Back to Basics - What is the T-Rating

The T-Rating is the duration that a firestop system will resist an increase in temperature on the unexposed side of wall or floor of 325F above its starting ambient temperature, a simple measure of thermal conductivity. T-Ratings are an often-overlooked requirement in building codes requiring contractors and building owners to apply supplemental insulating materials on penetrants or increase spacing between penetrations and construction joints to ensure compliance with the intent of local building codes. 

T Ratings are defined within ASTM E814 (UL1479) (penetration firestop systems), ASTM E2307 (perimeter fire containment systems), and ASTM E2837 (continuity head-of-wall joint systems).

The T Rating may not always equal the F Rating because metal penetrants in firestop systems may get hot, a metal roof deck may not have enough thermal mass to resist temperature rise on the unexposed surface, or a curtain wall may have a metal framing member that passes through the void area at edge of slab. The US codes prescribe situations where T Ratings for penetrants are not required such as penetrants contained in wall cavities, connected to a floor or shower drain above a ceiling membrane, or conduit connecting to switch gear. The US codes do not require T Ratings for continuity head-of-wall joints, such as the intersection of a fire-rated wall and non-fire-rated roof deck or a perimeter fire containment system installed at the edge of slab. 

By STI Engineering Services