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).
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
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
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
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).
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
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
Russell J. Kenneyis the founder and director of R.J.
Kenney Associates, Inc., of Plainville, Mass., whereMichael E. Kenneyis the director of field services. The
firm specializes in EIFS investigations, remediation,
supervision, inspection, and design review.