OAA Rain Penetration Control Practice Guide:
EIFS Interpretation Bulletin (Exterior Insulated Finish Systems)

To support the change in coverage for rain penetration of certain exterior wall systems of the Pro-Demnity Insurance Company’s Professional Liability Insurance Policy, the Ontario Association of Architects (OAA) released the OAA Rain Penetration Control Practice Guide (Guide) in July of 2002. Questions regarding the interpretation of the Guide have been directed to the OAA, especially with regard to Exterior Insulation Finish Systems (EIFS). This Bulletin is intended to address these questions. The Guide contains 2 pages of text (pp. 23 and 24) that relate directly to EIFS, and these pages should be reviewed. Note, however, that the minimum standards applied to EIFS cannot be understood without reading the entire Guide.

Need for Drainage

The exclusion in the policy states that it excludes claims arising from the ingress of rain for walls that have “no provision for drainage of precipitation that penetrates the wall system, or as otherwise provided in Practice Bulletins by the Association”. This has been improperly interpreted by some to mean that all wall systems must be drained systems. This is not the case, since the reference to the Practice Bulletins allows for other approaches. The Guide provides several examples of alternative solutions, and expressly shows example details of EIFS and precast concrete solutions that are not drained systems. The Guide also expressly states that face sealed (FS) systems over moisture sensitive substrates (such as gypsum) are not insured.

In almost all cases, a Dual Barrier / Drained Joint (DB/DJ) system over glass mat faced exterior gypsum will meet the requirements of the guide and ensure coverage. On the condition that good detailing and adequate general review of construction is provided, the DB/DJ approach may be used even in high-rise applications. The secondary barrier may be a proprietary trowel applied product or other types of water proof membranes.

As stated in the Guide, if EIFS is applied over concrete or concrete masonry substrates, a face sealed approach is acceptable in the field of the wall (since these substrates are water tolerant), but all joints and penetrations must be drained (e.g., a FS/DJ approach is sufficient).

For those who choose to use drained EIF systems, drainage openings at the base and intermediate horizontal penetrations (movement joints, window heads, etc.) must be provided. EIFS manufacturers typically have special details for each of their particular systems and conditions.

Joints. The Practice Bulletin does require all joints and penetrations (e.g., windows) to be drained. Numerous detail drawings are provided in the guide to assist EIFS designers with means to achieve this (e.g., Figure 20, p.25, Details 2 through 10, 13).

A drained joint (sometimes called two-stage) is not always created by two lines of sealant. The inner seal is often achieved by a water resistant barrier, flashing, or gasket, as it is in window-to-wall joints, prefabricated panel systems, etc. The outer seal may also be provided in the form of gaskets, labyrinth joints, or similar, although this is almost never the case for EIFS.

Quality Classes. These classes, as used in the Guide on page 24, apply to the level of assurance that a designer can have that a functional system will be installed. The intent of the table was not to require strict interpretation, as it was presented as only a recommendation. The description of the quality classes was not intended to require all of the listed elements, but to provide examples for what constitutes a high degree of reliability in the process. For example, the designer may be comfortable with the decision that Class 1 is applied to once a week reviews for a relatively simple job with an experienced crew. Similarly, prefabricated panelised systems often have high levels of quality control and may be deemed by the designer to be a Class 1 system. The table on page 24 is intended to alert designers to the fact that a number of factors should be accounted for in the choice of the best system for their project.

Scope

The scope of the Guide does not include many other requirements of a wall system. For example, impact and fire resistance; proper mesh embedment and base coat thickness; sealant selection; insulation type; air barrier system detailing; thermal bridging; structural deflections and building movements; movement joint design and spacing; and finish colour and texture, are all important considerations necessary for the successful design of any enclosure wall system, including EIFS.

EIFS, as described in this bulletin and in the Guide, is a system of various components that work together in a particular way. Changing one or more of the components can affect the nature of the system and its performance. The general attributes and performance of the system, as described, may no longer apply. Care and professional judgement should be taken in such situations.

Canada Mortgage and Housing Corporation (CMHC) is expected to release a Best Practice Guide for Exterior Insulation and Finish Systems that will cover all of these topics in some detail.