ABSTRACT

In the late 1980s and early 1990s, buildings with face-seal Exterior Insulation Finish Systems (EIFS) were subject to some highly publicized rainwater penetration problems. This greatly diminished the acceptance of EIFS as an appropriate cladding system, particularly in exposed walls in climates with high levels of rainfall.

One industry response was the development of drained EIFS in which there is a second, internal plane of moisture protection and a system to provide drainage, back to the exterior, of moisture that enters the cladding. The design of these systems had to balance a number of performance requirements. These include:

• Minimizing rainwater penetration into the system
• Providing a layer, internal to the system, that provides a sufficient level of resistance to capillary transport of moisture to act as the secondary plane of moisture protection
• Providing a material layer (usually the same as above) that offers a sufficient level of resistance to air leakage to act as an air-barrier, and perhaps, offers a sufficient level of vapour resistance to act as a vapour barrier
• Providing clear drainage paths of sufficient size and coverage to encourage drainage rather than capillary retention of incidental water that does enter the system
• Designing the internal drain paths in a way that minimizes air flow that could compromise the effectiveness of the insulation
• Providing the required fire resistance for the application 

A number of manufacturers developed proprietary systems using variations of these concepts. Drained EIFS employ fundamentally different design principles than face-seal systems and so detailing is different and in many ways more complex.

The authors have had the opportunity of being involved in the design and construction review of several projects where drained EIFS of different types and manufacturers were installed on mid- and high-rise residential buildings. This paper discusses circumstances where detailing challenges were encountered and how focus on such fundamental design principles as deflection, drainage through gravity and capillarity break were used to resolve them.