Tips for Leak-Free EIFS Details
In my consulting work I often review the construction details for EIFS projects, both for new buildings and old ones. The former is intended to get it right the first time, while the latter is often an effort to find out what went wrong. This month's column contains a sampling of some not-so-obvious details I've seen while doing these reviews.
Vertical aesthetic revealsA lot of EIFS walls are flat, with little or no projections outward from the wall surface. It's quite common, though, for grooves to be cut into the foam, creating "false joints" in the wall for appearance purposes. This type of joint is often called an aesthetic reveal. Vertical grooves present a not-so-obvious condition that can let water in. Here's what happens.
The foam is installed and a router is used to make a groove in the foam from the bottom to the top of the wall. The EIFS lamina is then installed, as is a parapet cap flashing at the top. The flashing overhangs the EIFS enough to keep water from getting blown up and under the flashing ... or does it? What about at the aesthetic groove?
What really happens is that at the flat EIFS wall surfaces, the flashing overhang keeps the water from getting in. It takes several inches of overlap to do so and sealing it with caulking helps further. But at the aesthetic reveal, there's a small area where the flashing is not snug against the EIFS. In fact, the flashing simply goes past the groove and the groove is open to whatever water is in the area.
With wind blowing across the wall, both sideways and upward, water gets concentrated in the groove. Because the flashing isn't tight at that point, the water goes up under the flashing, and can end up on the top of the wall behind the flashing. It's easy to see how water could thus get funneled up inside the wall, leading to leaks.
One solution is to fill the groove with a big gob of caulk. This works for small grooves but sometimes grooves are many inches wide; lots of caulking looks bad, especially if the aesthetic reveal is deep and wide. Here's how to fix it: Stop the groove recess just where the flashing's bottom edge will stop. Detailed this way, the water may get into the groove but when it gets blown upward, it bumps into the end of the groove and can go no further.
This detail is easy to execute when routing out the groove and also doesn't look bad from below. This condition can also occur at other top-of-the-EIFS details, such as windowsill flashings. By the way, the same problem can occur with recessed caulking joints. The solution is simple and similar: Bring the caulking bead out to the face of the EIFS at the point where the bottom edge of the flashing occurs.
Sill flashingsThe use of flashings at windowsills is a good idea. But simply installing a piece of bent sheet metal is not enough. Obviously, long runs of flashing incorporating several pieces of flashing that come together must be sealed where they join. This can be done with cover pieces of flashing, lapping the pieces and other means. However, the end of the flashing run is a different condition.
The end of the flashing needs to be treated so that water cannot run off the end and into the wall. A good way to do so is to turn up the end and to create a dam. This flashing treatment is often called an end dam. The whole flashing needs to slope downward and outward to the face of the EIFS. This makes the water want to flow out and away, rather than ponding.
The flashing also needs to be designed so water cannot get under it. This means having a section of the flashing that laps over the face of the EIFS, or sealing it with caulking, or other means of keeping water out. In addition, the flashing needs to go far enough back into the wall so that if the window leaks, the water will be picked up by the flashing and routed safely to the outside. Depending on the window design, the flashing may have to go all the way to the inside face of the window before the turned-up back edge of the flashing occurs. This inner edge-combined with the end dams-creates a "pan," giving the water little choice but to flow toward the outdoors. But can it?
If you run a continuous bead of caulking all along the sill, then how is the water supposed to drain out? To allow it to drain, small weep holes are needed in the sealant bead. Hardware, such a window and flashing mounting holes, that penetrates the flashing also need to be sealed so that water cannot go through.
Back wrapping vs. edge wrappingBack wrapping refers to tucking the EIFS basecoat between the substrate and the foam at the perimeter of the EIFS. Edge wrapping refers to bonding the basecoat to the edge of the opening or to the web of the track or stud, at the perimeter of the EIFS.
Edge wrapping seals the edge of the panel so that water can not as easily get to the edge of the sheathing. Edge wrapping is common on prefabricated EIFS panels. It provides a strong structural connection of the edge of the EIFS by tying the edge of the EIFS to the wall structure. Edge wrapping does have its pitfalls, though. If used at the bottom edge of an EIFS, any water that gets between the substrate and the foam gets stuck there as it flows downward to the bottom of the EIFS. Obviously, this is not at all what you want with a drainage-type EIFS, as it keeps the drainage system from doing its job.
Edge wrapping at the top of an EIFS panel cannot help keep water from getting into the foam-substrate area in the first place, but can keep it from getting out at the bottom. Thus, the edges of an area of EIFS needs to be considered carefully to determine what kind of edge treatment makes sense for the condition at hand.
For example, flush-mounted windows using back wrapping alone at a window head wind will deposit the drainage water into the window frame. Clearly, a flashing is needed at this point to route the water safely to the outdoors. This flashing should have end dams too, so the water does not run off the end of the flashing at the window jambs.
Hidden sealsSometimes an on-site inspection of an EIFS project will conclude that the perimeter of the EIFS is not sealed at the windows. This often comes from observing that the EIFS lamina butts up directly against he window frame. But is it really not sealed?
It's possible that there is a hidden seal behind the lamina. There's a type of joint sealing material that I call an expanding foam tape. It consists of an open-cell foam material that is impregnated with a viscous mastic-like material. The material comes in rolls like ribbon, in compressed form, and in various widths. When unrolled, it expands to fit whatever gap it is placed in. Emseal and WillSeal are trade names of some of these products.
When used with EIFS, the EIFS insulation is installed first, and a space is left between the window frame and the foam. The tape is placed in the space, and allowed to expand. The EIFS lamina is then applied over the tape and butted into the adjacent wall element, such as a window frame.
Expanding foam tape seals work because they are always pushing back against the foam and the window frame. In a sense, they work like a gasket, by always being in compression. This is different than wet-applied sealants that rely on bonding and extensibility to retain a seal.
Tape seals need to be carefully installed in order to function properly. The space between the window and the foam needs to be of constant width and needs to be sized to make sure that the tape is always pushing back with adequate force. Also, the ends of the tape pieces need to be married together carefully to ensure continuity of the seal. This is especially important at the corners of windows, and where ends of tape pieces stop and start.
Expanding foam tape seals get rave review from architects and building owners because they look good; no sealant is visible. They are commonly used in Europe on all types of buildings, while in North America they are used mostly on residential applications.
Expanding foam tapes seals are a bit pricey, even compared to top-of-the-line wet-applied sealants. No doubt this is a factor in the popularity.
Before you accept someone's opinion that the windows are unsealed, poke around to see if an expanding foam tape seal has been used. Keep in mind that just because a tape seal is there, does not mean it's working right-but at least you can be sure that an attempt was made to seal the joint.
Foam shapesThere are lots of ways of adding pieces of foam to an EIFS wall to create projections from the wall for aesthetic purposes. One way is to make the foam shape thick enough that it goes all the way back to the substrate and is bonded to the substrate. Doing foam shapes this way is complicated as they must be precisely located as the wall is being constructed. The bigger concern, however, is the joint where the EIFS lamina goes from the flat, main wall area to the foam shape.
This abrupt change in thickness concentrates stress at that point and can be a crack location. Cracks can let in water, especially if there is a foam piece seam at that point. This is especially critical on the upper edge of foam shapes, where a ledge is created. Water tends to lay there-right where a crack may occur.
A better approach is to glue the foam shape on top of the main EIFS wall insulation layer. The main foam layer should be basecoated, and then the foam shaped bonded to the base-coat. The basecoat on the foam shape is then married into the basecoat of the main wall area. If a crack occurs at the foam shape-to-main wall juncture, then there's a basecoat behind it to keep the water out. It's also easier to precisely position the foam shape once the main foam layer is in place.
In addition, the foam shape should be the same EIFS product as the main EIFS wall area. Some foam shapes are not EIFS products per se, but rather are some sort of EIFS-like material. Sometimes, these non-EIFS materials have properties that make them incompatible with "real EIFS." This can lead to the development of cracks where two different types of materials come together. When cracks occur, it also raises the question of, "Whose product is at fault?" I do not know of many EIFS producers who formally advocate the use of foam shapes, other than those made using their own products, in conjunction with their bona fide EIFS product.