EIFS, One-Coat and 3-Coat Stucco Assemblies
by Osvaldo Joya, Director, Pre-construction, LJP Construction Services
Due to higher energy standards required in each building code cycle, the use of exterior insulation has grown and will continue to grow as an important strategy to meet Title 24 requirements. As Net-Zero construction mandates approach in the State of California, home builders are struggling with cost effective solutions for compliance. Relying on HVAC systems and thicker structural walls are unlikely to be economically feasible approaches for new construction.
There are several One-Coat systems on the market, and most of them have been verified by ES-ICC code reports and ASTM standards and are compliant plaster systems. They consist of a 3/8” inch minimum layer of base coat (cement plaster mixture) embedded in metal or fabric lath. The use of continuous insulation is not presently required. However, when exterior rigid insulation is used the energy efficiency of the exterior walls can substantially increase.
For a system to be considered an EIFS (Exterior Insulation Finish System), it must meet certain requirements per AWCI (Association of the Wall and Ceiling Industry). This is the association tasked with certifying EIFS Inspectors for city special inspection mandates during construction. A typical requirement is that EIFS must always have insulation boards. The minimum thickness of the boards must be ¾-inch. The base coat must use a reinforcing membrane, typically not a metal lath, but rather a fabric reinforcement. The lamina (top layers) consist of a base and top/finish coat. The base coat may be cement based, but can also be an adhesive. The top coat can be one of several materials, but typically it will be a mixture of acrylics and elastomeric finishes. One-Coat systems will almost always be cement plasters (stucco) applied directly to lath.
A few years ago, EIFS systems had significant failure rates on major projects. The EIFS that were used more than a decade ago were “Direct Applied” or “Barrier” systems. However, in the market today, EIFS manufacturers do not use Barrier systems for exterior exposed conditions. EIFS used as an exterior cladding are always specified as “Drainable” EIFS. This requirement increased the water resistiveness of the assembly by creating a continuous drainage plane behind the insulation boards. This is also true of modern One-Coat systems (if specified correctly). Unlike Barrier systems that relied on the surface plane to prevent all moisture from penetrating the wall, current systems have a primary water barrier over the sheathing to protect from incidental moisture intrusion. EIFS assemblies typically rely on fluid applied systems. One-Coat systems will have the option of having either fluid or sheet membranes.
Both systems, EIFS and One-Coat, when compared with traditional 3-Coat stucco assemblies, can provide a higher water resistive capacity due to the designed drainage plane. 3-Coat stucco systems traditionally rely on having a drainage plane created when the stucco cures and “wrinkles” the building paper to create drainage channels, however this is not always the case and cannot be verified in field installation. That said, new code requirements are now pushing for a designed drainage plane for 3-Coat stucco as well, because of its proven effectiveness for draining walls faster. Unlike 3-coat stucco, the one-coat and EIFS is a premeasured bagged synthetic material. This product is much more resistant to shrinkage cracking and the appearance is typically a higher quality. Additionally, the product is typically painted and thus has less of the “staining” that is commonly seen on 3-coat.
Both EIFS and One-Coat systems, if specified and constructed correctly, do not pose a higher risk when compared to traditional 3-Coat stucco. Building science for energy performance and moisture control has long argued for exterior insulation as an effective approach for exterior wall construction. Exterior rigid insulation can outperform interior insulation systems, which are inherently limited to the depth of stud bay cavities and still create thermal bridging through stud wall connections to the exterior structural panels. As our friend and colleague, Dr. Joe Lstiburek, has eloquently stated, “When you are cold, you put on a sweater, you don’t eat it.”
LJP Construction Services
For 25 years, Irvine, CA-headquartered LJP Construction Services has been at the forefront of the quality assurance movement on behalf of builder and insurance clients, raising the bar and pushing the limits of quality control. With employees coast to coast, LJP has tracked construction inspection data nationally over the past several years with its new and unique CaptureQA® app monitoring of all building types– SFDs, MFAs, THs, mid-rises, high-rises, resorts, hospitality and others. More importantly, LJP’s builder and insurance clients now have another advanced and powerful tool in their arsenal of QA/QC solutions, generating state-of-the-art business intelligence to help manage more effectively and wisely through the current trade contractor labor shortage.