EIFS (Exterior Insulated Finish System) is one of the most energy efficient siding choices that a homeowner can choose from. The combination of a thermal barrier as well as an excellent air barrier is a vital combination in reducing the overall energy usage of a home. However, there are EIFS board manufacturers that produce foam board of lesser quality that is considered to code, but should not be used if the homeowner wants the EIFS to last a life time.
EIFS Foam Board Insulation
All foam board insulation materials are not created equal. Extruded polystyrene (EPS) is a generic term for white foam board that is pressure compressed into sheets, blocks, and balls that are used for a variety of insulation and craft projects around the world. EPS comes in a multitude of different densities and most EIFS manufactures wrap the edges not to avoid litigation because some contractors do not install the EIFS correctly is they install it.
EIFS Foam Board Issues
EPS foam board insulation and sun light do not get along. In fact, EPS left exposed to the sun for more than 90 days is considered unusable by building code standards. What will happen is the sun will break down the polymers of the foam board and weaken their bond to each other. The result is that the foam board falls apart, literally in your hands. Even foam board that sits exposed to the sun for more than a month is greatly affected by the sunlight. This is why it is extremely important to get the base coat installed as soon as the foam board is up on the exterior surface. If the base coat is installed over bad foam board, the surface of the EIFS will prematurely crack and will not be able to be repaired using conventional methods.
Moisture retention has been an issue with EIFS over the years and is due to improper flashing, caulking, and insulation techniques. The foam board provides and exterior vapor barrier. Building code requires a vapor barrier on the inside between the drywall and the framing. Have two vapor barriers on each side creates vapor lock and will not allow moisture accumulation to escape the cavity. This can cause huge mold and mildew problems and has been the discussion of several lawsuits in the past 20 years.
EIFS systems are a fantastic thermal barrier, but must be installed correctly and in a timely manner. This is something to consider if you are looking at having EIFS installed on your house.