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Stucco
Synthetic Stucco Failures
Tony Tufariello, Stamford
First, mass failures of fire retardant plywood roof sheathing led to nearly $2 billion in losses during the late-1980s and early 1990s. Then, the use of polyisobutylene (PIB) plastic pipe for residential construction led to chronic leaks and a settlement offer of $850 million. Now, exterior insulation and finish systems (EIFS), sometimes called synthetic stucco, are experiencing a number of failures in specific areas of the U.S., generating class-action lawsuits. This article will describe this relatively new material, the causes of its failures, and the linkage to installation practices.
Introduction
Conventional stucco exterior wall finishing has been in use around the world for hundreds of years. Stucco is a labor-intensive portland cement, sand, and lime product usually applied in three coats over metal mesh reinforcement, requiring 2 to 7 days of curing between the initial “scratch coat” and the second “brown coat.” That is followed by 9 days of curing before the thin finish coat is applied - certainly a time-intensive process. In common with most other cement-based products, it is relatively moisture permeable, allowing any water that infiltrates between it and the wall sheathing to slowly migrate outward.
The high labor costs, time-intensive application requirements, and geographic scarcity of some construction trades, have decreased the market for traditional stucco and led to the search for faster applied lookalikes. The desire for a stucco-like finish combined with the need for higher wall insulation ratings spurred development of synthetic stuccos, more formally known as “exterior insulation and finish systems” (EIFS).
Originally developed in Europe for use on concrete and masonry walls and in use stateside for nearly 25 years, these EIFS products first require attachment of an expanded polystyrene insulating board to the exterior wall surface, using adhesives, or occasionally, mechanical fasteners. A base coat of synthetic material is then troweled on, and a layer of fiberglass mesh reinforcement is then embedded onto the outside surface of the foam board. Once dried, one or more finish coats of acrylic-based synthetic stucco are applied to provide a water tight surface. In fact, unlike traditional cement-based stucco, the EIFS types are impermeable to water vapor - the source of at least some of the current problems.
Hardly a construction rarity, an estimated 260 million square feet of the product was applied in 1995 and problems have been reported from both high humidity areas like the Southeast and drier areas like Austin, Texas.
Exposed Businesses
Several business classes are potentially exposed to negligence lawsuits involving the failures of EIFS materials on both residential and commercial structures, including:
¨ Manufacturers of EIFS systems, who will invariably be defendants in cases alleging premature failure and consequential water damage.
¨ Installation contractors, whose workmanship, flashing, or caulking practices may have contributed to water intrusion and synthetic stucco failures.
¨ Building supply dealers, who could be called upon to contribute to settlements if they promoted the systems, took cooperative advertising money from the manufacturers, or recommended installers.
The EIFS Products vs. Cement Stuccos
The major differences between traditional and synthetic stuccos include the following:
¨ Cement stuccos are more “mature” products, in use for hundreds of years and having a base of experienced installers.
¨ Cement provides a high compressive strength in the finished coating, good surface hardness (impact resistance), and low coefficients of thermal expansion.
¨ Cement provides relatively high moisture permeability, which allows any minor water intrusions through cracks to slowly diffuse outward through the exterior surface.
¨ Traditional stuccos have high installation costs but relatively low material costs.
On the other hand, EIFS products - consisting of one or two coats of an acrylic topcoat over a one coat synthetic binder - are applied over foam boardstock, and provide some advantages over cement stucco:
¨ Lower final rigidity than cement, allowing more structural movement without surface cracking. This property permits installation more quickly after framing and sheathing, because the material can better withstand the normal shrinkage of wood framing induced by drying.
¨ Much higher thermal insulation values, due to the underlying foam boardstock. The system applies this insulation where it is most effective - toward the outside of exterior walls.
On the negative side, some EIFS products can be too moisture impermeable, preventing the drying of internal wall cavities wet by small water leaks. The synthetic materials can also be expected to have less uniform and higher thermal expansion, since several different materials make up the finished “sandwich.” EIFS materials have much lower surface hardness and can be more easily dented by ladders or thrown objects.
The Field Experience
In the normal aging of any structure, settling, the shrinkage of framing as it dries, and deteriorating caulk joints and weather seals can be expected to allow small quantities of rain and melted snow to enter the structure between the exterior wall surface and the wall sheathing beneath it. Traditional cement stucco does crack and allow water intrusion of this type, but its relatively high permeability to moisture usually allows quick drying of the interior surfaces with no further damage.
Many EIFS stuccos, on the other hand, do not allow such drying, being nearly moisture tight. This has led to rotting of structural supports and sheathing and damage to interior finishes. Because of such experience, around a dozen class-action lawsuits have been filed by homeowners against EIFS manufacturers and the installing contractors. In the Wilmington, North Carolina area alone, which has been an area reporting many problems with the material, it is said that 2,000 homes have suffered failures of the exterior finish.
In fact, in a group of randomly tested homes with EIFS wall finishes, fully 95% were found to have some moisture problems, with the resulting damage estimated to average $3,000 to $5,000. Similarly, a study of such homes by the American Institute of Architects found “unacceptably high” moisture levels in 90% of the 205 EIFS homes it tested. While the problem is not yet of massive size, some
homebuilders in South Carolina have reported damages of $30,000 to $100,000 in some homes and insurers have reported “total losses” in homes only five years old.
Reacting to these loss trends, one major insurer of contractors has announced its intention to decline to provide liability coverages to any insureds that use these EIFS materials on residential construction. Indeed, most of the problems reported with EIFS have involved residential structures, but high winds have reportedly stripped the systems from the walls of larger commercial buildings. Water intrusion is thought to be a contributing factor in commercial structures as well, because the low moisture permeability of many EIFS types leads to conditions which expedite the rotting of wood supports or even the corrosion of steel fasteners.
Although problems with EIFS materials have been reported from around the U.S., the Carolinas appear to have the greatest concentration of failures due to the surge of residential development, the typical relaxation of workmanship standards as a consequence, and the high ambient humidity which makes the drying of wall cavities a very slow process. It should also be noted that an estimated 25,000 homes are built in Florida each year using these products.
Possible Controls
Despite some localized and expensive water intrusion problems with barrier-type EIFS, builders like the design flexibility of the product, cost advantages, and high thermal efficiency, so modifications will no doubt be developed to solve the apparent problems. Some of the design or installation changes that may help stem further losses of the type seen are:
¨ The incorporation of “mesh weep” or drainage systems to allow the escape of water trapped behind the wall surface.
¨ The use of “rain screen” or “pressure equalization” venting technologies, to vastly reduce water infiltration tendencies of EIF systems by equalizing the pressures on the outer and inner sides of the synthetic stucco.
¨ The avoidance of do-it-yourself markets, where expertise will be lacking, combined with provisions by manufacturers for contractor training and certification. Such certification standards are now in development.
¨ Specific manufacturer advice on the types of effective flashing to be used around the doors and windows available to the residential market.
¨ Preference by the manufacturer for the installation of both flashing and caulking by the EIFS contractor, to assure compatibility of such materials with the synthetic stucco.
¨ The conformance of EIFS manufacturers and installers to engineering standards for the products currently being developed by the EIFS Industry Members Association (EIMA) and the American Society for Testing and Materials (ASTM).
In North Carolina, where most EIFS damage claims have occurred, the building code was revised on March 12, 1996 to require a “mesh weep” system behind EIFS walls in order to provide an exit path for trapped water.
The makers of EIF systems stress that water infiltration around windows and doors is the primary culprit in the failures seen, but builders and building inspectors point out that reliance on caulking for water tightness is a self-defeating prospect, because all such sealants eventually fail and none are perfectly applied initially. Others note that the synthetic stucco makers provide window flashing details more pertinent to commercial windows than to residential units - a failing that must be addressed.
Conclusion
The types of synthetic stucco with installed drainage systems may greatly reduce the failure incidence of the EIFS materials, but their field experience on residences is limited. For the hundreds of thousands of homes constructed using the older barrier forms of the product, some local real estate commissions have declared that the presence of a synthetic stucco exterior is a “material fact” which must be disclosed to potential buyers. The likely negative effect of such disclosures on sales may encourage additional litigation against manufacturers and installers as will the continuing failures in homes already constructed. Given the extended periods over which deterioration of coatings or structures occur, losses involving this material may allow the “stacking” of insurance limits where occurrence-basis policies were issued.
Underwriters evaluating the products liability exposures of EIFS manufacturers or the completed operations for installation contractors must consider both the large latent pool of older design (barrier) synthetic stucco applications and the relative lack of experience for the newer drainage system designs in the residential market.
As with most problems of an engineering nature, solutions will either be found or other competitive products will be developed. Given the widespread builder acceptance of the EIFS products, it is likely that they will be modified to overcome present limitations, hopefully before their field experience deteriorates to the extent of some other construction-related materials.
Legal Disclaimer
This article describes historical or potential exposures and pertinent safety or loss controls of which we are now aware, as well as relevant examples of case law, statutes, and regulations. Not all exposures, losses, or loss controls are reported and others may be relevant in particular circumstances. This material may need revision from time to time, but we do not undertake to do so. We encourage you to consult with appropriate professionals including legal counsel and to obtain the original texts of materials referenced with respect to the matters discussed herein. |
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