Construction Concerns: Exterior Insulation Finishing System

Article and photos by Gregory Havel

The exterior insulation finishing system (“EIFS”) in photo 1, below, looks like stucco, but it is not. Traditional stucco is a Portland-cement plaster applied in three layers. Some modern brands are applied as a single layer, and are still basically Portland-cement plaster.

EIFS is a multi-layer polymer (plastic) system. The substrate to which it is attached can be concrete, concrete block (photo 2, below), cement-board sheathing, gypsum-board sheathing, oriented strand board (OSB), or plywood.

  • The base layer of EIFS is the foam-board, varying from 3/4-inch to four inches thick, which is attached to the substrate by troweled adhesive or screwed fasteners with washers, or both. Thicker blocks of foam may be used to create accents, as shown in photo 1. The foam-board is usually expanded polystyrene (EPS) that includes a flame retardant to reduce its ASTM E84 flame-spread rating.

  • Fiberglass reinforcing mesh is embedded in a water-based plastic base coat that is applied to the surface of the foam-board with a trowel, as in photo 2, below.

  • The finish coat of EIFS is a water-based colored plastic material that is applied with a trowel over the fiberglass mesh and adhesive coating. Some manufacturers include some Portland cement in the formula. The finish coat is available in a variety of colors, and can contain texture material, or be textured during application with special trowels. If accents are used, they may be finished in different colors as in photo 1.

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The finished product is resistant to water, sunlight, weather, abrasion, fading, and impact.

Although the completed EIFS system looks like noncombustible stucco, it is combustible. The label on a pallet of EIFS EPS board in photo 3 says “Flame spread rating: 25 or less, per ASTM E84…This insulation board is combustible. Keep away from open flame, welding, and other heat sources. This numerical rating does not necessarily reflect the performance of this or any other material under actual fire conditions.” Although the flame spread rating is low, the smoke produced is dense and black, and can range from 300 to >400, depending on the manufacturer.

Although the completed EIFS system is more difficult to ignite than the exposed foam-board, ASTM E84 tests of the completed EIFS system show results similar to those of the foam-board alone.

The ASTM E84/National Fire Protection Association 255, Standard Method of Test of Surface Burning Characteristics of Building Materials / Underwriters Laboratories 723 standard (using a Steiner Tunnel) assign asbestos cement board a flame spread and smoke developed rating of 0, and red oak flooring a flame spread and smoke developed rating of 100. In the tunnel, a 20-inch by 25-foot sample of the material to be tested is placed horizontally at the top of the tunnel, and a gas burner is used to ignite one end of the sample. The rate of flame spread toward the other end of the sample and the density of the smoke are measured and compared to the asbestos cement board and red oak standards. Since most EIFS is installed vertically on walls, it behaves differently than in the test tunnel: flame spread on a vertical sample is more rapid than in the tunnel in the laboratory. Visit NFPA 255 for the details on the Steiner Tunnel Test.

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Please note that the Classes A, B, and C assigned by NFPA 101, Life Safety Code, to ranges of flame spread and smoke developed apply only to interior finish materials, and are not related to the fire-resistance ratings (like a 1.5-hour-rated door in a two-hour-rated wall assembly) required by other fire and building codes. However, the EIFS Industry Members Association (EIMA) Web site states that “EIFS alone do not have a fire rating. Testing has been performed to confirm that the fire resistance of an already rated wall assembly is maintained and is not reduced by the addition of an EIFS.”

The EIFS is common on all types of buildings, including “big box” stores, high-rises, commercial buildings, multi-family residences, and single-family dwellings. For more information, internet search “eifs”.

The EIMA Web site publishes the Guide to Exterior Insulation & Finish System Construction, available as a free download (18 pages, 5.01 MB) at

Gregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. He has a bachelor’s degree from St. Norbert College. He has more than 30 years of experience in facilities management and building construction.

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