Tips for success with exterior insulation and finish systems

November 2, 2015

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All images courtesy Hoffmann Architects

by Arthur L. Sanders, AIA, and Benjamin J. Robinson, AIA
Exterior insulation and finish systems (EIFS) are proprietary wall cladding assemblies that combine rigid insulation board with a water-resistant exterior coating. Popular chiefly for their low cost and high insulating values, they are used on a range of construction types, from hotels to offices to homes.

Unlike traditional stucco, which is composed of inorganic cement-bonded sand and water, EIFS employs organic polymeric finishes reinforced with glass mesh. As an energy-efficient, economical wall covering, EIFS can be effective for both new construction and recladding applications. However, successful use of EIFS is highly dependent on proper design and sound construction practices. Without correct design and detailing, EIFS wall systems have been known to fail dramatically.

Elements of an EIFS wall assembly
EIFS are multi-layer systems that typically consist of six basic components:

Primer may be applied to the substrate before waterproof membrane application, or it may be used on the insulation board before applying the base coat. Although primers are usually optional for EIFS, they may be used to minimize water absorption, reduce efflorescence, improve trowelability and coverage, and promote color consistency.

There are two major types of EIFS. The first, Class PB, represents the majority of EIFS used in North America.

Class PB (polymer-based)
Known as ‘soft-coat’ EIFS, Class PB systems use adhesively fastened expanded polystyrene (EPS) insulation with glass fiber reinforcing mesh embedded in a nominal 1.5 to 3 mm (1⁄16 to 1⁄8 in.) base coat.

Class PM (polymer-modified)
‘Hard-coat’ EIFS were developed for improved impact resistance. Reinforcing mesh is mechanically attached to extruded polystyrene (XPS) insulation, over which a thick, cementitious base coat of 6 to 9.5 mm (1⁄4 to 3⁄8 in.) is applied.

Direct-applied exterior finish system (DEFS)
DEFS is the exterior finish part of EIFS without the insulation. Base and finish coats are applied directly to the substrate. Mainly used for soffits, stairwells, and high-impact-prone areas that do not require insulation, DEFS may be applied to cement board, concrete masonary units (CMUs), exterior-grade plywood, polyisocyanurate (polyiso) board, or other proprietary products.

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Components of an exterior insulation and finish systems (EIFS) include: (1) finish, (2) reinforcing mesh, (3) rigid foam, (4) adhesive, (5) substrate, and (6) steel stud.

EIFS with drainage
Also known as ‘rainscreen EIFS,’ EIFS with drainage are installed over a waterproofing barrier with drainage channels for removal of incidental moisture behind the insulation board. Often, these channels are formed by applying adhesive in longitudinal strips or by using insulation board with vertical grooves. The effect is similar to that of a cavity wall, where the space behind the exterior facing drains or dries any moisture that manages to penetrate the cladding. EIFS with drainage were introduced in 1996, following a 1995 class-action lawsuit involving widespread failure of traditional barrier EIFS.

Although EIFS with drainage address the water-intrusion problems of face-sealed EIFS, they are not a foolproof solution. Should the vapor barrier or moisture retarder fail, water can still enter the assembly. Therefore, air and water barriers must be designed to last the life of the system.

Common EIFS failures and preventions
Originally, EIFS were designed as a ‘perfect barrier’ system—one which provides waterproofing protection at the exterior face of the cladding. The idea of barrier cladding assemblies is to create a face-sealed façade that repels moisture to keep the building dry.

Unfortunately, barrier systems are rarely perfect. All it takes to compromise watertightness is a small breach in the exterior finish, such as cracks from expansion, sealant failure at joints, or impact damage. Once water finds its way into a barrier system, it usually cannot find its way back out. Water trapped in the wall can lead to leaks, wet substrate, mold, deterioration of building components, and eventually, collapse of the weakened cladding.

Any number of deficiencies can lead to EIFS failure. The major culprits are poor workmanship, damp climate, impact damage, building movement, and incompatible or unsound substrate.

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Impact damage that is not repaired promptly provides a pathway for leaks.

Poor workmanship
Sealant joints are a major source of problems with EIFS cladding. Incorrect selection or application of sealant (or sealants missing altogether), provides an easy path for water entry and premature deterioration. Inappropriate sealant may even lead to cohesive failure of the EIFS finish coat. Sealant erroneously applied to the finish coat, rather than to the mesh-reinforced base coat, is a common source of problems.

Missing or incorrectly installed flashings provide a conduit for water infiltration. Door and window openings should incorporate flashings to direct water away from headers and sills. At roof/wall intersections, drip-edge flashings should be installed to channel rain away from the wall face.

Base coat thicknesses that do not meet the manufacturer’s guidelines are another typical source of trouble for EIFS façades. A base coat that is too thin provides insufficient waterproofing protection, whereas a base coat that is too thick may lead to cracking.

Reinforcing mesh that reads through at joint edges or terminations can indicate inadequate coating thickness. Alternatively, the mesh may have been insufficiently embedded in the base coat. Continuing the mesh-reinforced base coat around to the back of the insulation board, known as ‘backwrapping,’ is critical to providing continuous waterproofing protection at edges, penetrations, and terminations. Factory-formed track may be used at foundation terminations instead of backwrapping, when appropriate.

Aesthetic joints (V-grooves) aligning with insulation board joints can lead to cracks as the building moves. Mesh-reinforced base coat should be continuous at recessed features.

Window and door corners, like aesthetic joints, should not align with insulation board joints. ‘Butterfly’ reinforcement, whereby rectangular pieces of reinforcing mesh are laid diagonally at the corners of windows, doorways, and other openings, is important to prevent cracking.

Expansion joints are too often neglected in EIFS construction, but they are no less critical here than with other types of cladding. Expansion joints should be used:

Insulation board should not bridge expansion joints in masonry or concrete substrates. Instead, an expansion joint should be created in the EIFS insulation over the underlying joint.

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Moisture meters may be used as part of an EIFS failure investigation.

Insulation board should meet the manufacturer’s recommended minimum thickness (usually 19 mm [3⁄4 in.]), even at aesthetic joints and recesses. Vertical joints in the insulation should be staggered in a running bond pattern in successive courses, with boards abutted tightly to one another. Gaps between boards should never be filled with base coat or adhesive, which can cause cracking; rather, slivers of insulation may be wedged between boards where needed. Selecting a board adhesive that is compatible with both the insulation and the substrate is critical to successful performance of EIFS.

Climate factors
A humid climate with limited drying potential can devastate some EIFS assemblies, particularly when the rate of wetting exceeds that of drying. Poor design and installation exacerbate this problem by providing avenues for water to penetrate the cladding while the humidity prevents damp walls from drying out.

The amount of rain deposited on a wall depends not only on climate, but also on the architecture and siting of the structure. Building height, overhangs, exposure, and façade details all affect the path of rainfall, channeling more or less moisture toward the cladding.

Cold climates may also lead to premature failure of the system, particularly when EIFS coatings are applied at temperatures below the manufacturer’s design range.

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To true the wall surface, the installer should level the insulation board, rather than build up base coat.

Impact damage
EIFS consists of a thin, brittle coating over a soft substrate and are easily damaged by impact. Holes, dents, or scrapes can lead to water infiltration, so it is prudent to provide extra reinforcement at susceptible locations.

Areas needing impact protection should use heavy-duty mesh, usually 340 to 566 g (12 to 20 oz), rather than standard 127-g (4.5-oz) mesh. For outside corners, the design professional may specify a heavier corner mesh to guard against excess wear and damage. Intricate decorative elements require a lightweight, flexible detail mesh, which conforms to fine contours and ornamental details while still providing some measure of impact protection.

Building movement
Wood substrates tend to exhibit cross-grain shrinking, along with expansion and contraction from changes in humidity. For concrete, movement tends to come in the form of frame shortening, whereby concrete deforms over time due to shrinkage and creep. Steel structures are not immune to the effects of building movement, particularly at long-span beams, where transverse forces are greatest and deflection is more likely. To prevent irregular cracking, sufficient provision for expansion and control joints should be part of the design.

Unsound substrate
Poor quality control in the production of OSB, a common substrate for EIFS, has raised some concerns about premature failure, so a reputable manufacturer with a good track record should be used. Traditional gypsum board, often used with EIFS, tends to exhibit problems with moisture absorption. It should be avoided in damp or humid climates. Even if the substrate is of high quality and suitable for the building location, failure to correctly specify or install substrate attachment may lead to premature cladding problems.

Catastrophic EIFS failure
In 1995, a task force of the American Institute of Architects (AIA) conducted a survey URL of over 200 homes with a dozen different EIFS systems in Wilmington, North Carolina. Of those homes, 68 percent had incorrect or missing sealant joints and 94 percent experienced water intrusion. Earlier that year, homeowners in New Hanover County, North Carolina filed a class action lawsuit[6], against multiple EIFS manufacturers. Under the settlement agreement, an EIFS Inspection Protocol was introduced, which involves moisture detection through resistance probe moisture meters and electronic impedance scanning meters. The testing procedures and criteria established in this protocol have become the standard for EIFS failure investigations.

Design considerations
The performance and longevity of any cladding assembly depends on the proper design and installation of the system, and EIFS is no exception. Sequential coordination of work is one way to avoid defects, particularly at intersections and terminations. The general contractor, framers, window installers, sealant contractor, EIFS installer, and other trades should be organized such that the work of one does not adversely impact the work of another. For large areas, sufficient workforce should be on site to permit application without cold joints or staging lines. Whenever possible, EIFS application should proceed on the shaded side of the building.

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For retrofit projects aiming to improve performance and update appearance, EIFS provide a practical option in terms of aesthetics and function.

Sealant joint and flashing design
The design professional is responsible for determining the appropriate size and location of joints, and for specifying a compatible sealant. In general, low-modulus sealants that maintain their properties when exposed to ultraviolet (UV) radiation are recommended for EIFS. Sealant selection should consider anticipated joint movement, substrate material, cyclical movement, and exposure to temperature extremes. To prevent premature degradation at the bond line, closed-cell backer rod should be used in lieu of open-cell, which tends to retain moisture.

At points where water can enter the wall, (e.g. roof/wall intersections, window and door openings, and through-wall penetrations), it should be directed to the exterior with appropriate flashing. Flashing should be integrated with air seals, sealants, rough opening protection, and other waterproofing materials.

Surface texture anomalies
The phenomenon of ‘critical light’ occurs when natural or artificial light strikes a wall surface at an acute angle, less than 15 degrees, such that tiny surface irregularities cast a shadow. To minimize the negative aesthetic impact of critical light, the EIFS installer should remove planar irregularities, high spots, and shallow areas with a high-quality rasp (file with projecting teeth). Mesh overlaps should be feathered to minimize read-through, and a skim of base coat may be applied to blend laps. To correct critical light defects in existing EIFS, the design professional may specify re-skimming of the original finish coat with an appropriate base coat, followed by application of a new finish after the base coat has dried.

Cool weather application
Damage to EIFS components from low-temperature application may be undetectable in the short term, but tends to emerge later as coatings crack, flake, soften, and delaminate. For most acrylic and cementitious coatings, application is restricted to temperatures of 4 C (40 F) and rising. Below the design minimum, these coatings will not develop proper physical and chemical strength, and they may not coalesce correctly to form a film.

When scheduling EIFS installation, one should avoid the times of year when thermal cycling is at its highest such as autumn, when it is warm during the day and cold at night. Materials with controlled set times will set up more slowly in the cold—the project schedule will need to allow additional time for curing between coats. The ambient temperature and the surface temperature of the substrate—
which may be significantly lower—should be considered. It is advisable to warm certain substrates before application.

Patches and repairs to existing EIFS are particularly susceptible to cold-weather cracking, since seasoned material is combined with new material that has not yet developed its full strength. After initial set, patch areas should be kept warm to assist in curing and to reduce thermal stress.

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Test cuts of existing EIFS cladding can uncover hidden deterioration conditions, which may not be readily apparent from the exterior.

Code compliance
Widespread incidences of failure have prompted code restrictions on the use of EIFS. The architect or engineer should check local building codes to ensure compliance before installation.

Fire rating
In January 2008, the Monte Carlo Hotel in Las Vegas, Nevada caught fire, prompting concerns about flame propagation and EIFS safety. A follow-up investigation found the cladding
in the area of the fire had non-code-compliant lamina that was significantly thinner than required, as well as large decorative elements exceeding maximum allowable EPS thickness. Manufacturers test EIFS systems for fire resistance; however, substituting untested coatings, insulation, or substrates for approved EIFS materials have been shown to increase flammability. The system installed should be identical to the one that has been fire-tested and approved.

Energy code
Mounting energy concerns have driven the International Energy Conservation Code (IECC) and other relevant codes, such as American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, to ever more stringent requirements. Since 2006, the IECC has required both stud cavity insulation and continuous exterior insulation. Continuous insulation is integral to EIFS and retrofitting an existing building with EIFS can be a simple and inexpensive way to comply with increasingly rigorous energy codes.

Wind load
Compared with mechanical attachment, adhesive attachment of EIFS board insulation has been demonstrated to provide superior wind load resistance. To achieve full design performance, the supporting construction must be free from damage, defects, and contamination before insulation is adhered. Sheathing must be capable of independently resisting anticipated wind loads.

Building codes
The 2009 edition of the International Building Code (IBC) was the first to include a section on EIFS and the guidelines, which remain unchanged in the 2012 edition of the model code, and incorporate information on both traditional EIFS and EIFS with drainage. However, the section is brief and directs users to refer to manufacturers’ guidelines.

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At the corners of windows, doors, and louvers, EIFS should incorporate butterfly reinforcement, with diagonal pieces of mesh that reinforce and prevent cracking.

Field verification and quality control
With construction underway, the design professional should verify the proper materials have been ordered and delivered, and that materials have been shipped and stored at appropriate temperatures and conditions. Before EIFS application, the architect or engineer should check the substrate for correct surface preparation, cleanliness, and proper tolerances. To confirm construction complies with drawings, specifications, and manufacturer’s recommendations, the design professional may conduct periodic field evaluations of the EIFS installation progress. He or she should confirm the correct installation of critical related elements, including flashing, sealant, windows, and doors.

EIFS are proprietary systems. Each manufacturer conducts its own research and development for compatibility and performance of their independent EIFS product. Therefore, it is important to specify an entire system from a single-source manufacturer to avoid compatibility issues. Part of the field verification process should include confirmation that the entire assembly functions as one integral system. Many manufactures and industry organizations provide online inspection manuals and verification checklists that can be used to guide independent quality control evaluations.

Maintenance and repair
To keep EIFS looking and performing their best, building owners should implement inspection and maintenance practices to address incipient problems promptly.

EIFS finishes and sealants should be inspected for damage or wear at least twice a year. EIFS should be cleaned thoroughly every five years—locations prone to algae and fungal growth may require more frequent cleaning. Options for EIFS cleaning include commercial detergent, pressure washing, or a trisodium phosphate (TSP) solution. Washing with cold water is recommended, as hot water can cause acrylic finishes to soften. Difficult stains—such as those from wood, tar, asphalt, efflorescence, graffiti, or rust—may require sealing and re-coating.

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Failure to account for the behavior of dissimilar materials can lead to failure of both the EIFS and the adjacent cladding assemblies.

Elastomeric coatings can provide a fresh appearance and added waterproofing protection for worn EIFS surfaces. However, such coatings may alter the texture, sheen, and vapor permeability of the original cladding. Existing sand finish with a small aggregate size may lose its texture after recoating. One should avoid dark-colored coatings, which absorb heat and tend to crack. To verify compatibility of an elastomeric coating with the existing EIFS finish coat, most manufacturers recommend testing as per ASTM D3359, Standard Test Methods for Measuring Adhesion by Tape Test. Typically, EIFS manufacturers produce their own elastomeric coatings, which are designed to be compatible with their cladding systems.

To address EIFS damage or persistent stains, resurfacing may be necessary. First, the installer should clean and dry the area, then trowel a skim base coat to fill voids in the surface. Once the base coat dries, a new finish coat should be applied, per the manufacturer’s instructions. When color-matching a new finish with an old one, a physical sample should be employed, as age and exposure may have affected the original color. Differing application technique may prevent refinished areas from blending completely with the existing finish, so resurfacing an entire panel to a termination usually produces better results than a smaller patch.

Flashing and sealant repair
Common points of water entry, including window and door perimeters, expansion joints, intersections with dissimilar materials and roofs, penetrations, and terminations should be periodically checked. Removing worn sealant may damage the existing EIFS, which must then be repaired and allowed to dry before new sealant may be installed. The design professional should confirm the new sealant is compatible with the surface of application.

EIFS damage repair
Depending on the depth and severity of EIFS damage, repair may entail removal and replacement of finish, base coat, reinforcing mesh, and even insulation board. Prolonged and pervasive water infiltration may also require replacement of substrate materials and possibly of the entire wall, including structural support members. For puncture or impact damage, such as dents or holes, the manufacturer should be consulted for instructions, particularly if the system is still under warranty. Shopping plazas, for instance, are vulnerable to damage from store signs that have been removed without repairing fastener holes. One should check with the manufacturer to determine whether such punctures void the warranty.

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Signs, lights, and other fixtures that are removed from EIFS leave fastener holes that admit moisture and lead to deterioration.

EIFS performance
If correctly designed, installed, and maintained, EIFS provide durable envelope protection. The oldest systems in the United States were installed in the late 1960s, and some are still in service. For those concerned about the long-term viability of EIFS in light of the series of cladding failures in the 1990s, a 2006 study from the Oak Ridge National Laboratory[12] (ORNL) should put many of those apprehensions to rest.

Over a 15-month period, ORNL tested a number of cladding types, including brick, stucco, concrete masonary unit (CMU), cementitious fiber board, and EIFS, in the challenging mixed-coastal climate of Charleston, South Carolina. Of those wall systems tested, the best-performing was an EIFS assembly including a liquid-applied water-resistive barrier coating and 100 mm (4 in.) of EPS insulation board. The study validated vertical ribbons of adhesive provided an effective means of drainage within an EIFS wall assembly.

The ORNL study demonstrates that the new generation of EIFS successfully rectifies problems inherent to earlier systems. When designed with attention to moisture management, modern EIFS can be a reliable, cost-effective option for an energy-efficient building envelope.

 Origins of EIFS in America

After the ravages of World War II destroyed vast swathes of Europe, cities looked to rebuild quickly and inexpensively. Thus EIFS were first introduced in Europe as a wall system that enabled the rapid redevelopment of devastated areas. Later, in 1969, EIFS were introduced to the United States, gaining popularity during the energy crisis of the 1970s, when retrofitting walls with exterior insulation improved performance and cut energy costs.

The EIFS industry continued to enjoy steady growth through the 1980s, thanks to its insulating properties, light weight, aesthetic flexibility, low cost, and versatility. In addition to new construction, EIFS were commonly used for retrofits, where it could be applied easily over existing exterior walls to improve the energy profile and provide a fresh appearance. Available in a wide range of colors, shapes, and textures, EIFS allowed architects the flexibility to design new façade profiles at a relatively low construction cost.

This versatility led to the proliferation of EIFS in the residential and light commercial markets. In 1981, the EIFS Industry Members Association (EIMA) was formed to advocate for EIFS manufacturers and improve product performance.   

 EIFS and Green Building
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By providing continuous thermal insulation (ci), EIFS can serve as an energy-efficient wall cladding option.

As new building codes require more stringent energy standards, there has been greater demand for improved thermal regulation and moisture control at the building envelope. One of the main benefits of exterior insulation and finish systems (EIFS) cladding is their strong environmental performance with low initial cost. By moving insulation outside the wall cavity, EIFS brings the dewpoint to the exterior of the sheathing, minimizing condensation within the wall, that can lead to heat loss. Adhesively fastened EIFS further reduce the incidence of moisture intrusion, in that it does not puncture air barriers with cladding fasteners. Thermal bridging, the process through which heat is transferred across thermally conductive elements of the wall assembly, can be reduced, or even eliminated, through the use of continuous exterior insulation (ci).

For retrofit projects aiming to improve performance and update the building appearance, EIFS can be a practical option. Lightweight and easy to install, EIFS are often selected for recladding of existing buildings, where it provides a quick, low-cost façade makeovers that can also cut energy costs.

EIFS projects aiming for Leadership in Energy and Environmental Design (LEED) certification can earn credits for reduced energy consumption. By providing a highly insulated building envelope, EIFS permit the downsizing of heating and cooling equipment, resulting in a net energy savings.

On the downside, EIFS are not going to earn many points for materials and resources. At present, none of the commonly used systems incorporate recycled or otherwise sustainable content, and the lifespan of EIFS may be shorter than other cladding materials. So, while EIFS can improve building envelope performance at a low initial cost, owners should consider that EIFS façades may eventually need to be replaced.

Arthur L. Sanders, AIA, is senior vice president and director of architecture with Hoffmann Architects Inc., an architecture and engineering firm specializing in the rehabilitation of building exteriors, with offices in Connecticut, New York, and Washington DC. As manager of the firm’s Connecticut office, Sanders lends his extensive experience in architectural remediation to organizing technical resources efficiently, overseeing project completion, and mentoring junior staff members. A strong proponent of specifications in design, he has been active in CSI for over 30 years and is secretary of the Board of Directors for the Connecticut chapter of the American Institute of Architects (AIA). He can be reached via email at[14].

Benjamin J. Robinson, AIA, is project architect with Hoffmann Architects in Connecticut. With 15 years of experience resolving failure in a range of building types and climates, Robinson develops rehabilitation solutions for leaks and other signs of distress in EIFS cladding. As chairperson of the Hoffmann Architects Training and Resources Committee, Robinson leads the firm’s professional development program and oversees implementation of company technical standards. He is an active member of both the CSI and the AIA. He can be reached via email at[15].

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