CBC · California Building Code

Masonry chimneys: footing dimensions, vertical/horizontal reinforcement and seismic anchorage

For homeowners: the CBC requires masonry chimneys sit on 12‑inch thick footings that extend 6 inches past the wall; chimneys in seismic areas must have vertical No.4 bars and 1/4‑inch ties at 18‑inch spacing, with steel straps embedded and bolted to joists to keep the chimney attached to the house.

Ask a question free See coverage

Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

Masonry chimneys must sit on concrete or solid‑masonry footings that are at least 12 in. thick, extend at least 6 in. beyond the face of the foundation on all sides, and be founded below frost depth (or 12 in. below finished grade where frost is not a concern) per § 2113.2. Seismic reinforcement and anchorage requirements depend on Seismic Design Category: SDC A/B do not require seismic reinforcement; SDC C/D require the reinforcement and anchorage specified in § 2113.3 (and its subsections) and § 2113.4; SDC E/F require the reinforcement provisions of §§ 2101–2108 and anchorage per § 2113.4. Vertical reinforcement is specified as No. 4 continuous bars (minimum counts based on chimney width) and horizontal reinforcement (ties) is prescribed in size and spacing; seismic anchors are strap‑type with defined embedment and fastener requirements (see §§ 2113.2–2113.4).

Requirements in detail

Footings and foundations (what to build)

  • Minimum thickness: 12 inches.
  • Minimum projection beyond face of foundation or support wall: 6 inches on all sides.
  • Support: founded on natural undisturbed earth or engineered fill below frost depth; in non‑freezing areas footing must be at least 12 inches below finished grade. See § 2113.2.

Seismic reinforcement — when required

  • Seismic reinforcement is not required for structures assigned to Seismic Design Category A or B.
  • For SDC C or D: chimneys must be reinforced and anchored in accordance with §§ 2113.3.1, 2113.3.2 and 2113.4.
  • For SDC E or F: reinforcement must follow §§ 2101–2108 and anchorage per § 2113.4. See § 2113.3.

Vertical reinforcement (how many bars, placement, grout)

  • Base requirement for chimney widths up to 40 in. (1016 mm): four No. 4 continuous vertical bars anchored in the foundation.
  • Placement: in the concrete between wythes of solid masonry or within cells of hollow unit masonry and grouted in accordance with the referenced grout requirement.
  • For each additional 40 in. (1016 mm) in width or fraction thereof beyond 40 in., provide two additional No. 4 vertical bars. Grout must be prevented from bonding to the flue liner so the liner can expand thermally. See § 2113.3.1.

Horizontal reinforcement (ties / lateral ties)

  • Vertical reinforcement shall be enclosed within 1/4‑inch (6.4 mm) ties (or other reinforcement with equivalent net cross‑sectional area).
  • Spacing: ties (or horizontal reinforcement placed in bed joints) shall be placed at not less than every 18 inches (457 mm) of vertical height (i.e., spacing shall not exceed 18 in. o.c.).
  • At each bend in a vertical bar, provide two such ties. See § 2113.3.2.

Seismic anchorage (strap anchors & fastening)

  • Anchors required at each floor, ceiling or roof line that is more than 6 feet (1829 mm) above grade.
  • Anchor type: two 3/16‑inch by 1‑inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney.
  • Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend.
  • Fastening: each strap shall be fastened to not less than four floor joists with two 1/2‑inch (12.7 mm) bolts. See § 2113.4.

Decision‑relevant dimensions & values (quick reference table)

Item Value / Requirement Code reference
Footing thickness ≥ 12 in. (305 mm) § 2113.2
Footing projection beyond face ≥ 6 in. (152 mm) each side § 2113.2
Footing depth in non‑freezing areas ≥ 12 in. (305 mm) below finished grade § 2113.2
Vertical bars (base) Four No. 4 continuous bars for chimney ≤ 40 in. wide § 2113.3.1
Additional vertical bars +2 No. 4 for each additional 40 in. (or fraction) of width § 2113.3.1
Horizontal ties size 1/4 in. (6.4 mm) ties (or equivalent) § 2113.3.2
Horizontal tie spacing ≤ 18 in. (457 mm) vertically § 2113.3.2
Ties at bar bends Two ties at each bend in vertical bars § 2113.3.2
Seismic anchor strap Two 3/16" × 1" (4.8 × 25 mm) straps § 2113.4
Strap embedment ≥ 12 in. (305 mm) into chimney § 2113.4
Strap extension beyond bend 6 in. (152 mm) § 2113.4
Strap fastening Each strap fastened to ≥ 4 floor joists with two 1/2" bolts § 2113.4
Where seismic reinforcement not required SDC A or B § 2113.3

Exceptions & special cases

  • No seismic reinforcement is required in structures assigned to Seismic Design Category A or B (§ 2113.3).
  • Where the masonry fireplace is constructed completely within the exterior walls, the seismic anchorage requirement is excepted (§ 2113.4, Exception).
  • For structures in SDC E or F, the code refers to the broader reinforced masonry provisions in §§ 2101–2108 for reinforcement design, while anchorage still follows § 2113.4. Do not attempt to apply the simplified § 2113.3.1 rules for SDC E/F — follow §§ 2101–2108 instead.

If your project has nonstandard geometry, unusual loads, or is in SDC E/F, the short prescriptive rules in § 2113.3.1 are not the controlling design path — the code points to full reinforced masonry design in §§ 2101–2108.

Common mistakes

  • Assuming the flue liner will be bonded to the grout — the code requires grout be prevented from bonding to the flue liner so the liner can move with thermal expansion (§ 2113.3.1). Failing to accommodate that causes cracking and liner damage.
  • Under‑counting vertical bars: for any width >40 in., remember to add two No. 4 bars for each additional 40 in. (or fraction thereof) (§ 2113.3.1).
  • Placing horizontal ties too far apart — they must be every 18 in. max; using wider spacing (e.g., 24 in.) for chimneys will not meet § 2113.3.2.
  • Improper anchor embedment or fastening — straps must be embedded ≥12 in. and hooked around outer bars, extend 6 in. beyond the bend, and be fastened to not less than four joists with two 1/2‑in. bolts (§ 2113.4). Substituting smaller straps, shallower embedment, or fewer joists contravenes the code.
  • Applying the SDC C/D prescriptive rules in SDC E/F situations — SDC E/F calls for the full reinforced masonry requirements in §§ 2101–2108 (§ 2113.3).

Worked example — concrete scenario

Scenario: A masonry chimney 60 in. wide, 20 ft (240 in.) tall, located on a house in Seismic Design Category C (so seismic reinforcement and anchorage apply).

  1. Footing:

    • Provide a concrete footing 12 in. thick that extends 6 in. beyond the chimney foundation on all sides, founded on undisturbed soil or engineered fill below frost depth (or 12 in. below finished grade where no frost). (§ 2113.2)

  2. Vertical reinforcement:

    • Base requirement for ≤40 in. width = four No. 4 continuous vertical bars anchored into the footing.
    • Chimney is 60 in. wide: that is 40 in. + fraction (20 in.), so add two No. 4 bars for the fraction of the next 40 in. → total vertical bars = 4 + 2 = 6 No. 4 continuous bars, placed in wythes/concrete cells and grouted as required. (§ 2113.3.1)

  3. Horizontal ties:

    • Provide 1/4‑inch ties (or equivalent) spaced not more than 18 in. vertically. For a 20 ft (240 in.) high chimney: 240 in. ÷ 18 in. = 13.33 → provide ties at 14 levels (i.e., ties at ~0, 18, 36, … up to the top) so that spacing does not exceed 18 in. Two ties must be placed at each bend in the vertical bars. (§ 2113.3.2)

  4. Seismic anchorage:

    • Anchor the chimney at each floor/ceiling/roof line that is more than 6 ft above grade. If the chimney penetrates one floor/ceiling and the roof line above grade exceeds 6 ft, provide anchors at those locations.
    • Use two 3/16" × 1" straps embedded at least 12 in. into the chimney, hooked around the outer vertical bars and extending 6 in. beyond the bend. Fasten each strap to not less than four floor joists using two 1/2" bolts as required. (§ 2113.4)

This example follows the prescriptive path in §§ 2113.2–2113.4 for SDC C. If the site were SDC E or F, the designer must use §§ 2101–2108 for reinforcement design instead.

Related provisions

  • § 2101 through § 2108 — reinforced masonry design provisions referenced for SDC E/F reinforcement.
  • § 2103.3 — grout requirements referenced where vertical bars are to be grouted.
  • § 2111 — masonry fireplace reinforcement and anchorage rules (parallel provisions for fireplaces).
  • § 2113.5 — corbeling limits for chimneys.
  • § 2113.8 — prohibition on chimneys supporting other loads unless designed.
  • § 2113.9 — chimney termination height requirements.

Code references

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

  • CBC § 2113.2 High relevance — show source text

    2113.2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.

    2113.3 Seismic reinforcement. In structures assigned to Seismic Design Category A or B, seismic reinforcement is not required. In structures assigned to Seismic Design Category C or D, masonry chimneys shall be reinforced and anchored in accordance with Sections 2113.3.1, 2113.3.2 and 2113.4. In structures assigned to Seismic Design Category E or F, masonry chimneys shall be reinforced in accordance with the requirements of Sections 2101 through 2108 and anchored in accordance with Section 2113.4.

    2113.3.1 Vertical reinforcement. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars anchored in the foundation shall be placed in the concrete between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103.3. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof. 2113.3.2 Horizontal reinforcement. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete, or placed in the bed joints of unit masonry, at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

    2113.4 Seismic anchorage. Masonry chimneys and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.
  • CBC § 3.1 High relevance — show source text

    2113 A .3.1 Vertical reinforcement. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars anchored in the foundation shall be placed in the concrete between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103 A .3. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof.

    2025 CALIFORNIA BUILDING CODE 21A-13

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    MASONRY

    2113 A .3.2 Horizontal reinforcement. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete, or placed in the bed joints of unit masonry, at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

    2113 A .4 Seismic anchorage. Masonry chimneys and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.

    2113 A .5 Corbeling. Masonry chimneys shall not be corbeled more than half of the chimney’s wall thickness from a wall or foundation, nor shall a chimney be corbeled from a wall or foundation that is less than 12 inches (305 mm) in thickness unless it projects equally on each side of the wall, except that on the second story of a two-story dwelling, corbeling of chimneys on the exterior of the enclosing walls is permitted to equal the wall thickness. The projection of a single course shall not exceed one-half the unit height or one-third of the unit bed depth, whichever is less.

    2113 A .6 Changes in dimension. The chimney wall or chimney flue lining shall not change in size or shape within 6 inches (152 mm) above or below where the chimney passes through floor components, ceiling components or roof components.

  • CBC § 2113.3.2 High relevance — show source text

    Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof. 2113.3.2 Horizontal reinforcement. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete, or placed in the bed joints of unit masonry, at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

    2113.4 Seismic anchorage. Masonry chimneys and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.

    2113.5 Corbeling. Masonry chimneys shall not be corbeled more than half of the chimney’s wall thickness from a wall or foundation, nor shall a chimney be corbeled from a wall or foundation that is less than 12 inches (305 mm) in thickness unless it projects equally on each side of the wall, except that on the second story of a two-story dwelling, corbeling of chimneys on the exterior of the enclosing walls is permitted to equal the wall thickness. The projection of a single course shall not exceed one-half the unit height or onethird of the unit bed depth, whichever is less.

    2113.6 Changes in dimension. The chimney wall or chimney flue lining shall not change in size or shape within 6 inches (152 mm) above or below where the chimney passes through floor components, ceiling components or roof components.

    2113.7 Offsets. Where a masonry chimney is constructed with a fireclay flue liner surrounded by one wythe of masonry, the maximum offset shall be such that the centerline of the flue above the offset does not extend beyond the center of the chimney wall below the offset. Where the chimney offset is supported by masonry below the offset in an approved manner, the maximum offset limitations shall not apply. Each individual corbeled masonry course of the offset shall not exceed the projection limitations specified in Section 2113.5.

    2113.8 Additional load. Chimneys shall not support loads other than their own weight unless they are designed and constructed to support the additional load. Masonry chimneys are permitted to be constructed as part of the masonry walls or concrete walls of the building.

    2113.9 Termination. Chimneys shall extend not less than 2 feet (610 mm) higher than any portion of the building within 10 feet (3048 mm), but shall be not less than 3 feet (914 mm) above the highest point where the chimney passes through the roof.

  • CBC § 3.1 High relevance — show source text

    R1003.2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.

    R1003.3 Seismic reinforcing. Masonry or concrete chimneys shall be constructed, anchored, supported and reinforced as required in this chapter. In all structures regulated by this code assigned to Seismic Design Category C, D 0, D 1 or D 2 masonry and concrete chimneys shall be reinforced and anchored as detailed in Sections R1003.3.1, R1003.3.2 and R1003.4. In Seismic Design Category A or B, reinforcement and seismic anchorage are not required.

    R1003.3.1 Vertical reinforcing. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars, anchored in the foundation, shall be placed in the concrete, or between wythes of solid masonry, or within the cells of hollow unit masonry, and grouted in accordance with Section R608.1.1. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys more than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be installed for each additional 40 inches (1016 mm) in width or fraction thereof.

    R1003.3.2 Horizontal reinforcing. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete, or placed in the bed joints of unit masonry, at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be installed at each bend in the vertical bars.

    R1003.4 Seismic anchorage. Masonry and concrete chimneys and foundations in all structures regulated by this code assigned to Seismic Design Category C, D 0, D 1 or D 2 shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade, except where constructed completely within the exterior walls. Anchorage shall conform to the requirements in Section R1003.4.1. R1003.4.1 Anchorage. Two [3] / 16 -inch by 1-inch (5 mm by 25 mm) straps shall be embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor joists with two [1] / 2 -inch (12.7 mm) bolts. **R1003.4.1.1 Cold-formed steel framing.

  • CBC § 21-13 High relevance — show source text

    2025 CALIFORNIA BUILDING CODE 21-13

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    MASONRY

    supported by the body of the heater. Where the masonry chimney shares a common wall with the facing of the masonry heater, the chimney portion of the structure shall be reinforced in accordance with Section 2113.

    2112.5 Masonry heater clearance. Combustible materials shall not be placed within 36 inches (914 mm) or the distance of the allowed reduction method from the outside surface of a masonry heater in accordance with NFPA 211, Section 12.6, and the required space between the heater and combustible material shall be fully vented to permit the free flow of air around all heater surfaces.

    Exceptions:

    1. Where the masonry heater wall thickness is not less than 8 inches (203 mm) of solid masonry and the wall thickness of the heat exchange channels is not less than 5 inches (127 mm) of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
    2. Masonry heaters listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.

    SECTION 2113—MASONRY CHIMNEYS

    2113.1 General. The construction of masonry chimneys consisting of solid masonry units, hollow masonry units grouted solid, stone or concrete shall be in accordance with this section.

    2113.2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.

    2113.3 Seismic reinforcement. In structures assigned to Seismic Design Category A or B, seismic reinforcement is not required. In structures assigned to Seismic Design Category C or D, masonry chimneys shall be reinforced and anchored in accordance with Sections 2113.3.1, 2113.3.2 and 2113.4. In structures assigned to Seismic Design Category E or F, masonry chimneys shall be reinforced in accordance with the requirements of Sections 2101 through 2108 and anchored in accordance with Section 2113.4.

    2113.3.1 Vertical reinforcement. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars anchored in the foundation shall be placed in the concrete between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103.3. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof. **2113.3.2 Horizontal reinforcement.

  • CBC § 2.1 High relevance — show source text

    R1001.2 Footings and foundations. Footings for masonry fireplaces and their chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the fireplace or foundation wall on all sides. Footings shall be founded on natural, undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.

    R1001.2.1 Ash dump cleanout. Cleanout openings located within foundation walls below fireboxes, where provided, shall be equipped with ferrous metal or masonry doors and frames constructed to remain tightly closed except when in use. Cleanouts shall be located to allow access so that ash removal will not create a hazard to combustible materials.

    R1001.3 Seismic reinforcing. Masonry or concrete chimneys in all structures regulated by this code assigned to Seismic Design Category C, D 0, D 1 or D 2 shall be reinforced. Reinforcing shall conform to the requirements set forth in Table R1001.1 and Section R606.

    R1001.3.1 Vertical reinforcing. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars shall be placed between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section R606. Grout

    10-4 2025 CALIFORNIA RESIDENTIAL CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    CHIMNEYS AND FIREPLACES

    shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys more than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional flue incorporated into the chimney or for each additional 40 inches (1016 mm) in width or fraction thereof. R1001.3.2 Horizontal reinforcing. Vertical reinforcement shall be placed within [1] / 4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, placed in the bed joints in accordance with Section R606 at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be installed at each bend in the vertical bars.

    R1001.4 Seismic anchorage. Masonry or concrete chimneys in all structures regulated by this code assigned to Seismic Design Category C, D 0, D 1 or D 2 shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade, except where constructed completely within the exterior walls. Anchorage shall conform to the requirements of Section R1001.4.1. R1001.4.1 Anchorage. Two [3] / 16 -inch by 1-inch (5 mm by 25 mm) straps shall be embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor ceiling or floor joists or rafters with two [1] / 2 -inch (12.7 mm) bolts. **R1001.4.1.1 Cold-formed steel framing.

  • CBC § 2111.4 High relevance — show source text

    2111.4 Seismic reinforcement. In structures assigned to Seismic Design Category A or B, seismic reinforcement is not required. In structures assigned to Seismic Design Category C or D, masonry fireplaces shall be reinforced and anchored in accordance with Sections 2111.4.1, 2111.4.2 and 2111.5. In structures assigned to Seismic Design Category E or F, masonry fireplaces shall be reinforced in accordance with the requirements of Sections 2101 through 2108.

    2111.4.1 Vertical reinforcing. For fireplaces with chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars, anchored in the foundation, shall be placed in the concrete between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103.3. For fireplaces with chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof. 2111.4.2 Horizontal reinforcing. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete; or placed in the bed joints of unit masonry at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

    2111.5 Seismic anchorage. Masonry fireplaces and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not fewer than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.

    2025 CALIFORNIA BUILDING CODE 21-11

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    MASONRY

    2111.6 Firebox walls. Masonry fireboxes shall be constructed of solid masonry units, hollow masonry units grouted solid, stone or concrete. Where a lining of firebrick not less than 2 inches (51 mm) in thickness or other approved lining is provided, the minimum thickness of back and sidewalls shall each be 8 inches (203 mm) of solid masonry, including the lining. The width of joints between firebricks shall be not greater than [1] / 4 inch (6.4 mm). Where a lining is not provided, the total minimum thickness of back and sidewalls shall be 10 inches (254 mm) of solid masonry. Firebrick shall conform to ASTM C27 or ASTM C1261 and shall be laid with medium-duty refractory mortar conforming to ASTM C199.

    **2111.6.1 Steel fireplace units.

  • CBC § 3.1 High relevance — show source text

    Exceptions:

    1. Where the masonry heater wall thickness is not less than 8 inches (203 mm) of solid masonry and the wall thickness of the heat exchange channels is not less than 5 inches (127 mm) of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
    2. Masonry heaters listed and labeled in accordance with UL 1482 or EN 15250 and installed in accordance with the manufacturer’s instructions.

    SECTION 2113 A —MASONRY CHIMNEYS

    2113 A .1 General. The construction of masonry chimneys consisting of solid masonry units, hollow masonry units grouted solid, stone or concrete shall be in accordance with this section.

    2113 A .2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.

    2113 A .3 Seismic reinforcement. In structures assigned to Seismic Design Category A or B, seismic reinforcement is not required. In structures assigned to Seismic Design Category C or D, masonry chimneys shall be reinforced and anchored in accordance with Sections 2113 A .3.1, 2113 A .3.2 and 2113 A .4. In structures assigned to Seismic Design Category E or F, masonry chimneys shall be reinforced in accordance with the requirements of Sections 2101 through 2108 and anchored in accordance with Section 2113 A .4.

    2113 A .3.1 Vertical reinforcement. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars anchored in the foundation shall be placed in the concrete between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103 A .3. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof.

    2025 CALIFORNIA BUILDING CODE 21A-13

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    MASONRY

    2113 A .3.2 Horizontal reinforcement. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete, or placed in the bed joints of unit masonry, at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

  • CBC § 3.1 High relevance — show source text

    2111 A .3.1 Ash dump cleanout. Cleanout openings, located within foundation walls below fireboxes, where provided, shall be equipped with ferrous metal or masonry doors and frames constructed to remain tightly closed, except when in use. Cleanouts shall be accessible and located so that ash removal will not create a hazard to combustible materials.

    2111 A .4 Seismic reinforcement. In structures assigned to Seismic Design Category A or B, seismic reinforcement is not required. In structures assigned to Seismic Design Category C or D, masonry fireplaces shall be reinforced and anchored in accordance with Sections 2111 A .4.1, 2111 A .4.2 and 2111 A .5. In structures assigned to Seismic Design Category E or F, masonry fireplaces shall be reinforced in accordance with the requirements of Sections 2101 A through 2108 A .

    2111 A .4.1 Vertical reinforcing. For fireplaces with chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars, anchored in the foundation, shall be placed in the concrete between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section 2103.3. For fireplaces with chimneys greater than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional 40 inches (1016 mm) in width or fraction thereof. 2111 A .4.2 Horizontal reinforcing. Vertical reinforcement shall be placed enclosed within [1] / 4 -inch (6.4 mm) ties or other reinforcing of equivalent net cross-sectional area, spaced not to exceed 18 inches (457 mm) on center in concrete; or placed in the bed joints of unit masonry at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.

    2111 A .5 Seismic anchorage. Masonry fireplaces and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not fewer than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.
  • CBC § 8-7 High relevance — show source text

    R1002.5 Masonry heater clearance. Combustible materials shall not be placed within 36 inches (914 mm) of the outside surface of a masonry heater in accordance with NFPA 211 Section 8-7 (clearances for solid-fuel-burning appliances), and the required space between the heater and combustible material shall be fully vented to permit the free flow of air around all heater surfaces.

    Exceptions:

    1. Where the masonry heater wall is not less than 8 inches (203 mm) thick of solid masonry and the wall of the heat exchange channels is not less than 5 inches (127 mm) thick of solid masonry, combustible materials shall not be placed within 4 inches (102 mm) of the outside surface of a masonry heater. A clearance of not less than 8 inches (203 mm) shall be provided between the gas-tight capping slab of the heater and a combustible ceiling.
    2. Masonry heaters listed and labeled in accordance with UL 1482 or CEN 15250 shall be installed in accordance with the listing specifications and the manufacturer’s written instructions.

    SECTION R1003—MASONRY CHIMNEYS

    R1003.1 Definition. A masonry chimney is a chimney constructed of solid masonry units, hollow masonry units grouted solid, stone or concrete, hereinafter referred to as masonry. Masonry chimneys shall be constructed, anchored, supported and reinforced as required in this chapter.

    R1003.2 Footings and foundations. Footings for masonry chimneys shall be constructed of concrete or solid masonry not less than 12 inches (305 mm) thick and shall extend not less than 6 inches (152 mm) beyond the face of the foundation or support wall on all sides. Footings shall be founded on natural undisturbed earth or engineered fill below frost depth. In areas not subjected to freezing, footings shall be not less than 12 inches (305 mm) below finished grade.

    R1003.3 Seismic reinforcing. Masonry or concrete chimneys shall be constructed, anchored, supported and reinforced as required in this chapter. In all structures regulated by this code assigned to Seismic Design Category C, D 0, D 1 or D 2 masonry and concrete chimneys shall be reinforced and anchored as detailed in Sections R1003.3.1, R1003.3.2 and R1003.4. In Seismic Design Category A or B, reinforcement and seismic anchorage are not required.

    R1003.3.1 Vertical reinforcing. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars, anchored in the foundation, shall be placed in the concrete, or between wythes of solid masonry, or within the cells of hollow unit masonry, and grouted in accordance with Section R608.1.1. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys more than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be installed for each additional 40 inches (1016 mm) in width or fraction thereof.

  • CBC § 4.8 High relevance — show source text

    2113 A .4 Seismic anchorage. Masonry chimneys and foundations shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade with two [3] / 16 -inch by 1-inch (4.8 mm by 25 mm) straps embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor joists with two [1] / 2 -inch (12.7 mm) bolts.

    Exception: Seismic anchorage is not required for the following:

    1. In structures assigned to Seismic Design Category A or B.
    2. Where the masonry fireplace is constructed completely within the exterior walls.

    2113 A .5 Corbeling. Masonry chimneys shall not be corbeled more than half of the chimney’s wall thickness from a wall or foundation, nor shall a chimney be corbeled from a wall or foundation that is less than 12 inches (305 mm) in thickness unless it projects equally on each side of the wall, except that on the second story of a two-story dwelling, corbeling of chimneys on the exterior of the enclosing walls is permitted to equal the wall thickness. The projection of a single course shall not exceed one-half the unit height or one-third of the unit bed depth, whichever is less.

    2113 A .6 Changes in dimension. The chimney wall or chimney flue lining shall not change in size or shape within 6 inches (152 mm) above or below where the chimney passes through floor components, ceiling components or roof components.

    2113 A .7 Offsets. Where a masonry chimney is constructed with a fireclay flue liner surrounded by one wythe of masonry, the maximum offset shall be such that the centerline of the flue above the offset does not extend beyond the center of the chimney wall below the offset. Where the chimney offset is supported by masonry below the offset in an approved manner, the maximum offset limitations shall not apply. Each individual corbeled masonry course of the offset shall not exceed the projection limitations specified in Section 2113 A .5.

    2113 A .8 Additional load. Chimneys shall not support loads other than their own weight unless they are designed and constructed to support the additional load. Masonry chimneys are permitted to be constructed as part of the masonry walls or concrete walls of the building.

    2113 A .9 Termination. Chimneys shall extend not less than 2 feet (610 mm) higher than any portion of the building within 10 feet (3048 mm), but shall be not less than 3 feet (914 mm) above the highest point where the chimney passes through the roof.

    2113 A .9.1 Chimney caps. Masonry chimneys shall have a concrete, metal or stone cap, sloped to shed water, a drip edge and a caulked bond break around any flue liners in accordance with ASTM C1283.

    2113 A .9.2 Spark arrestors. [SFM] All chimneys attached to any appliance or fireplace that burns solid fuel shall be equipped with an approved spark arrester. The spark arrestor shall meet all of the following requirements: 1.

  • CBC § 12.7 Medium relevance — show source text

    (12.7 mm) in diameter. (b) Vertical spacing of lateral ties, over the full height of the column, shall not exceed 8 longitudinal bar diameters, 24 lateral tie bar diameters, 8 inches (203 mm), or one-half the least cross-sectional dimension of the member. (d) Lateral ties shall be embedded in grout. (e) Lateral ties shall be located vertically not more than one-half lateral tie spacing above the top of the footing or slab in any story, and shall be spaced not more than one-half a lateral tie spacing nor 2 inches (51 mm) below the lowest horizontal reinforcement in beam, girder, slab, or drop panel above. The top tie shall be within 2 inches (51 mm) of the top of the column.

    2115.5.2 TMS 402, Section 7.3.2.5 (i). Replace first sentence of TMS 402, Section 7.3.2.5 (i) by the following: (i) When the ratio of V/F vm A mv for masonry designed in accordance with Chapter 8 or when the ratio V u /ΦV nm for masonry designed in accordance with Chapter 9 exceeds 0.15, or the h w /l w exceeds 0.5, the termination of horizontal reinforcement embedded in grout shall meet one of the following:

    2115.5.3 TMS 402, Sections 7.4.4.1 and 7.4.5.1. Replace TMS 402, Section 7.4.4.1 as follows and delete Section 7.4.5.1:

    7.4.4.1 Minimum reinforcement requirements for masonry walls. The total area of reinforcement in reinforced masonry walls shall not be less than 0.003 times the sectional area of the wall. Neither the horizontal nor the vertical reinforcement shall be less than one third of the total. Horizontal and vertical reinforcement shall be spaced at not more than 24 inches (610 mm) center to center. Where other than running bond is used in reinforced hollow unit masonry, the open-end type of unit shall be used with vertical reinforcement spaced a maximum of 16 inches (406 mm) on center.

    Exception: Reinforced hollow unit masonry used for freestanding site walls or interior nonbearing nonshear wall partitions shall have horizontal reinforcing spaced not more than 4 feet (1.2 m) on center, except for locations in Seismic Design Category F, and may be grouted only in cells containing vertical and horizontal reinforcement.

    7.4.4.1.1 The minimum reinforcing shall be No. 4, except that No. 3 bars may be used for ties and stirrups. Vertical wall reinforce- ment shall have dowels of equal size and equally matched spacing in all footings. Reinforcement shall be continuous around wall corners and through intersections. Only reinforcement which is continuous in the wall shall be considered in computing the

    2025 CALIFORNIA BUILDING CODE 21-21

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    MASONRY

    minimum area of reinforcement. Reinforcement with splices conforming to TMS 402 shall be considered as continuous reinforcement.

Frequently asked questions

Do the prescriptive reinforcement rules apply in all seismic design categories?

No. The prescriptive rules in § 2113.3 apply for SDC C and D; SDC A/B do not require seismic reinforcement and SDC E/F must follow the full reinforced masonry design in §§ 2101–2108.

How many No. 4 bars are needed for a 95‑inch wide chimney?

Start with four No. 4 bars for the first 40 in.; add two bars for each additional 40‑in. or fraction. 95 in. = 40 + 40 + 15 (fraction) → 4 + 2 + 2 = 8 No. 4 vertical bars per § 2113.3.1.

Can I bond the grout to the flue liner to secure it?

No. Grout shall be prevented from bonding with the flue liner so the liner remains free to move with thermal expansion (see § 2113.3.1).

Where and how deep must seismic straps be embedded?

Two 3/16" × 1" straps must be embedded not less than 12 in. into the chimney; straps are hooked around the outer bars and extend 6 in. beyond the bend (§ 2113.4).

If the chimney is built entirely inside the exterior walls, do I still need seismic anchors?

If the masonry fireplace (and its chimney) is constructed completely within the exterior walls, the seismic anchorage requirement is excepted per the exception in § 2113.4.

More in California Building Code

Ask about the CBC

Get cited, plain-English answers on the California Building Code for your project — any code section, any scenario.

Start Free Trial

Related in the CBC

Masonry fireplaces: construction requirements, clearances and seismic anchorage exceptions

Masonry heaters: definition, installation standards, footing requirements and seismic reinforcing

Chimneys, fireplaces and masonry heaters

California Building Code