CBC · California Building Code

Masonry fireplaces: construction requirements, clearances and seismic anchorage exceptions

For homeowners: California’s Building Code requires masonry fireplaces to sit on 12‑inch footings, meet minimum firebox thicknesses and dimensions, be reinforced in many seismic zones (with specific No. 4 bar counts and tie spacing), and in applicable areas be anchored with two metal straps embedded into the chimney and bolted to joists — but anchorage is not required in low seismic categories or when the fireplace is fully within exterior walls; see §§2111 and 2113.4 for the exact rules and exceptions.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

Masonry fireplaces and their chimneys must be built on concrete or solid-masonry footings, have specified firebox wall thicknesses and minimum dimensions, and in many seismic zones must be reinforced and anchored to resist earthquake forces. The controlling provisions are in §2111 for masonry fireplaces (footings, firebox construction, clearances, reinforcement) and §2113 (chimneys), with specific anchorage requirements in §2111.5 and §2113.4.

Requirements in detail

Footings / foundations

  • Footings for masonry fireplaces and their chimneys must be concrete or solid masonry not less than 12 inches (305 mm) thick and must extend at least 6 inches beyond the face of the fireplace or foundation on all sides; they must bear on undisturbed earth or engineered fill below frost depth. See §2111.3.

Firebox construction and dimensions

  • Firebox wall materials: solid masonry units, hollow masonry units grouted solid, stone or concrete. Where a 2-inch (51 mm) firebrick lining is used, the back and sidewalls must be at least 8 inches (203 mm) of solid masonry including the lining; without a lining, the back and sidewalls must be at least 10 inches (254 mm) of solid masonry. Firebrick/joint and mortar specifications are identified in §2111.6.
  • Minimum firebox depth: 20 inches (508 mm) (with an exception for Rumford fireplaces under defined proportions). Throat (damper) and smoke-chamber cross-sectional rules are in §2111.7.
  • Masonry over the opening must be supported by a noncombustible lintel with a minimum 4-inch bearing at each end; the throat/damper must be at least 8 inches (203 mm) above the fireplace opening. See §2111.8.

Reinforcement (vertical and horizontal)

  • Seismic reinforcement is required based on Seismic Design Category (SDC): none required in SDC A or B; required in C and D per the reinforcement rules; SDC E/F must follow Sections 2101–2108 for reinforcement. See §2111.4.
  • Vertical reinforcing for fireplaces (and for chimneys in §2113): for chimneys up to 40 inches (1016 mm) wide, provide four No. 4 continuous vertical bars anchored in the foundation. For widths greater than 40 inches, add two additional No. 4 bars for each additional 40 inches (or fraction thereof). See §2111.4.1 and §2113.3.1.
  • Horizontal reinforcement / ties: vertical reinforcement must be enclosed by 1/4‑inch (6.4 mm) ties (or equivalent) spaced not more than 18 inches (457 mm) on center in concrete, or placed in unit-masonry bed joints at not less than every 18 inches of vertical height; provide two ties at each bend in the vertical bars. See §2111.4.2 and §2113.3.2.

Seismic anchorage (straps, embedment, fastenings)

  • Where anchorage is required (see exceptions below), masonry fireplaces and foundations must 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 × 25 mm) straps. Straps must be embedded not less than 12 inches (305 mm) into the chimney, hooked around the outer vertical bars, extend 6 inches (152 mm) beyond the bend, and each strap must be fastened to not fewer than four floor joists with two 1/2‑inch (12.7 mm) bolts. See §2111.5 and §2113.4.

Clearances and combustible materials

  • General clearance provisions are described in §2111 and illustrated by Figure 2111.A.12; there are explicit exceptions that permit combustible trim and mantels in certain locations and with specified minimum distances and projection limits (for example, combustible mantels may be placed directly on the masonry front provided they are not within 6 inches (153 mm) of the fireplace opening and projection rules are followed). See §2111 exceptions and Figure 2111.A.12 for the detailed allowances.
  • Specific clearance distances for masonry heaters (different product) are in §2112 and are separate from the masonry‑fireplace rules (for example, 36 inches or reduction-per-NFPA allowance). If working with masonry heaters, consult §2112.

Fireblocking and exterior air

  • All spaces between fireplaces and floors/ceilings through which fireplaces pass must be fireblocked with noncombustible material. See §2111.13.
  • Factory-built or masonry fireplaces covered in the section must be equipped with an exterior combustion‑air supply unless the room is mechanically ventilated and neutral/positive pressure is maintained; factory-built units must have listed exterior air ducts installed per the manufacturer. See §2111.14 and §2111.14.1.

Decision‑relevant dimensions & values (summary table)

Item Value / Dimension Where in CBC (section) Code Reference
Footing thickness (fireplace, chimney) ≥ 12 in (305 mm) §2111.3 / §2113.2
Footing projection beyond face ≥ 6 in (152–153 mm) §2111.3 / §2113.2
Firebox back & sidewall thickness (with lining) ≥ 8 in (203 mm) incl. 2 in firebrick §2111.6
Firebox back & sidewall thickness (no lining) ≥ 10 in (254 mm) §2111.6
Minimum firebox depth ≥ 20 in (508 mm) (Rumford exception exists) §2111.7
Vertical reinforcement (chimney/fireplace ≤ 40 in) 4 — No. 4 continuous bars anchored in foundation §2111.4.1 / §2113.3.1
Additional vertical bars for >40 in width +2 No. 4 for each extra 40 in (or fraction) §2111.4.1 / §2113.3.1
Horizontal tie spacing ≤ 18 in (457 mm) o.c.; 2 ties at each bar bend §2111.4.2 / §2113.3.2
Seismic anchorage straps Two 3/16 in × 1 in straps; embed ≥ 12 in; extend 6 in past bend; attach to ≥4 joists with two 1/2 in bolts §2111.5 / §2113.4
Minimum chimney wall thickness ≥ 4 in (102 mm) nominal §2113.10
Chimney clearance (medium‑heat appliances) ≥ 4 in (102 mm) to combustibles (specific to medium-heat chimneys) §2113.11.2.5
Chimney termination heights 2 ft above any building portion within 10 ft; at least 3 ft above roof penetration point §2113.9

(Each row above is taken directly from the applicable CBC text cited in the Code Reference column.)

Exceptions & special cases

  • Seismic anchorage not required in SDC A or B, or when the masonry fireplace is constructed completely within the exterior walls — see the exception language to §2111.5 and §2113.4.
  • SDC E and F: fireplaces and chimneys in those high seismic categories must be reinforced per the more general Sections 2101–2108 rather than the prescriptive §2111.4/§2113.3 methods. See §2111.4 and §2113.3.
  • Steel fireplace units are permitted within solid masonry fireplaces when installed per their listing or the section’s requirements; steel-lined units have minimum steel thickness and masonry encasement requirements (§2111.6.1).
  • Masonry heaters and their clearances are governed in §2112 (different rules, larger clearances unless the heater meets specified mass/thickness or is listed). Do not mix masonry‑heater clearance rules with ordinary fireplaces.

If you need a compliance path in SDC E/F, consult Sections 2101–2108 (these provisions govern reinforced masonry strength/design) because §2111/§2113 direct you to them for E/F rather than providing prescriptive laydown.

Common mistakes

  • Assuming anchorage applies only to chimneys: the code requires anchoring “masonry fireplaces and foundations” at each story line more than 6 ft above grade — don’t omit fireplace anchorage when applicable. See §2111.5.
  • Misreading the “constructed completely within the exterior walls” exception — it means the masonry mass is fully contained within the plane of the exterior walls (interior massing), not simply that the fireplace touches the exterior wall face; verify with plan details and the building official. See §2111.5 exception.
  • Wrong strap embedment, size or fastening: straps must be the specified 3/16″ × 1″, embedded ≥12″ into the chimney, hooked and extended 6″, and fastened to ≥4 joists with two 1/2″ bolts — substitution or short embedment can fail the seismic anchorage requirement. See §2111.5/§2113.4.
  • Insufficient vertical reinforcement for wider chimneys/fireplaces: for each fractional 40‑inch increment add two No.4 bars; failing to add them for, e.g., a 41–79 in wide chimney is noncompliant. See §2111.4.1 and §2113.3.1.
  • Overlooking firebrick and mortar specs: firebrick thickness, ASTM references and mortar type are specified — using nonconforming brick or wrong mortar can violate §2111.6.

Worked example — single example with numbers

Scenario: A one‑family dwelling located in Seismic Design Category C has a masonry fireplace whose chimney is 48 inches wide and the chimney passes up through the second floor roof so the chimney is anchored at an intermediate floor line more than 6 ft above grade.

  1. Reinforcement:
    • Width 48 in → chimney/fireplace is >40 in and ≤80 in → base requirement: 4 No. 4 continuous vertical bars for the first 40 in plus 2 additional No. 4 bars for the fraction over 40 in → total = 6 No. 4 continuous vertical bars anchored in the foundation. (See §2111.4.1 and §2113.3.1.)
  2. Horizontal ties:
    • Place 1/4‑inch ties (or equivalent) enclosing the vertical bars at ≤18 in vertical spacing; provide two ties at each bend in the vertical bars. (See §2111.4.2.)
  3. Anchorage straps:
    • Because the chimney passes a floor/ceiling line >6 ft above grade and the house is in SDC C, seismic anchorage is required. Provide two 3/16″ × 1″ straps embedded ≥12″ into the chimney; hook around the outer vertical bars and extend 6″ beyond the bend; fasten each strap to at least four floor joists with two 1/2″ bolts. (See §2111.5.)
  4. Footing:
    • Provide a concrete footing ≥12″ thick and extend it ≥6″ beyond the fireplace/chimney face; found on undisturbed earth or engineered fill below frost depth. (See §2111.3/§2113.2.)
  5. Firebox:
    • If you use a 2″ firebrick lining, design back and sidewalls to be 8″ of solid masonry (including the lining); ensure minimum firebox depth 20″ and throat ≥8″ above opening per §2111.6 and §2111.7.

If instead the same fireplace were constructed completely within the exterior walls (i.e., its masonry mass entirely within the exterior wall plane such that it is not an exposed mass beyond the exterior wall), the anchor requirement at the floor/ceiling line would not apply by the §2111.5 exception — but verify this interpretation with the local building official because the phrase is a common trigger for differing local interpretations.

Related provisions (quick list)

  • §2111 — Masonry fireplaces (general, drawings, footings, firebox, reinforcement)
  • §2111.3 — Footings and foundations for fireplaces
  • §2111.4 / §2111.4.1 / §2111.4.2 — Seismic reinforcement; vertical and horizontal reinforcing rules for fireplaces
  • §2111.5 — Seismic anchorage requirements and exceptions for fireplaces
  • §2111.6 / §2111.6.1 — Firebox wall construction and steel fireplace unit allowances
  • §2111.7 — Firebox dimensions (depth, throat, smoke chamber)
  • §2111.13 / §2111.14 — Fireblocking and exterior combustion air for fireplaces
  • §2113 / §2113.2 / §2113.3 / §2113.4 — Masonry chimneys: footings, reinforcement and seismic anchorage (parallels fireplace anchorage rules)
  • §2112 — Masonry heaters (entirely separate appliance-specific provisions and different clearances)

Code references

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

  • 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 § 2103.3. High relevance — show source text

    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.

    2111 A .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 A .6.1 Steel fireplace units. Steel fireplace units are permitted to be installed with solid masonry to form a masonry fireplace provided that they are installed according to either the requirements of their listing or the requirements of this section. Steel fireplace units incorporating a steel firebox lining shall be constructed with steel not less than [1] / 4 inch (6.4 mm) in thickness, and an aircirculating chamber that is ducted to the interior of the building. The firebox lining shall be encased with solid masonry to provide a total thickness at the back and sides of not less than 8 inches (203 mm), of which not less than 4 inches (102 mm) shall be of solid masonry or concrete. Circulating air ducts employed with steel fireplace units shall be constructed of metal or masonry.

  • 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 § 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 § 404.6 High relevance — show source text

    Exceptions:

    1. Glass-block assemblies having a fire protection rating of not less than [3] / 4 hour shall be permitted as opening protectives in accordance with Section 716 in fire barriers, fire partitions and smoke barriers that have a required fireresistance rating of 1 hour or less and do not enclose exit stairways and ramps or exit passageways.
    2. Glass-block assemblies as permitted in Section 404.6, Exception 2.

    SECTION 2111—MASONRY FIREPLACES

    2111.1 General. The construction of masonry fireplaces, consisting of concrete or masonry, shall be in accordance with this section.

    2111.2 Fireplace drawings. The construction documents shall describe in sufficient detail the location, size and construction of masonry fireplaces. The thickness and characteristics of materials and the clearances from walls, partitions and ceilings shall be indicated.

    2111.3 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 (153 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.

    2111.3.1 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.

    2111.4 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.

  • 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 § 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 § 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.

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    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 § 21-11 High relevance — show source text

    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.

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    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. Steel fireplace units are permitted to be installed with solid masonry to form a masonry fireplace provided that they are installed according to either the requirements of their listing or the requirements of this section. Steel fireplace units incorporating a steel firebox lining shall be constructed with steel not less than [1] / 4 inch (6.4 mm) in thickness, and an aircirculating chamber that is ducted to the interior of the building. The firebox lining shall be encased with solid masonry to provide a total thickness at the back and sides of not less than 8 inches (203 mm), of which not less than 4 inches (102 mm) shall be of solid masonry or concrete. Circulating air ducts employed with steel fireplace units shall be constructed of metal or masonry.

    2111.7 Firebox dimensions. The firebox of a concrete or masonry fireplace shall have a minimum depth of 20 inches (508 mm). The throat shall be not less than 8 inches (203 mm) above the fireplace opening. The throat opening shall be not less than 4 inches (102 mm) in depth. The cross-sectional area of the passageway above the firebox, including the throat, damper and smoke chamber, shall be not less than the cross-sectional area of the flue.

    Exception: Rumford fireplaces shall be permitted provided that the depth of the fireplace is not less than 12 inches (305 mm) and not less than one-third of the width of the fireplace opening, and the throat is not less than 12 inches (305 mm) above the lintel, and not less than [1] / 20 the cross-sectional area of the fireplace opening.

    2111.8 Lintel and throat. Masonry over a fireplace opening shall be supported by a lintel of noncombustible material. The minimum required bearing length on each end of the fireplace opening shall be 4 inches (102 mm). The fireplace throat or damper shall be located not less than 8 inches (203 mm) above the top of the fireplace opening.

  • 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 § 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.

Frequently asked questions

When is seismic anchorage required for a masonry fireplace?

Seismic anchorage is required where a fireplace or chimney crosses a floor, ceiling, or roof line that is more than 6 feet above grade except in Seismic Design Categories A and B or when the fireplace is constructed completely within the exterior walls; see §2111.5 and §2113.4.

How many vertical reinforcing bars are needed for a 48‑inch‑wide chimney?

For up to 40 in width use four No. 4 continuous vertical bars; for 48 in add two additional No. 4 bars (one increment of “additional 40 in or fraction thereof”), giving 6 total No. 4 bars; see §2111.4.1 and §2113.3.1.

Can combustible mantels be installed on a masonry fireplace?

Yes — the code allows combustible mantels to be placed directly on a masonry front provided they are not within 6 inches (153 mm) of the fireplace opening and projection limits are honored; see the exceptions and Figure 2111.A.12 in §2111.

Are masonry heaters covered by the same clearances as masonry fireplaces?

No — masonry heaters are covered under §2112 and have separate clearance rules (for example, 36 inches unless certain mass/thickness or listing conditions apply); do not substitute §2111 fireplace clearances for masonry heaters.

What are the required anchor strap details?

Two 3/16″ by 1″ straps embedded at least 12″ into the chimney, hooked around outer bars, extended 6″ beyond the bend, and each fastened to not fewer than four floor joists with two 1/2″ bolts — see §2111.5 / §2113.4.

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