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EIFS Drainage systems:
This article discusses in-wall drainage systems introduced to avoid moisture and mold problems in EIFS synthetic stucco wall systems, and the role of weather and moisture in stucco wall installation, durability, and painting success.
This article series discusses best practices construction details for building exteriors, including stucco exteriors, exterior caulks and sealants, and choices and application of exterior finishes on buildings.
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Continuing from from Best Practices Guide to Residential Construction we discuss the introduction of drainage systems intended to reduce or avoid these EIFS difficulties.
In response to these problems, most EIFS manufacturers have introduced new “drainage” or “water-managed” systems, which require the same type of waterproof drainage plane found behind traditional stucco systems (see Figure 1-30)
[Click to enlarge any image]
As with traditional stucco, layered building paper or plastic housewrap protects the framing and sheathing, and all exterior openings and penetrations are flashed to conduct any water to the outside of the sheathing wrap.
Since window leakage was the single biggest contributor to EIFS failures, pan flashing is recommended at windows.
Rather than gluing the EPS foam to the sheathing, the new drainage EIFS typically use mechanical fasteners and are designed with a capillary break between the back of the EPS and the sheathing wrap to promote drainage.
Some EIFS contractors use special corrugated or wrinkled sheathing papers to create the drainage space, while others have vertical grooves cut into the back face of the foam insulation.
In all cases, the drainage plane leads to a perforated weep flashing at the foundation to drain away any trapped water.
The backup drainage layer, however, should not provide an excuse for sloppy workmanship on the exterior skin. The new kinds of EIFS should still be made as waterproof as possible, since any water that leaks past the skin may be slow to dry out. EIFS consultant Russell Kenney, who has worked with these systems for nearly 20 years, recommends exceeding the minimum specs required by EIFS manufacturers.
On the other hand, our EIFS damage photograph (left) shows how water or moisture traps can form in an EIFS wall even in a building interior, leading to substantial damage. (Photograph courtesy of home inspector John Rudy).
Kenney recommends a higher-density EPS foam with only 2% water absorption by volume instead of the 4% allowed by ASTM C584. In addition, Kenney recommends a heavier 6-ounce reinforcing mesh versus the typical 3-ounce cloth, as well as special high-impact mesh in high-traffic areas.
He also recommends a 3/32-inch base coat applied in two layers, with the first layer used to partially embed the fiberglass reinforcing and the second layer to fully cover and protect it.
These steps will significantly improve the impact resistance of EIFS, but it is still less durable than traditional stucco or thin-coat stucco.
See details about the cause, diagnosis, cure, or prevention of paint failures on stucco exterior walls, found at STUCCO PAINT FAILURES.
As with the original barrier EIFS, all penetrations require a high-quality elastomeric sealant. The sealant needs to be applied to the base coat since the finish coat tends to soften when wet, providing a poor substrate for sealant. For the caulk joints to last, they must be wide enough to tolerate the anticipated movement, typically 3/8 to 1/2-inch, and backed up by backer rod (see “Joint Design,” page 37 in Best Practices Guide to Residential Construction).
While control joints are generally not needed along the length of the wall—unless it exceeds 75 feet and is in direct sun—they are required between floors on multistory buildings. Silicone sealant is recommended at all joints for its longevity and flexibility in cold temperatures.
In theory at least, drainage EIFS should function the same as any other exterior cladding systems. Any water that manages to penetrate the outer skin should be stopped by the drainage layer and safely drained away. However, given the low permeability of polymer-based coatings and the tendency of EPS foam to soak up and hold water, EIFS are best avoided in residential projects unless high-quality workmanship and regular maintenance of sealants can be assured.
-- Adapted with permission from Best Practices Guide to Residential Construction.
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