Impact of Prescriptive Fire Design Provisions on Embodied Carbon for Mass Timber and Hybrid Mass Timber Floors

Abstract

Structural mass timber has been used more often in buildings over the last 5 years, given its potential to be a sustainable alternative. However, concerns still exist around the fire safety of mass timber structures, and current mass timber building designers must consider a variety of fire protection strategies, including but not limited to noncombustible protection and design for sacrificial char thickness. This research focuses on better understanding how prescriptive code fire protection strategies affect the sustainability goals that have partially driven mass timber use. This paper studies how decisions during early design can reduce embodied carbon (EC), the initial energy use of a structure’s construction. Five structural floor system types were modeled parametrically for various levels of fire protection. System types included timber–concrete composites, cross-laminated timber (CLT)–steel hybrids, and all-timber systems. The resulting EC data analysis reveals that all-timber systems perform the best for EC when the fully protected option is used at shorter spans, when the combined approach option is used at midrange spans, and when the fully exposed timber option is used at longer spans. Across all studied systems, the shallowest possible depth occurred for the 10-ft (3.05-m) spanning CLT–steel hybrid systems at 11.5 in. (292 mm) deep for the fully protected system, and the lowest possible EC was 10.5 lb CO2 eq/ft2 (51.3 kg CO2 eq/m2) for the fully protected 10-ft (3.05 m) all-timber system.