May 2007

Exterior Walls, Foam Insulating Materials, and Property Risk Considerations

Potential for irony exists when the scales tip from prudent efforts to conserve building energy with insulating materials only to discover they have become a fuel source for hostile fire.

Since the widespread use of plastics in the 1960’s the severe fire hazard inherent with plastics has become well known. As carbon-hydrogen based compounds, Group A plastics, including those used for insulation in the construction industry, have an equivalent pound-for-pound heat release as gasoline when burning. They burn rapidly and also produce acrid smoke laden with toxic gases. Because of the severity of the threat a great deal of attention has been given to reducing the risk exposure of foamed plastics used in construction.

Foamed plastics are used for exterior building insulation by either incorporating them into building construction or being applied to wall/ceiling surfaces as a spray. The three principal compounds most commonly found in foam insulation are expanded or extruded polystyrene, polyurethane, and polyisocyanurate (polyiso).

When foamed plastic insulation is incorporated in exterior building wall construction, it may be in the form of insulated metal clad panels, often referred to as prefabricated sandwich panels; or, as an exterior insulation attached to the outside of an exterior wall substrate. The latter are known as Exterior Insulation and Finishing Systems (EIFS). Spray applied foam insulations are typically used to improve heat and cooling efficiency for older structures and tanks.

Foam plastics used in prefabricated sandwich wall panels include polyurethane, polyiso and polystyrene. The facing material covering the inner foam core may vary. Facing materials include: metal foils, steel sheets or aluminum sheets. There are a variety of methods for cladding the sandwich panel systems together. The companies manufacturing these panels may elect to have their panels tested by various nationally recognized testing agencies to determine the degree of flammability their products possess.

Similar testing may be attained by companies manufacturing EIFS systems and spray applied foam products. The foam insulation of choice for EIFS is polystyrene and for spray applied insulation the foam of choice is polyurethane. Typically, from a property fire protection standpoint, the National Fire Protection Association (NFPA) Standards, FM Global Data Sheets, FM Global Approval Guide, and Underwriters Laboratories (UL) Listing Directories are the recognized property loss prevention guidelines in the United States.

Polystyrene and polyurethane are thermoplastic plastics. These materials soften or melt when heated and harden when cool. They can generally be reheated and reformed. Thermoplastics have a tendency to melt and form burning pools of flammable liquid.

Polyisocyanurate is part of a group of plastics called thermoset plastics. These materials typically form into a permanent shape with heat and pressure applied during a molding process. Polyisocyanurate forms a rigid foam when its constituent compounds are blended. Polyiso, like other thermoset plastics, has a tendency to char when heated.

Regardless of the type or insulating method, foam plastics should be FM Global approved and/or UL listed as fire resistive assemblies or component materials. Prefabricated insulated metal panels used for exterior building walls and EIFS construction are discussed below.

Things to consider when evaluating insulated metal panel sandwich walls for fire exposure

The FM Global recommended facing materials for non-FM Global approved panels should have a minimum thickness of 26 gauge for steel sheet and 0.032 in. for aluminum sheet. There should be no air voids and the facing sheets should come in direct contact with the expanded foam core. The metal joints should overlap ½ in. or more and fastening should be with sheet metal screws with a minimum spacing of 36 in. The metal facing does not act as a thermal barrier, but instead restricts oxygen. It is important that the method of cladding the metal skins and together with the insulation core is such that the metal skins won’t fall away during a fire. This is another argument for full-scale testing, such as the FM Global Corner Test (ANSI FM 4880).

If the prefabricated panels are FM Global approved without sprinklers, then sprinklers are only required based on the hazard of occupancy and contents. Otherwise, FM recommends automatic sprinkler protection be provided based on the occupancy, but no less than with a design density of 0.20 gpm/sq. ft. over 2,000 sq. ft. plus 250 gpm for hose stream allowance for non-approved panels. If the panels are non-FM Global approved without sprinklers in an occupancy not requiring sprinklers, then perimeter sprinklers for the walls are acceptable.

Providing a thermal barrier over sandwich panels and/or spray applied foam insulation that are non-FM Global approved is another recommended solution to attaining a fire resistive wall. Thermal barriers retard the heat flow and prevent oxygen from reaching the foamed plastic. Acceptable thermal barriers may include:

  • Type X Gypsum sheetrock (½ in.)
  • Fire retardant plywood (½ in.)
  • Portland cement plaster on metal lath (½ in.)
  • Masonry units
  • Approved mineral coatings
  • Fire retardant coatings and cellulosics

Fire retardant paint does not qualify for the application as a thermal barrier. It is pointed out that neither metal facing nor thermal barriers are part of the actual properties of an insulation system.

Things to consider when evaluating Exterior Insulation and Finishing Systems (EIFS)

EIFS systems were first developed in Europe during the 1950’s. As the name for the system indicates, it is an insulating system installed on the exterior of buildings. It can be fashioned to look like concrete, stucco, and even brick. Because of this, it can easily be mistaken for substantial non-combustible construction. In fact, in a widely publicized fire in the northeast during the late 1980’s, while battling a blazing building, the fire department was shocked to see the neighboring building 20 ft. away catch fire. They thought it was a concrete building.

EISF systems are installed to exterior building wall substrates during construction. They are not load bearing walls. The method for installation is similar for all companies manufacturing EIFS systems. The typical system assembly is as follows:

Substrate: A substrate is used by incorporating it with the building’s skeletal frame. The skeletal frame may be steel or wood. Wood is discouraged and the steel frame should be designed for wind and structural loads.

Substrates for EIFS systems include:

  • Concrete
  • Masonry Block
  • Gypsum sheathing (water-resistant grade, ½ in. thick minimum should be used)
  • Brick
  • Plywood (discouraged, but approved as fire resistive acceptable)
  • OSB – Oriented Strand Board (discouraged, but approved as fire resistive acceptable)
  • No Substrate, foam board is attached directly to metal or wood stud framing (not recommended)

Insulation Board: Foam polystyrene insulation board is either mechanically attached or adhered with adhesive to the substrate. The thickness of the foam board depends on the thermal resistance to heat flow (R-value) to be achieved in a given region. Thicknesses commonly range from less than 1 in. to 4 in.

When substantial non-combustible substrates are used fuel contribution from the building wall itself to a fire inside the building may be considered negligible. However, external fire exposures, such as neighboring buildings, combustible yard storage, idle pallets, and brush or forestation are high profile a fire risk concerns with EIFS systems; particularly as the foam board increases in thickness. Traditional HPR insurance carriers considered any building having an EIFS system with 3 in. foam board, or more, as a combustible building. Another rule of thumb that was used by some carriers with respect to fire exposure separation and EIFS permitted the following:

Allowable EIFS Foam Board Thickness for Various Severity Exposures within 50 ft.
Exposure Severity
Maximum Foam Board Thickness
No Exposure
< 1 in.
< 1 ½ in.
Moderate to Severe
3 in.

NFPA 80A, “Recommended Practice for Protection of Buildings from Exterior Fire Exposures” and/or FM Global Data Sheet 1-20, “Protection Against Exterior Fire Exposure,” should be consulted for further information.

Reinforcing Mesh: Reinforcing mesh is applied to the substrate mounted foam board using a resin. The resin may be a polymer-based resin for Class PB systems, or it may be a polymer-modified resin for Class PM systems. These resins are also known as base coats or bonding agents. The reinforcing mesh is a woven-treated fiberglass material.

Base Coat: Base “adhesive” coats are typically proprietary formulations derived from acrylic compounds. The base coat resins can be mixed with Portland cement or used as a 100% base coat resin. The reinforcing mesh is either embedded in the base coat or the base coat is applied over the mesh. The base coats should have a uniform thickness with no mesh showing. The thicknesses may vary depending on the manufacturer’s specifications. Nominal thicknesses range from 0.250 in. to 0.375 in.

Surface finish coat: The surface finish coat is sometimes called the facing. It is similar to base coat formulations and is often referred to as a “synthetic stucco.” The finish coat provides texture, color and weather resistance. The thickness for surface finish coats varies as noted above.

FM Global approved EIFS systems should be installed. Automatic sprinkler protection should be provided in the building and the design based on the hazard of the occupancy. Non-combustible, non-wood based substrates and framing should be used. Based on FM Global, it is further recommended that current compliance reports be secured from the manufacturer for the following: National Evaluation Service (US), BOCA Evaluation Services, ICBO Evaluation Services, Public Safety Testing and Evaluation Services that show structural performance, fire performance, durability, and component performance. Full scale fire tests should be used to cite fire performance. Examples of these tests are: FM Global Approvals Corner Test, UBC 26-7 (formerly 17-6), UBC 26-3, UBC 26-9 and CAN/ULC-S134.

If EIFS construction being considered does not meet the foregoing recommendations, Risk Logic can be contacted for further evaluation of EIFS construction for property protection risk exposure.

Overview of Selected Burning Characteristic Test Methods

Overview: “FM Approvals 25 ft. (or 50 ft.) High Corner Test” This is a full scale fire test that can be used to demonstrate building materials in vertical and horizontal orientations that are likely to occur during actual fire conditions. It is often preceded by testing the test material using the smaller scale “FM Global Wall-Ceiling Channel Test” to see if it makes sense to undergo the more expensive full scale test on the material in question. The FM Global Corner Test is intended to test fire propagation and not smoke development. The test can be conducted with and without benefit of sprinkler protection; and may be approved in the FM Global Approval Guide accordingly. In the FM Global 25 ft. High Corner Test walls using the test material are formed to create a corner. One wall is approximately 38 ft. and the other 50 ft. long. The ceiling may be composed of the test material or simply of a non-combustible surface. A single pile of stacked wood known as a wood crib is placed in the corner and ignited. The wood crib is 5 ft. high and weighs approximately 750 lbs. and is intended to represent a fire exposure not severe enough to justify sprinkler protection in a non-combustible building with a non-combustible occupancy. The test outcome is considered successful if no self-propagating flame results and the fire does not burn through the top cladding of the material. FM Global grants a 30 ft. construction height for panel assemblies using foam insulation passing the 25 ft. High Corner Test. Approvals for construction heights over 30 ft. need to satisfy the 50 ft. High Corner Test.

Note: FM Global advises to disregard “individual comparative testing” for all foamed plastics used in construction. Tests of this nature include ASTM E-84 (aka UL 723 and Steiner Tunnel Test).

Overview: ASTM E-84 “Standard Test Method for Surface Burning Characteristics of Building Materials” The results for tested materials using this test method are commonly found in product specification sheets and appear as index ratings for Flame Spread and Smoke Developed. Presumably a flame spread result = 25 is considered non-combustible, and a smoke developed index = 50 is considered acceptable by most Code enforcers and Jurisdictions Having Authority (JHA’s). This is a satisfactory test method for many materials. However, it has been clearly demonstrated that ASTM E-84 does not reflect the burning behavior under actual fire conditions for foam plastic products. While the listing test results found in product specification sheets may indicate a flame spread index less than 25, they may fail to elaborate on the melted pool of burning plastic material below the test apparatus.

It is also advised to disregard tests involving ignition resistance (such as tests using various forms of Radiant Panel Testing) and match-scale testing. Other small scale tests that should be disregarded often boast that a product material is non-burning, self-extinguishing and/or non-combustible. Examples of these test methods are UL 94, “Tests for Flammability of Plastic Materials” and the NFPA 701 “Match Flame Test,” also known as the Ashtray Test of Combustible Materials.

Overview: “Radiant Panel Testing” Radiant Panel Testing is used for flammability testing by several agencies using similar methods. In general the surface of a test material is subjected to a gas-fire radiant heat panel to temperatures ranging from 1,500ºF to 1,800ºF and after 15 minutes to 20 minutes an igniter is used at the material test surface to see if it will sustain a flame 5 seconds or longer.

Overview: UL 94, “Tests for Flammability of Plastic Materials” This small scale test is carried out with a laboratory Bunsen burner and a plastic sample measuring 5 in. long X ½ in. wide X ½ in. thick oriented either horizontally or vertically using ring stand apparatus. The significance of this test appears to be limited to consumer product safety issues and is in no way indicative of burning characteristics of plastic materials used in construction.

The EIFS industry has an industry trade group known as EIFS Industry Members Association (EIMA). EIFS Industry Members Association states on their website 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.” It is interesting to note that EIMA fails to mention details for the referenced testing performed.

Other important considerations for exterior walls with foam insulation include:

Maximum 30 ft. metal sandwich panel height unless tested and approved for a higher distance Maximum foam density of 0.67 lbs/ft2 where polystyrene foam core is used A thermal barrier over foam insulation systems may be recommended where dry pipe sprinkler protection is installed.

Wind hazard design in hurricane prone areas should be evaluated FM Global notes four problems that can be encountered with EIFS:

1. Steel and wood framing can deform or buckle
2. Deflection can cause sheathing and coatings to delaminate
3. Sheathing can pull away from framing and/or substrates
4. A combination of any three of the above may result in permanent damage

Impact hazard resistance from small and large missiles in hurricane prone areas
Resistance to salt water corrosion
Resistance to mildew
Adequate drainage within EIFS systems
EIFS systems should be installed 8 in. above grade and landscaping
FM Global recommends electrical wiring penetrating or embedded in EIFS systems should be metal conduit or the wiring should be Type AC cable, Type MI cable, or Type MC cable
Electric lights embedded in or attached to EIFS walls should be listed for this purpose, and clearances between the fixtures and foam insulation should meet the listing requirements
EIFS sealants and caulking should be inspected every five years and repaired/replaced as needed

Risk Logic Inc. will evaluate any concerns you may have in using foamed plastic insulating materials with respect to property loss exposure for pre-existing construction or new construction projects. If you would like to schedule a survey or consultation meeting, please contact Risk Logic.

1. National Fire Protection Association – NFPA
2. FM Global
3. Industrial Risk Insurers: IRI News/Comments
4. Warnock Hersey
5. Polyisocyanurate Insulation Manufacturers Association – PIMA
6. EIFS Industry Members Association – EIMA