EIFS was originally developed for—and intended to be used on—vertical exterior walls. It is not a roofing material, nor is it a below-grade insulation or waterproofing material. It is also not well suited to large sloped surfaces such as windowsills, especially when the slope is shallow. While it’s true that EIFS can be applied to such surfaces, and does occasionally fare well, it’s not really what EIFS is for.
But what about upside-down surfaces such as soffits and ceilings? EIFS is used this way all the time.
EIFS, as originally promoted in North America, used only expanded polystyrene insulation. Most of the EIFS now in place in North America uses EPS. EIFS that uses polyisocyanurate (“polyiso”) foam came later, and is used mostly on residential EIFS applications. From the standpoint of physical properties, EPS and polyisocyanurate are two different animals. Since EPS is the more common insulation material, the discussion will begin with this.
Definition of plastic components
Plastics can be characterized in several basic ways. One is whether they get soft (thermoplastic) or do not get soft (thermosetting) when they get hot. EPS is a thermoplastic type of plastic. Thermoplastic plastics, when heated, melt before they burn. When heated, thermoplastics get soft, and then become a liquid and flow. Thermoplastics lose all their structural characteristics in this heated state. When cooled, they become hard again. Keep in mind that EPS is mostly air. Thus, when it melts, its volume reduces to that of the plastic resin that forms the beads from which the insulation is made. EPS loses most of its strength below 200 degrees F, so it doesn’t take a lot of heat to melt EPS. Also, extruded polystyrene, such as Styrofoam, is the same as EPS in terms of its melting characteristics.In contrast, polyiso foam is a thermosetting type of plastic. It chars and degrades when it gets hot, rather than melting. Polyiso retains some of its physical strength while in this elevated temperature phase. Both types of plastic, if they get hot enough, can burn.
When used in an upside-down application, such as a soffit or ceiling, EIFS is essentially hanging from the substrate to which it is attached. In the case of adhesively attached EIFS, the topside of the foam is attached to the substrate via the adhesive. In mechanically attached EIFS, the foam is attached by a fastener that goes through the foam and into a structural material above the EIFS. Keep in mind that the fastener does not go through the reinforcing mesh, but only through the foam.
One of the concerns with using EIFS in an upside down application is fire. If a fire occurs in a room and the flame exits the room through a window, the flame plume travels upward. If there’s EIFS above the window, such as an EIFS soffit, the soffit gets hot. The heat then travels quickly through the thin EIFS lamina and heats the foam. If the foam is EPS, it melts. Once it melts, then the EIFS lamina is not supported by anything; it is free to sag. If it sags enough, it can split open and fall off, exposing the foam to direct flame impingement. The foam might even catch on fire.
It doesn’t take a lot of intuition to realize that the wider the soffit, the more this is a problem. This is because the parts of the EIFS lamina that are connected to anything other than the foam could be many feet away. Thus, for expansive ceiling applications, the EIFS lamina “ceiling” would tend to sag even more when spanning great distances. With polyiso foam, this basic problem still exists, but the fact that polyiso does not melt per se, helps a bit. Many polyiso EIFS systems are mechanically attached, which also helps. Polyiso is also stiffer than EPS, and also tends to sag less than EPS for that reason.
What do the codes read?
The codes provide very little information about using EIFS in an upside-down configuration. They should, as the problem is obvious and has been known for years. True, there are drawings in the technical reports, issued by various code agencies to various EIFS producers, that show various small “returns” above windows using EIFS, but this is hardly the basic problem. The basic problem occurs when the span of the EIFS is large. The span, in this case, is the horizontal distance between the points at which the EIFS is attached to its supporting structure, other than through the foam insulation.One way to improve the sagging problem would be to use extra layers of reinforcing mesh. This would tend to hold the lamina together better. Another would be to provide intermediate, direct connections of the lamina to the wall structure, thus reducing the span. This would involve breaking down the EIFS surface into discrete areas and tying the EIFS back to the substrate at those areas. This would eliminate the desirable seamless appearance of the surface but would help the sagging problem. Another would be to run the EIFS mechanical fasteners through the reinforcing mesh. Most EIFS producers do not allow fasteners to be installed this way, as it can lead to cracking and other problems with the lamina. However, there’s little doubt that it wouldn’t help the sagging issue.
Fire is not the only concern—there are structural issues too. Often, ceilings and soffits are supported by light framing systems. The framing is hanging from the structure above by wires or by solid framing. When used outdoors, the upside-down surface is exposed to wind uplift forces. These forces can be sizeable and act to lift the soffit or ceiling vertically. Being a lightweight material, EIFS does not have much weight to resist being pushed upward. In addition, if the framing the supports the EIFS is not rigid, the whole substrate assembly (the EIFS, the framing and the substrate), can be lifted upward. This can cause the soffit or ceiling to flex, which can, in turn, cause the EIFS to crack.
All the above information applies to exterior applications of EIFS. Interior use of EIFS, whether on walls or ceilings, is definitely a no-no, as the codes specifically disallow such uses. The reason is that the EIFS lamina does not provide the 15-minute fire protection required by the code for interior uses of foam plastics.
What can you do about this? If you’re a contractor and see questionable upside-down applications of EIFS, bring the issue to the attention of the building designer. If you’re an architect or specification writer, talk with the suppliers of EIFS that you are considering using. If you are an EIFS producer or trade association that deals with EIFS, look into this matter with a goal of understanding the dynamics of this issue, and then do something about it, such as testing to determine the limits of what performs well, or by issuing product use guidelines. As for myself, as an EIFS consultant, I always raise this as an issue when doing reviews of drawings of new EIFS buildings, or when visiting old ones.
Lastly, here’s a question that has come up more than a few times: If the codes require a drainage-type EIFS on a particular building, and EIFS is used as a soffit or ceiling, than is drainage required on the upside-down locations too? And if so, how is the drainage accomplished? I have had building officials raise this issue by pointing to documents that do not say that you CAN do soffits or ceilings with EIFS. Perhaps the codes need to clarify that drainage is needed only on exposed vertical surfaces. W&C
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