Moisture problems in the cavities of exterior walls and roofs are often caused by the exfiltration of humid indoor air. Serious building envelope problems can result from moisture condensation within exterior walls and roof assemblies. They include efflorescence on brick and stone, spalling of brick and stone, corrosion of anchors and brick ties, paint peeling, icicles on the exterior facade, the rotting of sheathing and wood framing, the production of mold and mildew and more. Indirectly, it also causes increased rain penetration, high energy costs and low ind oor humidity in winter.

The moisture problems occur when the humidity of the exfiltrating air condenses in a construction cavity, most often on the backside of a sheathing or cladding. The cause of this condensation can be prevented or at least controlled by the installation of an air barrier system, by limiting the indoor relative humidity level in winter and by balancing the building pressure through its ventilation systems. This article examines the problems of air leakage control, the concepts of air leakage paths and air pressure differences, the design requirements of air barriers systems, the properties of air barrier materials and systems, the building code requirements, the design of air and vapour barriers. It also provides notes on the preparation of drawings and specifications and site review considerations.

• air barrier
• ventilation: airtightness, air leakage,

1. Basics of Noise Control
2. Building envelope design using metal and glass curtain wall systems
3. Glass and Aluminum Curtain Wall Systems
4. On-site exterior wall monitoring methods for air leakage, condensation and rain penetration control problems
5. The rainscreen wall: a commissioning protocol  

1. Rain penetration and moisture damage in residential construction