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CMU Partitions: How Much Reinforcement Is Actually Required?

Words: Block Design Collective
Photos:CMU Checkoff


Walk onto almost any job site and you’ll find masons laying out interior partitions much the same way they did decades ago. The work looks straightforward: stack the units, strike clean joints, and keep the wall plumb. And the function of these partitions hasn’t changed much either. They still divide occupied spaces, help control sound, provide fire protection, and contribute to the regulated indoor environment that building occupants expect.

While the role of these walls remains consistent, the way they are designed and detailed has become more involved. Today’s codes, load requirements, and performance expectations mean that even a simple nonbearing CMU partition comes with unique design considerations.

This overview gives masons and contractors practical awareness of the loads behind partition design, the reinforcement patterns they should expect to see, and the project details worth confirming before work begins.

Why Nonbearing Doesn’t Mean Non-Designed
Nonbearing CMU partitions don’t support gravity loads from floors or roofs, and they aren’t part of the building’s lateral-force-resisting system. Codes even require these walls to be isolated so they don’t unintentionally take on loads they’re not meant to resist.

Still, these walls must be designed to handle several kinds of forces. Understanding what those forces are, and knowing what information should appear in the drawings helps contractors spot issues early and keep the field process efficient.

 

Load Types Influencing Partition Reinforcement

  • Dead Loads: Every wall must support its own weight. This is straightforward but still forms the foundation for the rest of the design.

  • Occupant Live Loads: Most states require interior partitions to be designed for a minimum 5 psf horizontal load. This covers routine use: people leaning on walls, equipment bumping them, or furniture being moved. Contractors should expect to see this noted in the structural design criteria.

  • Wind Loads: Even interior partitions take on internal wind pressure, because buildings are never airtight. Most buildings use 18% of the external wind pressure to define internal loads. For example, a 40 psf external pressure corresponds to an internal pressure of 7.2 psf.

    Contractors don’t calculate this, but it’s helpful to recognize why reinforcement may appear heavier in certain areas, especially in structures with large open bays or overhead doors, which can increase internal pressures to 55% of external wind loads.

  • Earthquake Loads: In moderate and high seismic regions, interior partitions must resist shaking. For Seismic Design Category D and above, codes require at least one No. 4 bar every 48 inches, even when the wall wouldn’t otherwise need that much reinforcement. In low seismic regions, the internal wind pressures will control the design of the partition.
Efficient Reinforcement
Partition walls rarely see the design loads that structural components of a building are designed to resist, which means reinforcement can often be spaced widely without sacrificing performance. Most CMU partitions include joint reinforcement for crack control. Under typical partition-level loads, this joint reinforcement can also serve as the primary structural reinforcement, supported by vertical bars spaced at broad intervals.

This approach provides several benefits for contractors:

  • Less steel to place

  • Simpler installation with fewer congested cells

  • Reduced installation time and costs
And it still meets code while delivering excellent performance.

 

What Reinforcement Spacing To Expect
Design tables developed for 6-inch CMU with joint reinforcement at 16 inches on center show just how efficient partition reinforcement can be:

  • Low and moderate seismic regions: Vertical No. 4 bars are commonly spaced up to 120 inches for many standard partition heights.

  • High seismic regions (SDC D+): Vertical reinforcement must not exceed 48-inch spacing, regardless of calculated demand. This is a code requirement, not a masonry limitation.
.        

Understanding where these numbers come from helps contractors anticipate what materials will be needed on-site and why certain walls require more steel than others.

The efficiency in these designs is realized by combining the load distribution capacity of both the joint reinforcement and vertical No. 4 reinforcing bars. Full methodology is available HERE.

Key Project Information You Should Expect To See
Generally, the design of interior partitions requires knowing two design parameters for wind and seismic loading. If they’re missing, it’s worth requesting clarification early.

  1. Design Wind Speed: This determines the internal wind pressures used in the design.

  2. Seismic Design Parameter (SDS)
    - This defines whether the wall must consider seismic forces and whether prescriptive reinforcement applies.
Most structural notes include these values. If not, the design professional will obtain them using the ASCE Hazard Tool: https://ascehazardtool.org/.

Contractors aren’t responsible for calculating loads, but confirming that this information is shown and consistent helps avoid changes once work begins or provides opportunities for value engineering.



When Unreinforced Partitions Are Still Allowed
In low-wind and low-seismic regions, some interior CMU partitions may be unreinforced. TMS 402 provides tables for allowable spans based on:

  • Partition thickness

  • Mortar type

  • Out-of-plane design load

  • Span-to-thickness ratio
Example: For an 8-inch CMU partition using Type S mortar and designed for a 10 psf load:

  • Span-to-thickness ratio = 18

  • 8-inch thickness × 18 = maximum span of 144 inches, or 12 feet

Source: 2016 TMS 402/602

CMU Makes Partition Work Predictable
Reinforced or unreinforced, CMU partitions deliver:

  • Fire resistance

  • Noise reduction

  • Impact resistance and durability

  • Straight, stable walls

  • Long-term performance with minimal maintenance
CMU partitions give contractors more than structural strength. They deliver fire resistance, sound control, durability, and long-term stability in one system. Choosing CMU whenever possible ensures reliable performance long after construction is complete.

The Block Design Collective offers fast, reliable assistance with CMU design at no cost, from partition reinforcement to complex detailing. If you have questions about code, constructability, or any aspect of masonry design, visit www.blockdesign.org for expert guidance.


About: Technical Talks
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