The inquiry
Required joints—but not a universal spacing rule.
A masonry professional requested guidance on locating control joints in a 4-inch CMU wall constructed over a 6-inch CMU knee wall. The project architect cited a 1.5-to-1 length-to-height ratio, which appeared to require control joints approximately every 6 feet.
The questionDoes TMS 402/602 provide direction for placing control joints in this condition, or should the project use the empirical NCMA guidance?
The expert answer
Control joints are required in concrete masonry work, but TMS 402/602 does not address their specific location and design. The National Concrete Masonry Association technical guidance is the applicable resource for that information.
Proper location and installation are important for several reasons, and there are two principal ways to determine the joint locations:
- Engineering analysis that determines joint size and spacing from CMU shrinkage coefficients and other material and project conditions.
- The empirical method described in NCMA TEK 10-2D, including the maximum length-to-height ratio and maximum recommended spacing in Table 1.
The engineered approach
An engineer can determine control-joint size and spacing using the coefficient of shrinkage and other characteristics of the concrete masonry units and wall system. This design approach is the responsibility of the project engineer.
The empirical approach
The alternate method is the empirical procedure described in NCMA TEK 10-2D. Table 1 uses a maximum panel length-to-height ratio of 1.5 and recommends a maximum spacing of 25 feet. For walls shorter than approximately 16 feet in height, the 25-foot maximum controls.
If the project designer does not locate the joints, Jerry Painter recommended spacing them approximately 22 to 24 feet apart in accordance with Table 1 rather than placing them every 6 feet solely because of the short wall height.
Account for concrete masonry veneer
Because the project involved a 4-inch CMU veneer, the response also identified NCMA TEK 10-4, Concrete Masonry Veneers, as an additional technical resource for the designer and project engineer.
The original inquiry was supported with both TEK Notes so the design team could review the empirical control-joint guidance together with recommendations specific to concrete masonry veneer.
Key takeaways
TMS 402/602 requires control joints in concrete masonry work but does not establish their location and design.
Engineered control-joint design is the responsibility of the project engineer.
The empirical method in NCMA TEK 10-2D uses a maximum panel length-to-height ratio of 1.5 and a maximum recommended spacing of 25 feet.
When the designer has not located the joints, the expert recommended spacing them approximately 22 to 24 feet apart in this condition.
NCMA TEK 10-4 provides additional guidance applicable to concrete masonry veneer.
Florida Masonry Note
Control-joint spacing should be shown clearly in the construction documents. When conditions fall outside the assumptions of an empirical method—or when project geometry, reinforcement, restraint, openings, or material properties require additional consideration—the project engineer should establish the joint design.