Given: A building of Type IV-B construction is designed to be greater than six stories...

The intended code exception is shafts and vertical exit enclosures , making option B correct. The governing construction-phase provision is 2021 IFC Section 3303.5, which applies to buildings of Types IV-A, IV-B, and IV-C designed to exceed six stories above grade plane.

Where Section 602.4 of the IBC requires noncombustible protection, at least one layer must be installed on building elements located on floor levels—including mezzanines—more than four levels below active mass timber construction before additional floor levels can be erected. The provision is intended to prevent a tall mass timber project from accumulating an excessive number of substantially unprotected combustible stories during erection.

Section 3303.5 expressly states that shafts and vertical exit enclosures are not considered part of the active mass timber construction for application of this construction-progress requirement. Therefore, B is the examination answer.

Mezzanines are expressly included in the protected-level requirement. Required protection for floors, walls, and ceilings under IBC Section 602.4 progresses with construction subject to the IFC provision. The same section also requires standpipes, an approved water supply for fire department operations, and timely installation of required exterior wall coverings.

References/Topics: 2021 IFC Section 3303.5; 2021 IBC Section 602.4; fire safety during construction of tall mass timber buildings.