EIFS has been intensively designed and developed for use on exterior vertical walls, but sometimes it finds itself being used in other ways, such as in soffit and ceiling applications outdoors. When used in this matter, the EIFS finds itself turned upside down. Some unorthodox uses for EIFS turn out just fine, but in other instances these uses can be dangerous.
Soffits and ceilings provide EIFS with sort of a reversed composure, although the installation is basically the same, only upside down. Instead of being attached to substrate vertically, it's hanging from substrate horizontally. In ceiling or soffit applications, the EIFS can be installed one of two ways. It can either be attached via an adhesive to the substrate, or mechanically fastened through the foam and into the substrate.
As with any non-exterior wall application of EIFS, the first concern is fire, and EIFS can use either expanded polystyrene foam (EPS), extruded polystyrene foam, (XPS) or polyisocyanurate foam. EPS and XPS are both thermoplastics, meaning they get soft, melt and flow when heated. EPS has an especially low melting point when it comes to foam plastics but it can also catch fire. Polyisocyanurate foam does not melt when heated, but degrades instead and can also still catch fire.
Most soffits will be placed near a window, or will have a window directly below them. This can have several dangerous consequences if there's a fire. Fire can exit a home through the windows, where it will easily travel upwards to reach the soffit. The EPS foam inside the EIFS will then melt and begin to drip down. Worse, the entire soffit can lose all of its structural support and fall off of the house while still smoldering. Polyisocyanurate foam may not melt, but it can still catch fire.
EIFS can only be installed outdoors, regardless of the application. Indoors, it is almost always against fire codes because the EPS foam is combustible, and doesn't meet the necessary 15-minute burn time as specified for indoor foam plastic uses by fire codes. Outdoor ceilings can present the same issues as soffits, and pose more of a danger of collapsing due to their larger span.
Building codes and EIFS ceilings and soffits
Building codes are not overly specific when it comes to building ceilings and soffits out of EIFS, which is odd considering this method takes a barrier system and then installs it upside down. Some building codes, however, do indeed specify that drainage EIFS must be used in certain places like Richmond Hill, Burlington and Oakville, Ontario. Obviously drainage EIFS can't be used on soffits, so this makes things a little confusing when deciding how to go about installation and what materials to use.
Other risks when installing EIFS upside down
If the distance between the end of the EIFS soffit and where it affixes to the wall is wide, structural problems are more likely to occur. The longer or wider the soffit, the more in danger the soffit when made of EIFS is in of collapsing. Depending on the substrate, the soffit might also sag or hang unusually. The soffit is also supported by lightweight framing, and due to the lightness of EIFS, can get caught up in wind and bend upward, placing excess stress on the joint.
Solutions to issues with installing EIFS upside down
Building soffits or ceilings with EIFS that aren't wide and don't need as much support might create a safer soffit or overhang. More layers or heavier grade reinforcing mesh can also be used, and mechanically fastening the EIFS to the substrate may also provide more structural integrity to EIFS soffits and ceilings.
However, some of these applications of EIFS are not recommended by manufacturer's instructions, which also as always can void a warranty on the EIFS components. These solutions also do not solve the issue of the fire danger to EIFS soffits as fire will always plume upward, creating a dangerous situation when using EIFS overhangs, ceilings and soffits. When in doubt, it's better to just leave EIFS soffits, ceilings and overhangs out of the design when possible.