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Advertising supplement provided by Sto Corp.

EIFS—The Next Generation

Class PB EIFS have been the predominant type of EIFS sold in North America, mainly because they combine low installed cost in an attractive multi-functional exterior wall covering. In recent years, as a result of building code requirements, several types of EIFS have been developed that incorporate traditional moisture protection, asphalt saturated felt, behind the EIFS. In most cases these newer types of EIFS require mechanical attachment, because EIFS adhesives will not stick to sheet goods. Mechanical fasteners have drawbacks. They act as thermal short circuits, which cause heat loss and can cause ghosting or telegraphing of the fasteners through the finished wall surface. They may also limit wind load resistance of the assembly. More recently, EIFS—the next generation, was developed to overcome the limitations of traditional moisture protection and mechanical fasteners. EIFS—the next generation incorporates a fluid applied membrane behind the EIFS wall covering on the substrate (Figure 3). The membrane has two functions:

• Air infiltration and exfiltration resistance
• Secondary moisture protection

As an air barrier the fluid applied membrane minimizes the risk of condensation within the building envelope by eliminating mass transfer of warm moisture laden interior air (in cold climates) to the exterior. As a secondary moisture barrier it provides a second line of defense in the event of a breach in the EIFS caused by impact damage or abuse. In combination with vertical ribbons of adhesive and starter tack with weepholes, the assembly provides both primary and secondary moisture protection and a means for incidental moisture to weep to the exterior. Unlike traditional moisture protection prescribed in the code (asphalt saturated felt) or housewraps, the fluid applied membrane is structural once it is applied to the substrate, since it essentially coats and adheres to the substrate. This eliminates the pitfalls associated with felt or fabric moisture protection—punctures, and the potential for tearing and mis-lapping during installation. It also optimizes performance as an air and moisture barrier. Since the membrane is seamless and bonded to the substrate it won’t leak water through holes or tears, and it won’t flutter and compromise air barrier performance in the presence of air pressure differences or fluctuations, as do sheet goods3. The membrane is fully compatible with EIFS adhesives, and thus eliminates any need for mechanical attachment of insulation board, normally required over sheet goods. Thus thermal bridging is eliminated and negative wind load resistance, often limited by pull through of the EPS insulation board through the fasteners in mechanically attached systems, is no longer a limiting factor.

Figure 3. EIFS--the next generation incorporates a fluid applied membrane that functions as an air barrier and secondary moisture barrier in the wall assembly. Weepholes (not shown) behind the drip edge of the starter track direct water to the exterior in the event of a breach in the EIFS wall covering caused by impact or abuse.

Performance criteria for EIFS — the next generation have been established by model code agencies. In particular stringent criteria for fluid applied membranes are established by SBCCI4 and ICBO5. The SBCCI criteria require the membrane to sustain a static head of 21.6 inches (55 cm) of water for a period of at least 5 hours before and after aging. They also require resistance to air infiltration not to exceed 0.06 cfm/ft2 (0.305 L/s•m2) at a pressure differential across the wall section of 0.3 inches (7.6 mm) of water. ICBO acceptance criteria require no water leakage after exposure to cyclic wind loading followed by 75 minutes of water spray with simultaneous air-pressure differential that approximates a sustained 50 mph (80 km/h) wind. In essence, these performance criteria require the wall to be waterproof and resistant to air infiltration before the EIFS wall covering is put in place. They also require the membrane to be resistant to the affects of UV aging even though it will not be subjected to UV exposure while in service. This substantially exceeds the performance requirements for conventional water-resistive barriers prescribed in the code. Refer to Table 1 for a complete listing of performance criteria for EIFS—the next generation.