FM 4470

FM 4470 is an approval standard published by FM Approvals, the product certification arm of the commercial property insurer FM. Its full title describes single-ply, polymer-modified bitumen sheet, built-up roof (BUR) and liquid-applied roof assemblies for use in Class 1 and noncombustible roof deck construction. The current edition listed by standards databases is dated April 2022.

Products that meet it can be described as FM Approved and are listed in FM's RoofNav database.

What it evaluates

FM 4470 looks at the whole roof assembly, from the structural deck and its attachment up to the weather surface, rather than at one product in isolation. Hazards it addresses include:

• fire from above the deck (external fire) and from below (interior fire spread)
• simulated wind uplift, using methods aligned with ANSI/FM 4474
• susceptibility to hail damage
• water leakage
• foot traffic
• corrosion of metal components
• susceptibility to heat damage

Optional evaluations include puncture resistance, solar reflectance and a noncombustible-core rating for insulation.

Ratings

An FM-approved assembly carries a designation such as Class 1-90. "Class 1" indicates it met FM's fire requirements for interior fire spread and external fire, and the number is the wind uplift rating in psf (here 90 psf, about 4.3 kPa). Hail performance is shown as Moderate Hail (MH) or Severe Hail (SH) where tested.

Who uses it

FM-insured commercial and industrial buildings are often required to use FM-approved roof assemblies installed according to FM Property Loss Prevention Data Sheets. Outside FM's own clients, many specifiers worldwide use FM 4470 approvals as a benchmark for commercial low-slope roofs, and FM test data is accepted in some building code compliance routes in the United States.

Related FM standards

FM Approvals publishes other roofing standards, including 4473 for impact resistance of rigid roofing and 4475 for roof components used in hail-prone areas.