Whether striving to increase interior floor space, searching for the lowest cost solution, minimizing embodied carbon, reducing maintenance efforts in high traffic environments, or weighing all these considerations, interior partition walls constructed of concrete masonry offer an array of benefits. Often overlooked as a solution for interior partitions includes leveraging 6 in. CMU partitions. The Block Design Collective has a comprehensive series of resources covering the design, detailing, and construction of concrete masonry partition walls, including design guides, standardized schedules and details, and design calculators [Ref. 1, 2].
1. COST AND CARBON
There are several variables that directly impact masonry’s installation productivity and thereby its cost to construct – not the least of which is the lay rate for installing masonry units. While it isn’t the only factor that affects construction productivity, the weight of each masonry unit is a key driver behind installation productivity, with 6 in. CMU weighing an average of 5-10 pounds per unit less than similar 8 in. CMU. This translates to an increase in productivity of 15-20% with corresponding cost savings [Ref. 3].
Concrete masonry partitions constructed using 6 in. CMU also offer considerable material savings, which directly translate to reductions in embodied carbon as illustrated in the comparative wall assemblies and grouting schedules shown in Table 1.
2. FIRE RESISTANCE AND SOUND TRANSMISSION CLASS (STC)
The fire resistance rating of a concrete masonry assembly is a function of the volume of masonry units used in the construction of the assembly and the type of aggregate used in the manufacture of the CMU [Ref. 5]. All hollow 6 in. CMU assemblies will have a fire resistance rating exceeding 1 hour. When solid grouted or filled with loose fill materials such as perlite or sand, all 6 in. CMU assemblies will have a fire resistance rating exceeding 3 hours, with some lightweight unit assemblies achieving a 4 hour fire resistance rating.
The Sound Transmission Class (STC) rating of 6 in. CMU partitions is a function of the installed weight of the assembly, which depends on the density of the units and the quantity of grout placed in the assembly. Concrete masonry partitions constructed using 6 in. CMU partitions have STC ratings ranging from the mid-40s for lightweight, ungrouted assemblies to the mid-50s for normal weight, fully grouted assemblies [Ref. 6].
3. CONNECTION DETAILING
Due to the relatively small design loads nonloadbearing partitions must be capable of resisting, it often is not necessary to detail a fully developed anchor at the base of the wall. A more practical connection would be to epoxy-set any vertical reinforcement in the assembly into the supporting slab below. This avoids necessary trade coordination and potential misalignment of the dowels.
Similarly, top-of-wall anchors are available that facilitate the installation of the assembly and any vertical reinforcement present, even with the floor or roof above is already in place, alleviating the need for complicated anchoring systems to support the assembly.
