Success With EIFS, continuedWindow flashings and joints. Wherever a window, a door, or an electrical or plumbing fixture interrupts the EIFS surface, a proper joint must be constructed. Create a caulked joint at the EIFS surface; beneath the caulked joint, integrate a reliable flashing into the secondary weather barrier.

Window leaks account for the majority of water damage in EIFS houses. The EIFS itself isn’t usually leaking; instead, water is entering between the window and the EIFS, or the window itself is leaking water. The solution requires a window flashing that works, as well as a correctly detailed joint between the window and the EIFS wall.

On a lot of job sites, one subcontractor installs the windows, and another installs the EIFS. The EIFS contractor usually puts up the building paper before attaching the foam board, but he can't flash the windows, because those get installed before he comes onto the job. So we devised a flashing detail for the window installer that allows the EIFS installer to tie the flashing into the building paper later (Figure 6).

Figure 6. Window openings must be effectively flashed in a way that lets the flashing be tied into building paper or housewrap that is applied after the window is set. The authors recommend covering the sill framing with a layer of peel-and-stick membrane, then placing a one-piece welded metal pan over the sill membrane. Next, side pieces of peel-and-stick can be installed to lap over the ends of the metal pan for a watertight assembly. The paper backing is left on the edges of the membrane, so that the membrane can later be sealed over the building paper or housewrap drainage plane used to cover the wall sheathing.

It uses strips of peel-and-stick flashing membrane for the bottom, sides, and top of the window, all tied into a soldered metal sill pan that is easily made to order by a metal shop. We leave the paper backing attached to the peel-and-stick at the sides and bottom of the window; that way, when the EIFS contractor attaches paper or other membrane to the building, he or she can seal the membrane over the barrier for a watertight assembly. The EIFS is then installed over the drainage material, and the joint between window and EIFS must be sealed (Figure 7). Surprisingly, on many houses we investigate, none of the joints have any sealant at all. Typically, the owner didn't want the look of the sealant, and the contractor didn't think sealant was needed. On jobs we supervise, we explain to the owner that a well-sealed joint is a requirement to prevent a costly failure, and we detail one joint for them so they can see how it looks. Generally, once they understand the risks, they'll agree that the appearance is acceptable for the sake of performance.

Figure 7. This joint between the EIFS and the brick-mold window casing should be sealed with backer rod and silicone sealant. Apply sealant to the base coat before the finish coat is applied. Be aware that many windows allow water to pass between the casing and the sill or jamb, so that surface joint sealing provides only partial protection. To protect the sheathing and framing, the secondary weather barrier and window flashing must be in place beneath the EIFS and the window.

A proper joint needs to have a sufficient gap, with backing and sealant. The rule of thumb is that the joint space should be four times the anticipated movement — so, if you expect 1/8 inch of movement, you would need a 1/2-inch gap so that the sealant would be able to flex. At windows, most manufacturers call for a 1/2-inch gap in their written specs. In practice, however, there isn't much movement at window joints, and a 3/8-inch joint is often sufficient. As important as the gap size is the quality of the surface. Sealant has to be applied to the base coat, not the finish coat, because in moist conditions, the finish coat itself will often suffer cohesive failure and come apart under stress, allowing the joint to open up. Also, the base coat has to be thick enough to fully cover the mesh — a big reason to apply the base coat in two layers, especially at panel edges. Behind every sealant joint, there must be backer rod. This lets the sealant stretch between the sides of the opening without sticking to the back. Penetrations such as hose bibbs and electrical boxes should be sealed just as thoroughly as windows, with a flashing tied into the drainage plane, as well as a surface seal where the EIFS meets the attached element (Figure 8).

	Figure 8. All penetrations should be flashed beneath the EIFS, as well as surface-sealed at the joint. In this example, peel-and-stick membrane is used to seal the electrical box to the housewrap (top left). A gap is left between the EIFS and the box (top right), and the gap is then filled with backer rod and sealant (center left). Hose bibbs (center right, and left) receive a similar treatment.

Aesthetic joints. When the finish coat is being applied, the installer has to run it continuously, keeping a wet edge; if the coat dries out in the middle of the process, there will be a visible cold joint. You can't run the finish more than a limited amount of square feet before it dries out, so the installers cut a V-groove in the foam as a stopping point. This "aesthetic joint" lets the installer work within a manageable area without causing cold joints. Aesthetic joints can't occur at an EPS board joint — they can cross a board joint, but not line up with it. Also, the aesthetic joint can't be routed too deep, or it will cause a crack. At least a 3/4-inch thickness of EPS board has to remain when the joint is made.

Aesthetic joints are coated with base coat and reinforced with standard or lightweight detail mesh. The process requires care: The installer should use a specialty trowel to embed the mesh, because standard trowels may cut the mesh.

To EIFS or Not to EIFS?

When people ask us, "Should we use EIFS on our building?" it always makes us stop and think. It's important to distinguish between barrier EIFS and drainage EIFS. Our company uses both, and we're comfortable with the risks. However, we are experts in the system, and even we have to work to avoid problems. We know what the materials issues are, but not every product in the market has been thoroughly tested. We also know what the problems with details and installation are, but we can't be on every side of the building 24 hours a day to make sure every task is done right. The fact is, barrier EIFS can be troublesome. If you don't understand it well, and if you aren't extremely careful, you are risking problems. Drainage EIFS, on the other hand, can be as reliable as traditional claddings — it all depends on how well the secondary weather barrier is installed. In fact, that secondary weather barrier is critical under almost any kind of siding. Our company has gotten a lot of calls on moisture and rot problems under traditional stucco. We've also investigated houses with wood siding in the same parts of the country that were hit by widespread EIFS failures, and found the exact same kinds of destructive water damage. Anyplace where buildings see rain — especially heavy, wind-driven rain — it all comes down to the secondary weather barriers and flashings. If you install that system right, the building will be protected no matter what siding material you use; and if you don't, you can expect trouble under any siding material. The problem is that a lot of people have been installing weather barriers and flashings poorly. On the other hand, EIFS itself has vulnerabilities some cladding systems don't have. One issue is that the EPS board can act like a sponge, holding water against the building, and that's not really true of other claddings such as vinyl or clapboards. The second thing is that EIFS is a tight system — not tight enough to keep every drop of water out (because often there is a penetration or flashing defect allowing water in behind it), but tight enough that it doesn't breathe well at all. With EIFS, there is very little drying potential — so even relatively small amounts of wetting can lead to some trouble. Success with drainage EIFS requires special attention to the secondary weather barrier, as well as painstaking attention to the water-shedding surface details. And there's no doubt that a proper EIFS job costs more than a hurried job with thin base coats and careless joint sealing. Typically, the details and extra care we require add $2.25 or more per square foot to the cost of the system. For example, we supervised a 100,000-square-foot EIFS job in Montgomery, Ala., that was bid at $525,000 before we became involved. After we explained that the contractor would have to follow all the manufacturer's requirements, and that the EIFS application would be inspected, the price went up to $825,000. That was a little steep, but installers do have to charge a premium for careful work. So if you use EIFS on a building, don't lock your installer into a cheap bid — you'll get a system that is likely to suffer water damage. Don't look at EIFS as cheaper than more traditional claddings. If you want the cheapest cladding system, use something besides EIFS. And regardless of the siding system you choose, pay attention to the weather barrier beneath the siding. That's what is really protecting the building.