April 1, 2001
by John Straube
EIFS (pronounced “eefs”)–an acronym for Exterior Insulated Finish System–can be defined as a lightweight exterior cladding system consisting of insulation board (expanded polystyrene or occasionally mineral wool) adhered or mechanically fastened to a wind-load-bearing substrate, and covered with an integrally reinforced base coat and a protective surface finish. The EIFS industry is rife with special terminology–some of the most important terms are shown in the figure below.
There are several reasons for the continued growth of the EIFS market: the systems are lightweight and hence impose few structural restrictions on their use; the polymer-based finishes allow for a vast range of colours and textures; the foam plastic insulation used by most systems can be easily shaped to form cornices, reveals, trim, etc.; and the insulation improves energy efficiency by wrapping the whole building in an uninterrupted blanket.
In the past, two broad categories of EIFS were defined based primarily on the type of lamina used: soft-coat/polymer-based (PB) systems and hard-coat/polymer-modified (PM) systems. The former system tended to use thinner lamina, adhesive attachment and expanded polystyrene insulation, while the latter used thicker, harder lamina, often with glass fibre mesh reinforcement, on mechanically fastened extruded polystyrene insulation. The many combinations of systems now available limit the value of such classifications.
The location and manner of construction are also important considerations. Prefabricated or site-fabricated panels, usually with steel backup, are often designed and built in a different manner than field-applied EIFS. An EIF system with a high polymer-content thin (2-3 mm) base coat reinforced with polymer-coated glass mesh, an all-polymer finish coat, expanded polystyrene insulation and adhesive fastening is currently one of the most popular.
The roots of EIFS can be traced to Swedish systems from the 1940s that applied steel mesh reinforced cement-lime stuccoes over high-density rockwool board insulation. The relatively flexible insulation and the mesh reinforcement minimized cracking and wrapped the entire opaque wall in a continuous insulation blanket.
The commercial and technical development of modern EIFS occurred primarily in Germany after World War II. War-related shortages led to the development of synthetic polymers as alternatives to petroleum and natural rubber. Edwin Horbach, a Swiss-trained chemist, is generally credited with implementing the use of polymer-based stucco reinforced with alkali-protected glass fibre mesh over expanded polystyrene insulation. The ability of such a lightweight system to be quickly and easily applied to war-damaged and uninsulated masonry buildings perfectly suited labour- and resource-starved post-war Europe.
EIFS did not become widely available in North America until the oil crisis of the early 1970s. The success of the so-called polymer-based or thin coat EIFS drove the development of a wide range of systems employing a variety of finishes, insulation materials, and reinforcing types. Unlike the moisture-tolerant masonry substrates of Europe, EIFS in North America has been mostly applied over moisture-sensitive substrates of wood and gypsum. Hence, even a small leak could cause serious damage.
As EIFS began to be used more commonly, certain moisture problems were reported, especially in the 1990s. Thousands of Wilmington, North Carolina single-family homes clad with EIFS exhibited serious and well-publicized moisture-related problems. Despite the many confounding variables involved in the problems with these homes, EIFS were often blamed. In most cases problems with EIFS have related to rain penetration, limited drying and inappropriate vapour barriers. These problems occurred because old designs relied on a single barrier exposed to the weather to resist rain penetration. In many cases water infiltrated at face-sealed joints and through-wall penetrations such as windows, decks, and air conditioning units.
Rot and decay of moisture-sensitive substrates has been, and remains, the largest concern with EIFS. However, this can be minimized by the use of proper rain control strategies.
In the last five years, many new EIF systems have entered the market that offer the potential for improved control of rain water penetration. Four classes of rain control design strategy, in order of increasing performance, are commonly available. Face-sealed (FS) perfect barrier systems assume that a perfect barrier to rain penetration is provided at the exterior face (i.e., by the lamina and sealant). Dual barrier (DB) systems assume that the primary face seal may fail, and thus employ a secondary concealed water barrier that covers and protects the substrate. Drained (D) walls assume that the eventual failure of lamina and joints is inevitable, allowing in so much water that a water barrier (like in a DB) and a full drainage system are required. Pressure-moderated (PM) and drained systems build on D systems by adding vents to encourage the moderation of wind pressures across the lamina, thereby reducing the amount of water that penetrates it.
In each of these approaches, all exposed joints should be drained two-stage joints (FS systems are only acceptable with drained joints). Face-sealed EIFS with exposed one-stage joints are not recommended for exterior application over moisture-sensitive substrates. Two-stage joints, in the form of drained sub-sill flashing, are also necessary below windows and at balcony penetrations.
The rain control strategy that should be used generally depends on three primary variables: Exposure–a combination of the climate and the form, size, orientation, and siting of the building; System Quality–a combination of design, materials (including the moisture tolerance of the substrate), workmanship, the confounding effects of weather during installation, and economics; and Performance Expectations–a function of client expectations, minimum code requirements, and so on.
EIFS offer the designer a cladding system with many advantages, but care must be taken to deal with rain penetration issues properly. Face-sealed barrier walls provide a low level of reliability, and should only be used in protected exposures with good design and execution. In many cases a Dual Barrier approach will provide acceptable performance, and drained systems can be used in high exposure applications. Interested readers are encouraged to obtain a copy of CMHC’s EIFS Best Practice Guide for more information and detailed drawings and specifications when it is released later this year.
John Straube teaches in the Department of Civil Engineering and the School of Architecture at the University of Waterloo.
Minimum Recommended EIFS Rain Control Strategies
||FS / DB
||DB / D
the choice of EIFS cladding should be re-evaluated in this situation.
A–two storeys or less, with good overhangs, less than 1500 mm of annual rain fall, and suburban or urban exposure
B–low-rise without overhangs or more than 1500 mm of annual rain, mid-rise suburban or urban exposure. Open or seaside exposure for A
C–high-rise, all exposures. Open or seaside exposure for B
Note: different orientations and heights may have different exposures.
1–full time third party inspection, experienced crew, detailed design and documents (e.g., 3-D isometrics for details)
2–intermittent inspection, average crew, average design and documents
3–little or no inspection, inexperienced or rushed crew, simple design and limited documents
Horizontal Section Through an EIFS at a Two-Stage Joint