TL;DR — Key Takeaways
• IBC Chapter 21 adopts TMS 402/602 (Building Code Requirements and Specification for Masonry Structures) as the primary masonry design and construction standard.
• TMS 402-22 is the edition referenced by IBC 2024. The "402" covers design; the "602" (published together) covers construction specifications.
• Three masonry design methods are recognized: strength design (§2101.2.1), allowable stress design (§2101.2.2), and empirical design (§2109 — limited applications only).
• Empirical design (no engineering calculations) is only permitted for SDC A and B, for limited building heights, and for specific construction types — it is not available for most commercial buildings.
• Seismic requirements escalate significantly from SDC A through F — at SDC D and higher, all masonry in the seismic-force-resisting system must be specially reinforced and detailed (special reinforced masonry shear walls).
• Special inspections per §1705.4 are required for all masonry in SDC C and above, and for structural masonry in SDC A and B.
• Grout requirements: Masonry cells must be grouted in a specific sequence; ASTM C476 governs grout mix design; minimum grout strength is typically 2,000 psi at 28 days.
• Lintel design for openings in masonry walls must be designed per TMS 402 using structural analysis or pre-engineered lintel tables.
The IBC-TMS 402 Framework
IBC §2101.2 adopts TMS 402 by reference: "Masonry structures and components thereof shall be designed and constructed in accordance with TMS 402/602."
TMS 402 (The Masonry Society's Building Code Requirements for Masonry Structures) is the masonry equivalent of ACI 318 for concrete — the comprehensive design and construction standard. IBC Chapter 21 supplements TMS 402 with additional provisions and modifications, particularly for seismic design.
Key materials covered:
• CMU (Concrete Masonry Units): ASTM C90 — most common structural masonry in the U.S.
• Clay brick: ASTM C216 (facing brick), C652 (hollow brick)
• Concrete brick: ASTM C55
• Mortar: ASTM C270 — Types S, N, and M for different structural applications
• Grout: ASTM C476 — fine and coarse grout for filling cells
Masonry Design Methods
Strength Design (§2101.2.1)
Strength design applies factored loads (1.2D + 1.6L, etc.) and compares them against the design strength of the masonry assemblage. This is the preferred method for structural masonry in SDC C and higher and for any masonry in the seismic-force-resisting system.
Strength design requires knowledge of the specified compressive strength of masonry (f'm) — typically 1,500 to 3,000 psi for CMU masonry — and the grout strength.
Allowable Stress Design (§2101.2.2)
ASD applies service-level loads against allowable stresses derived from the masonry assembly test strength. ASD has a long track record in masonry design and is still widely used. TMS 402 provides allowable stress tables for flexure, shear, and axial loads.
Empirical Design (§2109)
Empirical masonry design — sizing walls based on height-to-thickness ratios without structural calculations — is only permitted for:
• SDC A and B buildings
• Buildings not exceeding 35 feet in height (3 stories)
• Specific occupancy limitations
Most commercial projects cannot use empirical design. It is occasionally used for small residential or agricultural buildings in low seismic zones.
Seismic Requirements for Masonry (§2106)
Masonry seismic requirements escalate with SDC:
| SDC | Minimum Masonry System |
|---|---|
| A | Unreinforced masonry permitted (§2106.1) |
| B | Unreinforced masonry permitted with additional minimum reinforcement |
| C | Intermediate reinforced masonry walls; minimum vertical and horizontal reinforcing |
| D, E, F | Special reinforced masonry shear walls required; minimum reinforcement ratios; wall segments must meet boundary element requirements |
Special Reinforced Masonry Shear Walls (SDC D–F):
• Minimum vertical reinforcement: #4 bars at 48-inch centers
• Minimum horizontal reinforcement: #4 bars at 48-inch centers (or bond beam at 16-inch maximum spacing)
• All cells containing vertical bars must be grouted solid
• Shear reinforcement must be provided at every floor and roof level
• Grout must achieve minimum f'c = 2,000 psi
CMU Wall Construction Requirements
Unit Dimensions and Specifications
Standard CMU (Concrete Masonry Unit):
• Nominal dimensions: 8" × 8" × 16" (actual: 7-5/8" × 7-5/8" × 15-5/8" — 3/8" mortar joint)
• Other common nominal heights: 4", 6", 12"
• ASTM C90 Grade N-I: used for above-grade and below-grade construction
• ASTM C90 Grade N-II: above-grade only
Mortar Types
| Mortar Type | Compressive Strength | Common Use |
|---|---|---|
| Type S | 1,800 psi (28-day) | Below grade, retaining walls, exterior walls |
| Type N | 750 psi | Interior non-load-bearing walls, above-grade exterior (mild exposure) |
| Type M | 2,500 psi | High-load-bearing or below-grade in severe conditions |
Type S is the most common structural mortar for CMU construction.
Grouting Requirements
Cells containing vertical reinforcement must be grouted solid. In SDC C and higher, additional cells may be required to be grouted per the reinforcing schedule. Grout placement must follow TMS 602 procedures:
• Lift height not to exceed 5 feet without cleanouts
• Cleanouts required at the base of walls ≥5 feet tall unless grout is placed in lifts of ≤ 5 feet
• Consolidation (mechanical vibration or rodding) required for all grout placements
Lintels
Lintels over openings may be:
• Reinforced masonry bond beam lintels (most common — reinforced CMU unit with grouted reinforcing)
• Precast concrete lintels
• Steel angle lintels (for light cladding loads only — not for structural masonry above)
Lintel design must account for the tributary load from masonry above the opening, any concentrated loads from floor or roof beams bearing on the wall adjacent to the opening, and the required bearing length on each side of the opening.
Special Inspections for Masonry (§1705.4)
For masonry in SDC C and higher, IBC §1705.4 requires continuous special inspection during:
• Placement of masonry units
• Grouting operations
• Placement and splicing of reinforcement
For SDC A and B, periodic inspection is required for structural masonry (load-bearing walls). The special inspector verifies mortar mix, unit placement, cell grouting, and reinforcing as specified in the project's Statement of Special Inspections.
Research Masonry Requirements for Your Project
TMS 402 masonry design requirements, seismic detailing, and grout specifications depend on your SDC, occupancy, and jurisdiction. Melt Code lets you search IBC Chapter 21, TMS 402 provisions, and your jurisdiction's amendments together.
Frequently Asked Questions
IBC §2101.2 adopts TMS 402 by reference — TMS 402 is the primary standard. IBC Chapter 21 provides supplemental and modification provisions. The designer applies TMS 402 as the base document and checks IBC §2101–§2109 for modifications.
California is predominantly SDC D. Unreinforced masonry (URM) is not permitted for the lateral-force-resisting system in SDC C and higher. Existing URM buildings are a significant seismic vulnerability — California has extensive URM retrofit programs. New construction in California requires specially reinforced masonry shear walls per IBC §2106.
Type S (1,800 psi) is a high-strength mortar used for structural applications — below-grade walls, retaining structures, and exterior bearing walls. Type N (750 psi) is a medium-strength mortar used for above-grade non-load-bearing partitions and architectural masonry veneers. Type S or M is required for structural load-bearing CMU walls.
TMS 602 and the project's special inspection program define the testing frequency. A typical commercial masonry project tests mortar by preparing ASTM C270 flow tests and mortar cubes (ASTM C780) at least once per day of masonry work and when proportions or materials change.
References
1. International Code Council — IBC 2024, Chapter 21: Masonry
https://codes.iccsafe.org/content/IBC2024P1/chapter-21-masonry
2. The Masonry Society — TMS 402/602-22: Building Code Requirements and Specification for Masonry Structures
https://www.masonrysociety.org/resources/codes-standards/
3. ASTM — C90: Standard Specification for Loadbearing Concrete Masonry Units
https://www.astm.org/c0090-16a.html
4. ASTM — C270: Standard Specification for Mortar for Unit Masonry
https://www.astm.org/c0270-19a.html
5. UpCodes — IBC 2024 Chapter 21 (searchable text)
https://up.codes/viewer/california/ibc-2024/chapter/21/masonry