Concealed Spaces in Mass Timber and Heavy Timber Structures

Concealed spaces, such as those created by a dropped ceiling in a floor/ceiling assembly or by a stud wall assembly, have unique requirements in the International Building Code (IBC) to address the potential of fire spread in non-visible areas of a building. For mass timber building elements, the choice of construction type can have a significant impact on concealed space requirements. This paper outlines the construction types that allow exposed structural mass timber elements—including cross-laminated timber (CLT), glue-laminated timber (glulam), nail-laminated timber (NLT), structural composite lumber (SCL), and tongue-and groove (T&G) decking.