Tech Today

Do you overspecify?

A large number of project specifications for low-slope membrane roof systems designate an Underwriters Laboratories (UL) Inc. Class A fire-resistance rating and FM Approvals 1-90 wind-resistance approval. For many buildings' roof systems, these classifications are in excess of building codes' minimum requirements.

This month, I will explain how specific fire- and wind-resistance classifications are determined.

External fire resistance

Roof assemblies' resistances to exterior fire exposure are tested and classified using two similar test methods: ASTM E108, "Standard Test Methods for Fire Tests of Roof Coverings," and UL 790, "Tests for Fire Resistance of Roof Covering Materials." These tests provide the basis for the "Class A," "Class B" and "Class C" designations.

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