EIFS tops the charts

Exterior Insulation Finish Systems (EIFS) performed better than brick, stucco and fiber cement siding in US Department of Energy (DOE) tests measuring energy efficiency, moisture intrusion and temperature control.

Based on the study, EIFS (including EIFS with drainage) is an outstanding exterior cladding choice for achieving the key building performance goals of energy efficiency, temperature control and moisture control in mixed, coastal Zone 3 climates. The study further states that EIFS does not absorb moisture or retain heat as does brick and stucco. In addition, EIFS controls heat flow more efficiently.

The DOE, through the Office of Energy Efficiency and Renewable Energy's Building Technologies Program, and the EIFS Industry Members Association (EIMA), sponsored the study conducted by researchers at the Oak Ridge National Laboratory (ORNL).

"Up to now, there has been a lack of understanding of the hygrothermal (i.e., temperature and moisture control) performance of all types of wall systems due to a lack of real world data measuring how wall systems perform as a whole," says Stephan E. Klamke, EIMA executive director. "One of the strengths of this study is that it considers the entire building envelope over an extended period of time."

The ORNL testing was done on a building constructed near Charleston, S.C., that features exterior wall panels made from various claddings and assemblies. Each panel is fitted with a sensor array that provides a full profile of temperature, heat flux, relativity humidity and moisture content values. The data was collected 24-hours-a-day and transmitted back to the ORNL research facility located in Oak Ridge, Tenn., where the data was extensively analyzed.

Key findings of the study gathered by ORNL researchers between January 2005 and June 2007 include:

* In Phase II, one of the best performing wall system configurations was comprised of EIFS that included a liquid applied water-resistive barrier coating and four inches of expanded polystyrene insulation board. All of the thermal insulation was placed outbound of the sheathing (no stud cavity insulation). This EIFS wall configuration performed better than brick. Brick had the lowest thermal and moisture performance among the claddings and wall configurations studied, followed by stucco (both 3-coat and 1-coat).

* EIFS absorb little moisture and maintain a consistent, acceptable moisture level within the cladding despite varying outdoor conditions.

* EIFS with drainage and a liquid applied water-resistive barrier coating readily disperse liquid water and moisture introduced by flaws in the building envelope.

* Liquid-applied, water-resistive barrier coatings outperform sheet goods. In addition, EIFS with water-resistive barrier coatings performed significantly better than other claddings that used building paper or spun-bonded polyolefin membranes.

"The data were collected in two phases," says Klamke. "In Phase I there were 15 exterior cladding configurations integrated into one side of the building between January 2005 and March 2006. The goal was to have all of the claddings exposed to similar weather conditions for a year."

The hygrothermal performance was evaluated for three EIFS including liquid applied water-resistive barrier coatings that handle rainwater penetration or condensation due to vapour pressure gradient changes; and ventilated exterior claddings intentionally ventilated (open at top and bottom) and drained to allow air to move freely behind the cladding and increase drying potential.

Phase II simulated building envelope defects that were introduced into some of the wall panels. The goal was to assess the performance of cladding assemblies to water penetration; impact on the performance of wall systems from wall orientation on moisture infiltration, and types of water-resistive barriers used (e.g. sheet barriers versus liquid applied) and different exterior cladding systems (e.g., EIFS, brick).

The best performing wall configuration with respect to positive heat flux during the cooling months (keeping heat out) was EIFS with towelled applied water-resistive barrier coating applied behind the EIFS ventilated wall. The second best was EIFS with a towelled applied water-resistive barrier coating applied behind the EIFS. The best performing wall configuration with respect to moisture management was the EIFS panel with four inches of insulation outbound of the sheathing. The walls with stucco and brick showed high relative humidities at the insulation/gypsum interface during the winter months.

In Phase II, EIFS drainage layers comprised of vertical ribbons of adhesive and a fluid-applied moisture barrier provided the most effective method for managing bulk water intrusion into the cladding cavity.

In Phase I, the wall systems with highest sheathing relative humilities evaluated were stucco (both 3-coat and 2-coat), followed by brick and cementitious cladding. The results demonstrate that towel applied, water-resistive barriers outperformed the other membranes studied.

"The results of the ORNL study show that that EIFS are more capable of controlling temperature and moisture within the wall system than the other exterior claddings that were evaluated," Klamke commented. "What's more, EIFS are better at striking and maintaining the fine balance of moisture and temperature control that is indicative of a well designed, properly operating, energy-efficient building."

John Edgar, Technical Manager - Building Science for Sto Corp and chair of the building envelop subcommittee for EIMA has worked in both Canadian and US EIFS markets for over 30 years. He says that the primary benefit of the ORNL study in the Canadian market is its ability to provide reliable data for use in computer modelling systems, that can then be extrapolated to accurately assess the use of EIFS in any climate.

"We were able to take data about the characteristics of the materials used on the building and put them into WUFI and Moisture Expert. If you run both computer models and they predict what actually happened, it validates the computer models. That way if an architect is trying to evaluate a wall mass in Canada and runs WUFI, he can be confident the program will be accurate. So far the results are really close. It's quite impressive."

In its second year, the study created a "defect" consisting of a 24" gutter mounted over the test panel. Rain water was collected and drained into the wall from the two-foot gutter, via a measuring device called "tip bucket". The size of the gutter is consistent with drainage test opening in the ASTM E-2273-03 standard for testing EIFS drainage efficiency. The panel with the flaw was matched with an identical panel without a flaw. It allowed a direct comparison to see if the flaw led to the wall sheathing getting wetter. With EIFS, it didn't. The real performance studied in the field conditions parallels drainage research conducted at Forintek Canada for CMHC.

"CMHC has done a drainage study about EIFS and horizontal siding. It looks at different types of horizontal siding (vinyl, wood, composite) and different drainage assemblies with paper, SBPO and fluid-applied membranes; drainage mats, 19 mm wood strapping, vertical adhesive ribbons for EIFS or having the siding tight against wall. Out of all of them, EIFS tended to drain the best."

Edgar says facilities in Vancouver, Washington State and at the University of Waterloo are all conducting cladding studies, some with EIFS, that are proving the system's ability to perform and providing much needed data that simply had not existed up to this point.

While the building code for Canadian coastal areas requires 10 mm gap for proper drainage, the ORNL and CMHC research shows that much of a gap may not be needed. "In Canada there is a suggestion that you need a 10mm capillary break for water to drain in coastal climate zones based on moisture index, but there is no testing research to say that is a fact," says Edgar. "The CMHC and ORNL studies show that a smaller gap drains more efficiently than a larger one when the drainage cavity materials are non-absorptive."

In nutshell, the objective is to keep water out of a wall," says Edgar. "But when it does get in, there can be problems. That's why the focus is on what is happening to wall assemblies when water gets past the outer cladding. "

Edgar says that what surprises people the most is that EIFS is so effective - not that it's a little better; it's dramatically better.

"Some preliminary requirements from CCMC for measuring drainage efficiency in EIFS clad walls are that the wall assembly should not retain more than a thimble of water per M2 over a 48 hour period. There isn't a cladding system in the world that can do that besides EIFS."

For more information visit <www.eima.com>.