Balancing the Control of Heat, Air, Moisture, and Competing Interests

This paper draws on one rehabilitated wall assembly with high humidity levels to explore the assumptions and decisions faced by the design team when completing a rehabilitation project with respect to controlling heat, air, moisture and the resulting affect on building performance. Decisions and assumptions discussed include:

• Indoor environment: acceptable and assumed ranges of conditions for temperature, ventilation, moisture generation, and the resulting balance relative humidity.
• Cost and existing construction: constraints of the existing construction including wall dimensions and the cost of rehabilitation.
• Current norms for building design and construction: current accepted norms for the control of heat, air and moisture transport and the importance of balancing these controls.

This paper presents a combination of calculated values for the indoor environment using a moisture balance between the exterior and indoor environment, HAM computer modeling, and field measurements of a rehabilitated project to support this discussion. Conclusions and recommendations are drawn from the lessons learned from completing this work.

Authors: Mark Lawton, P.Eng., Patrick Roppel, M.A.Sc, P.Eng., Brian Hubbs, P. Eng.
Date Published: 2007