Exterior insulation and finish systems (EIFS) combines foam insulation and lightweight stucco to achieve an attractive and durable exterior finish. EIFS is an excellent solution for insulating uninsulated masonry walls. EIFS is installed on the exterior of buildings, and takes the place of exterior siding or stucco. Since EIFS installs on the exterior covering the entire wall, it greatly reduces thermal bridging through the wall’s structural members.
EIFS looks like masonry stucco and is made up of three layers.
- The bottom layer includes one-inch sheets of expanded polystyrene foam board, also known as bead board. These sheets are fastened to the masonry wall or wood wall sheathing. This insulating foam gives EIFS its high R-value: about R-4 per inch. EIFS applications use from 1 to 6 inches of foam insulation, which adds R-4 to R-24 to the exterior wall.
- The middle layer is made of acrylic coatings that are troweled onto the foam board. Multiple coats and reinforcing fabric may be installed over the seams, at doors or windows, and at corners and other transitions.
- The top coat is made of acrylic coatings that are troweled over the base coat. The top coat contains pigments to provide a final color, and sand to give it texture. The coarseness of the sand and the technique used to apply the top coat can be varied to produce a variety of textures.
Special care is needed to assure that water doesn’t get behind EIFS installations. Problems have cropped up in the past when poor sealing above doors and windows allowed water to leak behind the EIFS. If you choose EIFS for your home, be sure to ask how sealing will be accomplished at these critical junctions.
Residential Energy: Cost Savings and Comfort for Existing Building contains more information on EIFS.