new building, it is also an effective tool in the repair industry when building owners are considering new roofing systems, re-cladding/coating building facades, or even introducing interior finish treatments.

When changing the cladding system components or interior conditioning system of the building, it is always important to understand how heat and moisture will move through the building envelope to ensure the new system can achieve long term durability and satisfactory performance. Concerns such as condensation, material degradation (rot, spalling of concrete/brick ,etc.), or even mold growth may result if the building envelope is not properly designed with the overall system drying potential and wetting risk being considered.

Unfortunately, modeling and analyzing heat flows and moisture drive is a very complex task. Lucky for us, we have the software that can help: a relatively new software family called WUFI (Wärme und Feuchte instationär, or Transient Heat and Moisture), developed by the Fraunhofer Institute for Building Physics (Germany) and Oak Ridge National Laboratory (US). This software calculates heat and moisture transfer through a selected portion of the building envelope (wall or roof section), in accordance with algorithms set forth in ASHRAE 160 “Criteria for Moisture-Control Design Analysis in Building.” The program can adequately model a component of an existing structure by taking into account the material properties, orientation of the analyzed section, and historical climate data for the location of the structure.

From this modeling, we are able to analyze:

• How moisture will accumulate or dry out of a wall system over time;
• Which layers of the wall system are most susceptible to moisture accumulations, and thus damage or decay;
• How temperature and interior relative humidity may fluctuate based on historical climate information for the region; and
• If a potential risk of biological growth (i.e. mold) is present on interior finishes.

If you are considering a substantial change to your structure or fear you’re experiencing a moisture/heat related issue, obtaining a WUFI simulation should be considered to protect your investment!