CRC · California Residential Code

What seismic reinforcing and anchorage are required for masonry fireplaces and chimneys?

If your masonry fireplace or chimney is in Seismic Design Category C or higher, the CRC requires continuous vertical reinforcement (four No. 4 bars for chimneys up to 40 in wide, plus two No. 4 for each additional 40 in or flue), horizontal ties at 18‑inch spacing, and anchorage straps embedded 12 inches and fastened to not fewer than four joists where the chimney crosses floor/roof lines more than 6 feet above grade (see §§ R1001.3 and R1001.3.1).

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

In short: masonry fireplaces and chimneys located in buildings assigned to Seismic Design Category C, D0, D1 or D2 must be reinforced and anchored. The prescriptive vertical reinforcement is four No. 4 continuous vertical bars for chimneys up to 40 inches wide (with additional bars for larger chimneys) under § R1001.3 and § R1001.3.1. Anchorage straps and their embedment/fastening details are required where the chimney passes a floor/ceiling/roof line more than 6 feet above grade. See § R1001.3, § R1001.3.1 and the anchorage sections for the exact details .

The single most important rule: if the chimney/fireplace is in Seismic Design Category C or higher, provide the prescribed vertical steel, horizontal ties and floor/roof anchorage exactly as the CRC requires.

Requirements in detail

Applicability (when these rules apply)

  • The reinforcement and anchorage rules apply in Seismic Design Category C, D0, D1 or D2; they are not required in Category A or B. See § R1001.3 for the applicability statement .

Vertical reinforcing (primary load-resisting element)

  • For chimneys up to 40 inches (1016 mm) wide: install four No. 4 continuous vertical bars, placed between wythes or within cells and grouted. Grout must be placed so the flue liner is free to move (i.e., grout prevented from bonding to the flue liner). These rules are in § R1001.3.1 .
  • For chimneys wider than 40 inches: add two additional No. 4 vertical bars for each additional 40 inches of width or fraction thereof, or for each additional flue incorporated into the chimney (see § R1001.3.1) .

Horizontal reinforcing / ties

  • Provide horizontal ties or equivalent (typically 1/4‑inch ties) in bed joints or enclosed ties so vertical reinforcement is held at spacing not exceeding 18 inches (457 mm) of vertical height; install two ties at each bend in the vertical bars. See § R1001.3.2 for the horizontal tie spacing and bend requirement .

Seismic anchorage (where and how to anchor)

  • Anchor chimneys at every floor, ceiling or roof line that is more than 6 feet (1829 mm) above grade, except when the chimney is constructed completely within exterior walls. (See § R1001.4.)
  • Typical anchor detail: two 3/16‑inch by 1‑inch straps, each embedded not less than 12 inches (305 mm) into the chimney, hooked around the outer bars and extending 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor/ceiling joists or rafters with two 1/2‑inch (12.7 mm) bolts (see § R1001.4.1) .

Key defined terms (first mention highlighted)

  • Seismic Design Category — determines whether the reinforcement/anchorage provisions apply (see § R1001.3) .
  • No. 4 — reinforcing bar size specified for vertical bars in § R1001.3.1 .

Decision‑relevant quick table

Item Required Value / Threshold Code Reference
Seismic categories requiring reinforcement C, D0, D1, D2 § R1001.3
Vertical bars (chimney ≤ 40 in wide) 4 × No. 4 continuous vertical bars § R1001.3.1
Additional vertical bars (per extra width/flue) +2 × No. 4 per additional 40 in or fraction § R1001.3.1
Horizontal tie spacing ≤ 18 in vertical spacing; 2 ties at each bend § R1001.3.2
Floor/roof anchorage trigger When chimney crosses floor/ceiling/roof line > 6 ft above grade § R1001.4
Anchorage straps Two straps, 3/16 in × 1 in, embed 12 in, extend 6 in, hook around outer bars § R1001.4.1
Fastening for straps Fasten to ≥ 4 joists/rafters with 2 — 1/2 in bolts § R1001.4.1
Grout and flue liner Grout must be placed so the flue liner is free to move (don’t bond grout to liner) § R1001.3.1
Summary table of fireplace/chimney requirements See Table R1001.1 for a consolidated summary Table R1001.1 (R1001 chapter)

Exceptions & special cases

  • Reinforcement and seismic anchorage are not required in Seismic Design Category A or B (see § R1001.3) .
  • Anchorage is not required where the masonry fireplace/chimney is constructed completely within the exterior walls (see § R1001.4 for the exception) .
  • Grout must be placed so the flue liner is free to move (thermal expansion): do not let grout bond to the liner (see § R1001.3.1) .
  • If your configuration includes multiple flues or a chimney wider than 40 inches, the “per additional flue / per 40‑inch fraction” rule increases required vertical bars — treat each flue or each 40‑inch increment as adding two No.4 bars (§ R1001.3.1) .

Common mistakes

  • Assuming these rules apply only to tall chimneys — the trigger is crossing a floor/ceiling/roof line more than 6 ft above grade, not just total height. See § R1001.4 .
  • Forgetting the grout/flue separation requirement — bonding grout to the flue liner violates § R1001.3.1 and can prevent needed thermal movement .
  • Using the wrong number of vertical bars for chimneys wider than 40 in. For width > 40 in add two No. 4 bars per extra 40 in or fraction (§ R1001.3.1) .
  • Installing anchors but attaching them to fewer than four joists or using undersized bolts — the anchors must be fastened to not less than four joists with two 1/2‑inch bolts per strap per § R1001.4.1 .
  • Omitting horizontal ties or spacing them more than 18 in on center — horizontal reinforcement spacing is mandatory (§ R1001.3.2) .

Worked example — concrete scenario

Scenario: A single‑family dwelling in Seismic Design Category D1 has a masonry chimney that is 62 inches wide and crosses the first‑floor ceiling line; the top of that floor line is more than 6 feet above grade.

Step 1 — Vertical bars:

  • Base requirement for ≤ 40 in: 4 × No. 4 continuous vertical bars. (§ R1001.3.1)
  • Chimney is 62 in → that is >40 in and less than 80 in, so add 2 × No. 4 (one increment/fraction of 40 in). Total = 6 × No. 4 vertical bars. (§ R1001.3.1)

Step 2 — Horizontal ties:

  • Install horizontal ties (or equivalent) at not more than 18 in vertical spacing; place two ties at each bend of the vertical bars. (§ R1001.3.2)

Step 3 — Anchorage at the floor/ceiling line:

  • Because the chimney crosses a floor/ceiling line more than 6 ft above grade, install anchorage: two 3/16 in × 1 in straps, embed each 12 in into the chimney, hook them around the outer bars and extend 6 in beyond the bend. Fasten each strap to not less than four joists using two 1/2‑inch bolts. (§§ R1001.4, R1001.4.1)

Step 4 — Grouting:

  • Grout the cells/wythes per Section R606 rules, but do not let grout bond to the flue liner so the liner remains free to expand/contract. (§ R1001.3.1)

This configuration meets the prescriptive CRC requirements cited above (vertical steel, horizontal ties, and anchorage details) for SD D1 chimneys of this width.

Related provisions

  • § R1001.3 — Seismic reinforcing applicability for masonry fireplaces and chimneys (primary controlling section)
  • § R1001.3.1 — Vertical reinforcing: number/size/placement of vertical bars (primary controlling section)
  • § R1001.3.2 — Horizontal reinforcing / tie spacing and ties at bends
  • § R1001.4 — Seismic anchorage trigger and general anchorage requirement (anchorage at floor/ceiling/roof lines > 6 ft)
  • § R1001.4.1 — Anchorage strap size, embedment, hook and fastening details
  • Table R1001.1 — Summary table of many fireplace/chimney requirements (useful quick reference)

Code references

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

  • CRC § 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

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    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.

  • CRC § 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.

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    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.

  • CRC § 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 A —MASONRY FIREPLACES

    2111 A .1 General. The construction of masonry fireplaces, consisting of concrete or masonry, shall be in accordance with this section.

    2111 A .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 A .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

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    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 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.

  • CRC § 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.
  • CRC § 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.

  • CRC § 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.

  • CRC § 3.2 High relevance — show source text

    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. Where cold-formed steel framing is used, the location where the [1] / 2 -inch (12.7 mm) bolts are used to attach the straps to the framing shall be reinforced with not less than a 3-inch × 3-inch × 0.229-inch (76 mm × 76 mm × 5.8 mm) steel plate on top of a strap that is screwed to the framing with not fewer than seven No. 6 screws for each bolt.

    R1003.5 Corbeling. Masonry chimneys shall not be corbeled more than one-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) thick 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 shall be permitted to be equal to 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.

    R1003.6 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.

    R1003.7 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 R1003.5.

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  • CRC § 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.
  • CRC § 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.

  • CRC § 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.

  • CRC § 10-6 High relevance — show source text

    internal heat exchange channels in which the flow path downstream of the firebox includes flow in a horizontal or downward direction before entering the chimney and that delivers heat by radiation from the masonry surface of the heater.

    R1002.2 Installation. Masonry heaters shall be installed in accordance with this section and comply with one of the following:

    1. Masonry heaters shall comply with the requirements of ASTM E1602.
    2. Masonry heaters shall be listed and labeled in accordance with UL 1482 or CEN 15250 and installed in accordance with the manufacturer’s instructions.

    R1002.3 Footings and foundation. The firebox floor of a masonry heater shall be a minimum thickness of 4 inches (102 mm) of noncombustible material and be supported on a noncombustible footing and foundation in accordance with Section R1003.2.

    10-6 2025 CALIFORNIA RESIDENTIAL CODE

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

    CHIMNEYS AND FIREPLACES

    R1002.4 Seismic reinforcing. In Seismic Design Categories D 0, D 1 and D 2, masonry heaters shall be anchored to the masonry foundation in accordance with Section R1003.3. Seismic reinforcing shall not be required within the body of a masonry heater whose height is equal to or less than 3.5 times its body width and where the masonry chimney serving the heater is not 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 R1003.

    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.

Frequently asked questions

Do these reinforcing and anchorage requirements apply in Seismic Design Category A or B?

No. Reinforcement and seismic anchorage are not required in Seismic Design Category A or B; the requirements apply beginning in Category C per § R1001.3 .

How many vertical bars do I need for a 90‑inch‑wide chimney?

Start with 4 × No. 4 for the first 40 inches, then add 2 × No. 4 for each additional 40‑inch increment or fraction. For 90 in: 40 in → 4 bars; remaining 50 in is another increment → +2; total = 6 × No. 4 (because 90 in is >80 in but less than 120 in would require more — check increments carefully against § R1001.3.1) .

When must I anchor the chimney to the framing?

Anchor at every floor, ceiling or roof line that is more than 6 feet above grade, unless the chimney is completely within exterior walls. See § R1001.4 and § R1001.4.1 for strap and fastening details .

Can grout bond to the flue liner?

No — grout shall be prevented from bonding with the flue liner so the liner is free to move with thermal expansion (see § R1001.3.1) .

What is a “No. 4” bar?

“No. 4” is the reinforcing bar designation used in the code (nominal 1/2‑inch diameter). The CRC specifies the use of No. 4 vertical bars in § R1001.3.1 .

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Masonry Fireplaces

California Residential Code