By Michael DeLaura, LEED AP, and John Edgar
In an effort to build more energy-efficient and sustainable buildings, there has been a shift toward energy-efficient lightweight cladding options for the exterior. One such product is exterior insulation and finish systems (EIFS).
These assemblies provide numerous features and benefits including an air barrier, continuous insulation (ci), and a decorative finish. Tracing their roots back to early 1950s Germany, the product was originally designed for commercial use, making its way to the European residential market a decade later and, subsequently, Canada and the United States.
The traditional system consisted of an adhesive applied using a notched trowel to form vertical ribbons of adhesive to attach the expanded polystyrene (EPS) insulation board to the substrate. The EPS was rasped or sanded before application of the basecoat, and a fibreglass mesh was embedded into the wet base coat. The final layer consisted of the finish, available in a sand, swirl, or freeform texture in various colours. EIFS became a popular cladding since features such as curves, quoins, arches, reveals, and accents were easy and economical to fabricate and install. It offered a new look and an energy-efficient way to wrap the outside of the building providing continuous insulation and lowering heating and cooling costs.
In the mid-1990s, driven by air-barrier code requirements, a waterproof air barrier element was added to EIFS, providing airtight construction and a waterproof redundancy behind the EIFS. Since that time, Canadian Construction Materials Centre (CCMC) developed a robust technical guide for EIFS evaluation to prove the durability of the systems in Canadian climatic conditions. No other cladding is evaluated under such extreme testing. The CCMC guide has since evolved into Underwriters Laboratories of Canada (ULC) S716, Standard for Exterior Insulation and Finish Systems, which is now scheduled to be introduced into the model 2015 National Building Code of Canada (NBC).
EPS insulation can be installed at up to 140 mm (5 ½ in.) thick to achieve significantly higher R-values than other claddings, provided proper fire tests have been done. Placing the insulation outbound of the sheathing eliminates thermal bridging, which is the path of low thermal resistance (e.g. afforded by mechanical anchors, shelf angles, steel studs and the like) that allows thermal energy to pass. In some cases, thermal bridging woes can reduce the effective R-value of the steel stud cavity insulation by nearly half.
The recent introduction of the National Energy Code for Canada for Buildings (NECB) heavily favoured use of continuous insulation (ci) outbound of the structure in order to meet its performance requirements, making EIFS an attractive solution.
EIFS assemblies evolve with air/moisture barriers
The recent publication of the report, “Building Envelope Thermal Bridging Guide-Analysis, Applications and Insights,” which was developed by Morrison Hershfield and published by BC Hydro shows the real effect of thermal bridging in a wall envelope. EIFS has shown to be one of the best and most economical solutions to thermal bridging.
Over the last 15 years, one of the biggest changes in the EIFS assembly has been the introduction of a fluid-applied air/moisture barrier installed over the substrate. This offers the option to use one continuous barrier over the substrate regardless of the cladding. The fluid-applied air/moisture barrier is seamless, and provides protection against moisture intrusion, water leakage, mould, and mildew.
EIFS offers design flexibility in that the structure can be waterproofed with various claddings. One advantage of a fluid-applied waterproof air barrier is the building can be protected from inclement weather once the windows and doors are installed. Air barriers also lower heating and cooling cost and increase occupant comfort. They help maintain constant temperature by controlling air leaks through the wall assembly, which can contribute to heating and cooling loss.
The National Institute of Standards and Technology (NIST) study, “Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use,” confirmed air barriers promote energy savings from 30 to 40 per cent for heating climates. An air barrier can be vapour-permeable or impermeable, depending on the climate and location.
As Canada is a mostly heating climate, vapour drive tends to be from inside to outside. This means the vapour barrier will go on the warm side—the inside. If the insulation strategy is to have some insulation in the wall cavity and some on the exterior, then a vapour-permeable air barrier may be appropriate. If all the insulation is outbound, then the sheathing becomes the warm side and a vapour barrier material would be appropriate.
Contractors started building a more efficient process with EIFS panels since they are manufactured in an enclosed shop or warehouse. Benefits include:
- increased quality control (i.e. all components are installed at ground level without the limitations of working at elevations; further, humidity, temperature of materials, and mixing is controlled);
- highly engineered panels and connections;
- no interruption during inclement weather;
- improved productivity;
- little or no scaffolding required; and
- reduced safety risk in comparison to stick-built construction.
One of the major advantages of panelization is construction schedule compression since the panels can be manufactured offsite and installed as soon as the project site is ready, significantly reducing the schedule’s timelines. Since the units are manufactured offsite, the wall panels are built while the floors are being poured. Once the floors are completed, the panels are installed using a tower crane onsite.
Panels are either structural or non-structural. In the former category, the panel assembly consists of the following components:
- metal stud frame;
- exterior sheathing;
- air barrier;
- mesh; and
The panels are delivered to the site on a flatbed trailer and attached to the substrate with a clip or anchor placed in the concrete when it is poured. The panel is welded or bolted to the clip. A double silicone sealant joint installed between panels maintains air barrier continuity with a rain-shedding outer protection.
The non-structural panel assembly consists of:
- EPS insulation;
- optional air barrier;
- mesh; and
The EPS insulation has a furring channel embedded in the foam with a sleeve on each end to allow for a mechanical attachment to the substrate. The panel is attached to the substrate with a mechanical and adhesive attachment. The lightweight panel type is installed on virtually any type of project with no need to modify an existing structure for retrofits and remodels. This panel uses a ship-lap design as one method for joining the panels. A silicone sealant joint installed between the panels provides a watertight exterior cladding assembly. The non-structural panels are ideally suited for existing low-rise buildings where disruption of the existing business must be avoided.
The decision to use panels should begin early in the stages of design development. The design professional must determine whether the project is suited for prefabrication. However, not all areas of the project need to be panelized—there may be areas where there is an in-place application depending on tie-ins and connections.
A new development in the EIFS industry was the introduction of finishes with self-cleaning properties. Super-hydrophobic properties results in the finish being rinsed clean with each rainfall. A clean finish provides high resistance to mould, mildew, and algae, reducing maintenance costs. This finish is available in various colours and textures. A smooth coating is offered to apply over existing EIFS surfaces and other exterior substrates.
EIFS offer specialty finishes that can replicate brick, granite, limestone, metal panels, and precast. These finishes are easier to install and require fewer specialty trades than the traditional cladding material. Specialty finishes offer a cost-effective aesthetic option, as well as increase energy efficiency and moisture protection. The finishes offer an identical look to the natural cladding but are more lightweight, allowing the owner to build a lighter building with an air barrier; continuous insulation, and a decorative finish.
Since EIFS only requires deflection criteria of L/240, in comparison with other claddings such as brick and limestone at L/600, an owner can save on the structural steel’s cost since the structure is built to lower deflection criteria.
Deflection criteria is the extent to which a material can bend or flex during its lifetime. A cladding with a deflection of L/240 is more flexible than a cladding with a deflection of L/360, L/480, or L/600. Claddings with a higher deflection criteria require a heavier structure to support the less flexible cladding’s weight.
EIFS with a metallic finish—designed to replicate metal panels—offers an expedient and cost-effective solution to metal panels since the material can be installed onsite and adjusted to allow for any changes in framing. Unlike traditional metal panels, EIFS with a metallic finish has continuous insulation and there are no penetrations through the cladding for attachment to the substrate.
EIFS testing and research
Independent testing of EIFS has been conducted to demonstrate its long-term performance compared to other claddings. In 2003, the U.S. Department of Energy (DOE) contacted EIFS Industry Members Association (EIMA) and proposed a thorough hygrothermal evaluation of EIFS alongside numerous other commonly used claddings.
The association worked with the Oak Ridge National Laboratory (ORNL) to design and construct a specific facility dedicated to this purpose. Testing was performed in two phases, from January 2005 to May 2006 and June 2006 through June 2007.
The ORNL testing demonstrated EIFS with a liquid-applied water-resistive barrier (WRB) performed better in that climate than any assembly—15 individual wall sections that included barrier EIFS, EIFS with drainage, stucco, brick, and siding were also tested. Further, the EIFS assemblies had superior drainage capability compared with the other claddings as evidenced by the lower relative humidity (RH) values through the various wall components.
The best overall performance was an EIFS with 101.6 mm (4 in.) of ci applied over a liquid-applied WRB with an empty (no batt insulation) stud cavity. Computer modelling was validated against field data to show actual long-term wall assembly performance could be calculated for any climate zone.
Over the last 50 years, exterior insulation and finish systems have demonstrated they are versatile, lightweight, energy-efficient claddings installed over various substrates. Independent third-party testing has shown EIFS out performs other types of exterior cladding. Whether field-applied or a pre-fabricated panel, such assemblies can be considered for existing, new, or retrofit projects.
Michael DeLaura, LEED AP, has been with Sto Corp. as an exterior cladding specialist since 1996. A 28-year veteran of the EIFS and coatings industry, he is an active member of the U.S. Green Building Council (USGBC), specifically the Middle Tennessee and Hampton Roads chapters. DeLaura can be reached email@example.com.
John Edgar is technical director for Sto Canada. He has been with the company for more than 20 years, serving in multiple leadership positions involving both Canadian and U.S. technical matters. Edgar has held positions including past-president and current chair of the EIFS Council of Canada, former member of the Standing Committee on Environmental Separation (part 5) of the National Building Code of Canada (NBC), and chair of Underwriters Laboratories of Canada (ULC) S716 Task Group for EIFS. He can be reached at firstname.lastname@example.org.