December 1, 2006 by Larry Watson, Director of Loss Control, ING Canada
It is estimated that 30% of all commercial buildings constructed in Canada use E.I.F.S. (Exterior Insulation and Finish System). Some insurers are classifying E.I.F.S as a non-combustible construction for rating purposes while others are treating it as combustible.
While buildings in Canada must comply with codes and regulations with respect to life safety, that does not mean structures will be unaffected by heat, smoke and flame. The fire rate should reflect this fact.
Insurers are encouraged to examine their underwriting positions and work with loss control to ensure that buildings constructed with E.I.F.S. are identified and rated against the peril of fire on a consistent basis.
EVOLUTION OF E.I.F.S.
Construction systems and techniques have evolved to meet the demands of a changing world. The use of plastics in building construction has caused concern among insurers because of the undesirable burning characteristics associated with them. Builders use plastics because they are inexpensive, hygienic, lightweight and energy-efficient. But underwriting issues have developed because of the contribution of plastics to fire.
Treating plastics with fire retardants or barriers may improve their behaviour when exposed to fire, but ultimately they are all combustible. Insurers and authorities having jurisdiction actively recommend the use of approved thermal barriers to protect exposed plastics against the adverse effects of fire.
E.I.F.S. (also referred to as EEFISS) is a multi-layered exterior wall system that was developed in Europe in the 1950s and introduced to North America in the 1970s. Simply described, it is an application of expanded polystyrene board stock and polymeric render over a substrate. Its popularity in modern construction is based on its cost, cosmetic appeal, energy efficiency and the ease with which it can be installed.
E.I.F.S. is used in exterior wall construction. It is either field-installed or mounted in panel form directly onto masonry walls or in between vertical structural members of buildings. This is how it works:
Assume structural steel is erected at the site of a new building during the early stages of construction. The steel would appear as columns supporting a non-combustible steel or metal deck roof. The spaces between the vertical structural steel columns are in-filled with steel studs. These steel studs would be installed parallel to the vertical columns of supporting steel. At least one steel girt spanning the structural steel columns horizontally will also be installed. In some cases steel cross members will be placed between the steel columns.
A substrate of drywall, cement board or, in rare instances, treated plywood will be mechanically fastened to the metal studs and girt. The substrate acts as sheathing around the perimeter of the building. Treated plywood is more rigid than drywall, but plywood isn’t used because it is more expensive; in most cases, its use is restricted to decorative parapets or ornamental assemblies on the exterior of the building.
The use of a moisture barrier may be necessary in cases where moisture-sensitive sheathing is used. E.I.F.S. manufacturers and suppliers have developed systems that manage the intrusion of moisture that has penetrated the wall system.
The exterior face of the substrate is clad with expanded polystyrene (EPS) to provide insulation to the structure. EPS is most commonly used, but mineral wool, polyisocyanurate, and polyurethane rigid foam are also options. EPS sheets are either mechanically fastened or glued onto the substrate.
Metal or polymer-coated, fibreglass mesh – selected on the basis of its tensile strength – is adhered to the face of the EPS insulation. Manufacturers of E.I.F.S. will recommend the type of polymer-based adhesive and base coat that should be used to incorporate the supportive fibreglass mesh onto the surface of the EPS. Basecoats can be either combustible or non-combustible and the criteria for fire-testing wall systems in laboratories is based on this fact.
An acrylic polymer finishing system is applied to the exterior of the building over the fibreglass mesh and basecoat. Finishing systems are comprised of roughly textured acrylic binders surmounted by finishing topcoats. Finishing topcoats can be tinted to add colour to the exterior of the building. True stucco is not used because it is less durable and tends to shrink and crack, requiring constant vigilance from property owners.
The interior face of the E.I.F.S. will often be insulated with fibreglass insulation that is clad with drywall.
E.I.F.S. is developed by manufacturers as a complete system and should be installed as such by contractors. E.I.F.S. is subjected to fire tests as a complete assembly using the components that are listed by the manufacturer.
IS E.I.F.S. COMBUSTIBLE?
Should insurers classify E.I.F.S. as non-combustible or combustible?
Insurers classify buildings for rating purposes as being either fire resistive, masonry non-combustible, non-combustible, masonry, masonry veneer, and frame. Basic building construction terminology defines non-combustible construction as being comprised of “materials that do not add fuel to a fire.” Conversely, the term combustible construction defines buildings that are comprised of “materials that do add fuel to a fire.”
As indicated above, there is one major component of E.I.F.S. in which a combustible material is always present – the expanded polystyrene (EPS) insulation. A second potential source of fire could be the basecoat used to incorporate the fibreglass mesh onto the face of the EPS.
When considering the combustibility of a wall, insurers should be concerned with fire propagation from both inside and outside of the wall. The use of combustible EPS raises concerns in both cases. These concerns are diminished when considering E.I.F.S. from the inside, because fire must pass through an interior finish of drywall and drywall substrate before reaching the EPS and breaking the confines of the exterior walls. Of greater concern is that only an acrylic polymer finishing system (with no fire rating) and the base coat stand between the EPS and an external fire source.
When manufacturers submit E.I.F.S. for testing by recognized testing laboratories, the wall system is subjected to heat and flame from the exterior for a period of 15 minutes. Wall systems passing this test do not allow the penetration of fire to the interior of the building for the entire 15-minute test period. But the acrylic polymer does not act as a thermal barrier and therefore the propagation of heat and flame impinging on the exterior of the building rapidly consumes the EPS in the wall system. EPS is a very light material; its composition can cause it to be consumed so quickly, there is hardly enough time for it to significantly contribute fuel to the test fire. Nevertheless, the resulting damage can require insurers to pay a claim on a structure that was underwritten as ‘non-combustible.’ In reality, the structure contained combustible elements that were not reflected in the fire rate.
The presence of combustible EPS insulation in both tested and untested systems – in addition to the use of a combustible base coat – invalidates E.I.F.S. as a non-combustible construction, regardless of what substrate is used (i.e. whether wood or drywall).
It is recommended insurers classify E.I.F.S. as combustible for rating purposes.
The exception would be when E.I.F.S. is applied to the exterior of a non-combustible wall with a fire resistive rating (i.e. a masonry wall). In this case, the wall should retain its non-combustible or fire-resistive status for rating purposes. If a non-combustible insulation such as mineral wool is used in place of EPS, the wall should be classified as non-combustible for rating purposes.
Many E.I.F.S. assemblies have been tested for their ability to resist fire, but some systems have n
ot been. In most cases, the two systems are indistinguishable upon inspection in the field. It is recommended that only fire-tested and approved E.I.F.S. be used in building construction to ensure that the complete wall system meets minimum testing standards.