What is a class 1 roof?

What is a class 1 roof?A Class 1 roof designation requires approval from either Factory Mutual Research (FMR) or Underwriters Laboratory (UL). The roof design is tested, and then if it gains approval, must be installed exactly as tested.

Inspection is detailed and exacting. No building material substitutions or assembly technique can vary from the prescribed protocol, not even the thickness or dimensions. Insurance rates and coverage are affected, and building codes may be violated by breaking with installation guidance.

Each substituted component or technique must be approved by UL or FMR.

Confusion occurs when roofs are discussed as A, B, or C and then 1. Class 1 is a more rigorous standard. Class 1 roofs can substitute for A,B, or C; but not all A, B, or C are rated as Class 1.

A, B, and C designations explain the severity of external fire exposure the roof can withstand: A being severe, B moderate, and C light. Class 1 roofs are tested for:

  • Fire
  • Wind uplift
  • Hail
  • Water leakage
  • Foot traffic
  • Corrosion resistance

UL tests wind uplift by exposing roofing assemblies to a two hour sixty plus mile per hour wind. Any lifting, even a single shingle, fails the assembly.

The hail belt through the Midwest has experienced devastating hail storms causing more monetary damage than hurricanes along the east coast. Companies now offer discounts for impact resistant roofing materials in these areas prone to large hail.

Water leakage is generally a function of how the roof layers are attached, and how the roof assembly fixes to the structure. For this reason, assembly protocol is important.

Foot traffic is another impact related hazard: slates break, shingles scuff up and lift, metal bends.

Metal roofs, screws, and nails need to be corrosion resistant to maintain integrity.

UL and FMR design, implement, and monitor test protocols to assure quality standards in roofs. When Building Codes require Class 1 roofing, serious protection and service are expected. This designation is not easily earned.