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EIFS Design and Detailing

Regardless of whether one chooses to design with a traditional Class PB EIFS or with EIFS—the next generation, a vital component for long term durability and life safety is construction detailing. “As much as 90 percent of all water intrusion problems occur within 1 percent of the total building exterior surface area. The 1 percent of the structure’s façade contains the terminations and transition detailing that all too frequently lead to envelope failures.”6 With this in mind, design criteria and detailing considerations for EIFS are listed below:

1. Wind Load—design for maximum allowable system deflection, normal to the plane of the wall, of L/240. This is a basic requirement for stiffness of the supporting wall construction. The EIFS manufacturers code evaluation report and/or independent tests should be checked to determine design pressure limits.
   
   
2. Moisture Control—prevent the accumulation of water behind the EIF system, either by condensation or leakage into the wall construction, in the design and detailing of the wall assembly. This is accomplished in three ways:
   
   i.) by providing flashing above window and door heads, beneath window and door sills (Figure 4), at roof/wall intersections (Figure 5), decks, abutments of lower walls with higher walls, above projecting features, and at the base of the wall, such that water is directed to the exterior, not into the wall.
   
   

   Figure 4. Sill flashing is provided beneath potential leak sources such as windows to direct water to the exterior, not into the wall assembly. The fluid applied membrane protects the rough opening. The inner seals beneath the window, at the back leg of the pan flashing, and along the jamb interface, function as air seals to reduce the effect of pressure differential, one of the driving forces of water intrusion, at seams in the construction.

   ii.) by controlling air leakage in cold climates to prevent water vapor in moist air from condensing and being deposited inside the wall assembly. EIFS—the next generation includes an air barrier behind the EIFS on the supporting construction. Note, however, that air barrier continuity is necessary to prevent excess air leakage. Thus, adjoining components in the building envelope assembly—windows, doors, and roof membranes—must be connected to the EIFS air barrier. The effects of air tightness on mechanical ventilation requirements and indoor air quality should also be considered in the overall project evaluation.
   
   

   Figure 5—critical details such as roof/wall intersections must include diverter flashing that integrates with the exterior wall covering such that rain water is directed to the exterior, not into or behind the exterior wall covering.

   iii.) by minimizing the risk of condensation in the wall assembly caused by water vapor diffusion. In the event condensation is identified in the wall assembly, increasing the thickness of insulation will generally move the dew point outward to a safer location in the wall assembly or eliminate it altogether. In any event one should generally avoid the use of vapor retarders on the interior side of the wall in warm, humid climates. The vapor retarder has the effect of inhibiting drying in the event of incidental moisture intrusion, and can potentially cause damage to interior wall components should water vapor condense behind them. In general condensation has not been a significant source of moisture accumulation in EIFS clad walls. By far, the largest risk of water damage in walls is bulk water entry from rainfall and leaks associated with poorly designed or improperly constructed details.
   
   

   Figure 6. Expansion joints are required at floor lines in construction where floor line deflection is anticipated. In this case a nested stud in the structural frame assembly accommodates deflection. The EIFS wall covering must also include a joint to accommodate the movement. In wood frame construction joints are similarly required to accommodate anticipated movement caused by cross grain shrinkage of wood joists.

3. Impact Resistance—EIFS impact resistance can be greatly enhanced by adding a layer of reinforcing mesh to the standard grade of mesh. Areas subject to abuse such as ground floors, entrances, columns at carports, etc., should receive the extra mesh layer to a minimum height of 6'-0" (1.8 m) above finished grade. Impact resistance is classified by EIMA as Levels 1-4, with 4 being the highest impact resistance level. Where additional impact resistance is required, contract drawings should indicate the locations on elevations.
   
   
4. Color Selection—select finish coat with a light reflectance value of 20 or greater.
   
   Light reflectance is a relative measure of lightness of a color. The higher the number on a scale of 1-100 the lighter the color. The use of dark colors (lightness value of less than 20) is not recommended with EIF Systems that incorporate EPS. EPS has a service temperature limitation of approximately 160ºF (71ºC) and sustained exposure at this level or higher could result in deformation of the EPS and delamination of the EIFS coatings. Consideration should also be given to light reflective surfaces such as mirrored glass, or white concrete in full sun, which can reflect sunlight onto an EIFS wall surface and increase surface temperatures.
   
   
5. Joints are required at the following locations in EIFS wall assemblies:
   
   i.) where they exist in the substrate or supporting construction
   
   ii.) where the EIFS adjoins dissimilar construction or materials (Figure 7)
   
   iii.) where pre-fabricated panels abut one another
   
   iv.) where the substrate changes
   
   v.) at changes in building height or where other significant changes in building shape or structural system occur that could cause differential movement
   
   vi.) at floor lines in multi-level wood frame construction (Figure 6)
   
   

   Figure 7. A two stage joint sealant design can be accomplished with a primary outer seal and secondary inner seal (barrier membrane). Note, the fluid applied membrane, although not shown behind the adjacent cladding in this case, can also take the place of the traditional moisture protection behind the adjacent cladding.

   In addition to the above joint locations, wherever the EIFS terminates at abutting elements such as windows, doors, fixture penetrations, and dissimilar materials, a joint must be provided between the adjoining materials (Figure 4). Joints should be sealed with compatible backer rod and sealant that has been evaluated in accordance with ASTM C 13827. Joint sealants tested in accordance with this method are subjected to harsh exposures that enable the specifier to verify joint performance under an array of environmental conditions. Consideration should also be given to joint designs with secondary moisture protection and drainage to the exterior (Figure 7). Such two stage joint designs can minimize maintenance associated with sealants, particularly on mid or high-rise structures.
   
   

6. Grade Condition—do not specify EIFS below grade (unless the system is especially designed for use below grade) or for use on surfaces subject to continuous or intermittent water immersion or hydrostatic pressure. EIFS is a finish material intended for use as a vertical above grade wall covering. It should be noted that in recent years some codes have prohibited the use of foam plastic below grade because of the potential for termites to migrate undetected behind foam plastic insulation.
   
   
7. Trim, Projecting Architectural Features and Reveals— all trim and projecting architectural features must have a minimum 1:2 [27º] slope along their top surface. All horizontal reveals must have a minimum 1:2 [27º] slope along their bottom surface. Slope should be increased for northern climates to prevent accumulation of ice/snow and water on the surface. Where the trim/feature or bottom surface of the reveal projects more than 2 inches (51 mm) from the face of the EIFS wall plane, the top surface should be protected with waterproof base coat to supplement the standard base coat. The use of trim and features that exceed the maximum allowable thickness of EPS permitted by code (typically 4 inches [100 mm]) should be avoided. Periodic inspections and increased maintenance may be required to maintain the surface integrity of EIFS on weather exposed sloped surfaces. Therefore limit projecting features to easily accessible areas and limit total area to facilitate maintenance and to minimize the maintenance burden that can be associated with such features.
   
   Lastly, for large weather exposed projecting features such as ledges or cornices, the feature should be built out with framing or other structural support and protected with metal coping or flashing.
   
   
8. Fire Protection—for Types I, II, III and IV construction do not use foam plastic in excess of 4 inches (100 mm) thick unless it is specifically recognized in the EIFS manufacturers code evaluation report or approved by the code official. Where a fire-resistance rating is required use EIFS over an existing rated assembly and refer to the manufacturer’s applicable evaluation report for limitations that may apply. EIFS is considered not to add or detract from the fire-resistance of a rated assembly.