Roof Classes

Roofing systems are often specified according to the “Class” of roof required. The class source or classifying authority, however, is frequently unidentified or omitted. Agencies governing the classification roof assemblies and components include the following:

1 Underwriters Laboratories of Canada (ULC)

Underwriters Laboratories of Canada (ULC) test and classify roof assemblies (includes roof deck, vapour retarder, insulation, membrane, etc.), roof components, and (specifically) roof-covering materials according to their fire resistance and fire hazard characteristics. Roof assemblies are evaluated for their performance when exposed to fire from an internal source (i.e. directed onto the underside of the roof deck) and roof-covering materials (membranes) are evaluated according to their performance when exposed to fire from an external source. Usually the roofing specification is concerned with the different classification of roof-covering materials, as follows:

• Class A includes roof coverings which are effective against severe fire exposures. Under such exposures, roof coverings of this class are not readily flammable and do not carry or communicate fire; they afford a fairly high degree of fire protection to the roof deck; they do not slip from position; they possess no flying brand hazard; and they do not require frequent repairs in order to maintain their fire resisting properties.

• Class B includes roof coverings which are effective against moderate fire exposures. Under such exposures, roof coverings of this class are not readily flammable and do not readily carry or communicate fire; they afford a moderate degree of fire protection to the roof deck; they do not slip from position; they possess no flying brand hazard; and they may require infrequent repairs in order to maintain their fire-resisting properties.

• Class C includes roof coverings which are effective against light fire exposures. Under such exposures, roof coverings of this class are not readily flammable and do not readily slip from position; they possess no flying brand hazard; and they may require occasional repairs or renewals in order to maintain their fire-resisting properties.

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2 Underwriters Laboratories, Inc. (UL)

Although UL jurisdiction is limited to the United States, some materials sold in Canada have UL test results only. UL evaluates and describes the performance of roof assemblies and components when exposed to internal and external sources of fire, similar to ULC. Roof covering materials are also classified into Class A, Class B, or Class C. In addition, UL classifies materials according to their resistance to wind uplift. Materials in this category are rated as Class 30, Class 60, or Class 90 materials.

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3 Factory Mutual (FM)

Factory Mutual (FM) evaluates the fire resistance , the wind uplift resistance, and other properties of a roof assembly for the purposes of building insurance. The FM Approved assembly must contain listed components only.

Classifications are as follows:

• Class I Fire
• Class II Fire
• Class 1-60
• Class 1-90

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4 Canadian General Standards Board (CGSB)

Canadian General Standards Board (CGSB) classifies prepared membranes as follows:

• CGSB 37-GP-52M: classifies “Roofing and Waterproofing Membrane, Sheet Applied, Elastomeric” (most commonly EPDM) according to end use, as either:
  • Class A - Exposed
  • Class B - Non-Exposed
• CGSB 37-GP-54M: classifies “Roofing and Waterproofing Membrane, Sheet Applied, Flexible, Polyvinyl Chloride” according to end use, as either:
  • Class A - Non-Exposed
  • Class B - Exposed
  • Class C - Waterproofing
  • Class D - Asphalt Compatible Flashing Material
• CGSB 37-GP-56M: classifies “Membrane, Modified, Bituminous, Prefabricated and Reinforced for Roofing” according to finished membrane surface, as either:
  • Class A - Granule Surfaced
  • Class B - Metallic Surfaced
  • Class C - Plain Surfaced

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5 Canadian Roofing Contractors Association (CRCA)

The 1978 Roofing Specification manual classified a Class A roof as a 4-ply built-up roof membrane (organic felt), and a Class B specification meant that one ply and one mopping of asphalt was deducted (3-ply built-up roof). The current CRCA Roofing Specification manual no longer refers to Roof Classes. This classification system should be considered obsolete.

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