For 30 years, the stucco-like appearance of Exterior Insulating and Finish Systems (EIFS) has given commercial buildings high curb appeal, broad design and color flexibility, low maintenance and durability, and high energy efficiency. In more recent years, the residential marketplace has begun enjoying the benefits of EIFS, as well. But in some residential applications, there had been a problem.

Moisture that had passed through windows and door openings was trapped behind the EIFS exterior; in some cases the moisture caused rotting of wall studs and sheathing. The problem was summarized in the New York Times article, "Some Users of Artificial Stucco Find Headaches Are Real", : "The trouble is that EIFS are too waterproof. Water that gets trapped behind [the EIFS exterior] has nowhere to go and begins soaking into studs or plywood sheathing."

For this reason many EIFS manufacturers have innovated moisture-mitigation systems that effectively prevent moisture buildup on the rare occasions that moisture makes its way behind the EIFS exterior.

Potential Moisture Problems of Barrier EIFS

A traditional EIFS exterior wall is comprised of EPS foam, fiberglass mesh and a cement-like stucco material. The first step in creating an EIFS exterior is to glue a layer of EPS foam directly onto the sheathing of a house or commercial building. Then, a base-coat of cement is applied, followed by fiberglass mesh and a finish coat of cement. This type of system is called a face-sealed barrier EIFS. It resists water penetration at its outer surface.

But what happens if door openings and windows are of poor quality and allow water to penetrate them? What happens if the EIFS windows and door openings are not properly caulked and sealed? According to many experts, moisture may be able to penetrate these areas and get trapped behind the wall.

"Rainwater and wind-driven rain can work their way past the acrylic polymer coating and the foam insulation glued directly to the wood framing and sheathing members of your EIFS-clad house," says Tim Carter, who writes the nationally syndicated "Ask The Builder" column. "Once the water becomes trapped between the wood sheathing and the foam insulation, rot problems begin."

Such problems were the subject of a news story aired April 1999 by Dateline NBC. The report tested three EIFS-clad homes in North Carolina and found that all three had trapped moisture. But according to Stephan Klamke, executive director of the EIFS Industry Members Association (EIMA), the Dateline report overstated the moisture problems and their cause.

"In the instances where moisture problems did occur [with EIFS], poor quality construction practices and sub-par materials were the cause," said Klamke in a written editorial response to the Dateline report. "Dateline led viewers to believe that the entire wall surface of an EIFS home is likely to experience moisture damage, when, in fact, moisture damage is almost always limited to areas directly adjacent to or under windows."

Introducing the Moisture-Drainage EIFs

Following a similar "flashing and weep hole" strategy used in brick construction, EIFS manufacturers have redesigned EIFS to allow for moisture run-off. Here's how the EIFS moisture-mitigation process works for most manufacturers:

1) An asphalt felt is placed over the sheathing to prevent moisture penetration.

2) Some manufacturers apply a mesh or other medium directly over the building paper to create an opening between the sheathing and backside of the insulation board through which water can escape to the outside. Other manufacturers have added grooves or ridges to the EPS foam to allow water to pass to the bottom of the wall.

3) Metal flashing is placed at the bottom of the wall, around windows and doors and any other place where the synthetic stucco abuts something that is not stucco. The flashing "catches" the water and diverts it to the outside of the EIFS wall through weep holes.

According to the June 1999 issue of Professional Builder, comprehensive testing conducted by the National Research Council Canada and USG Corp. supported the EIFS water-mitigation system as an effective means to prevent moisture build-up.

* Water-managed EIFS-clad walls performed effectively and efficiently handled any water that penetrated the system in tests.

* Any water that breached the exterior skin was stopped at the building paper and directed down and out the wall through the flashing and weep details. The water-managed systems worked even when sealant around the windows was made to fail completely. The EPS located below the windows in this scenario contained no significant amount of moisture.

* Any moisture that remained in the system was effectively kept from moisture-sensitive materials by the sheathing membrane.

Tim Carter speaks positively about the EIFS moisture-mitigation system.

"If you install a new water managed drainable EIFS system on your new home according to manufacturer's specifications," he writes, "you should have no water problems."

Improving Your Curb Appeal

Because the EIFS industry has modified EIFS to prevent potential moisture problems, the benefits of EIFS can be enjoyed without concern about potential moisture problems. For more information on using EIFS-clad exteriors, the National Association of Home Builders Research Center offers two publications: "Quality Plan for the Installation of EIFS" and "Before you Use EIFS." Both can be obtained by calling NAHB's Homebase Hotline at 800-898-2842.

Why Commercial Applications Seldom See Moisture Problems

Commercial EIFS applications account for more than 95 percent of all applications that use EIFS-clad systems, but these applications have seen virtually no moisture problems. In the instances where moisture problems did occur, they were limited to residential construction. There are two reasons why.

According to syndicated columnist Tim Carter, "In commercial construction, the EIFS material was originally applied over concrete block or masonry structures and to buildings that were built using steel or other non-wood products," he says. These materials do not absorb moisture.