CRC · California Residential Code

What are the required chimney wall thickness, crickets and fireblocking where chimneys pass through roofs and floors?

A homeowner can expect that masonry chimneys must have walls at least 4 inches thick, crickets (small saddle roofs) are required behind wide chimneys (greater than 30 inches parallel to the ridge) and their height is set by a table tied to roof slope, and any place a chimney passes through a floor, ceiling or roof must be fireblocked with noncombustible material (self‑supporting or metal‑supported where next to wood framing) — see **§ R1003.10**, **§ R1003.20**, and **§ R1003.19**.

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Last reviewed: July 6, 2026

What the code requires — plain English

The California Residential Code requires masonry chimney walls to have a minimum nominal thickness of 4 inches (see § R1003.10). Where a chimney is more than 30 inches (762 mm) wide measured parallel to the ridgeline and does not intersect the ridgeline, a cricket (saddle) is required and its height is set by Table § R1003.20. All spaces where chimneys pass through floors, ceilings or roofs must be fireblocked with noncombustible material; where the space is between the chimney and wood joists, beams or headers the fireblocking must be self‑supporting or supported on metal strips/metal lath (see § R1003.19).

Most important rule: Chimney walls must be at least 4 in. thick, chimneys wider than 30 in. (parallel to the ridge) that don’t intersect the ridge must have a cricket sized per § R1003.20, and every roof/floor penetration around a chimney must be fireblocked with noncombustible material per § R1003.19.

Requirements in detail

Chimney wall thickness (masonry chimneys)

  • Minimum nominal thickness: 4 inches (102 mm) for masonry chimney walls constructed of concrete, solid masonry units or hollow masonry units grouted solid, i.e., the chimney wall itself must be at least 4 in. thick. This is the requirement tied to § R1003.10 (see also the summary table for masonry chimneys).

Crickets (saddles) behind chimneys on roofs

  • Cricket required when the dimension parallel to the ridgeline is greater than 30 inches (762 mm) and the chimney does not intersect the ridgeline. The cricket intersection must be flashed and counter‑flashed like a regular roof‑to‑chimney detail. See § R1003.20.
  • Cricket height (H) is specified as a fraction of the chimney/saddle width (W) depending on roof slope — use Table § R1003.20 (values reproduced below).
  • Note: the roof chapter also requires crickets/saddles on ridge side of penetrations greater than 30 in. measured perpendicular to the slope; skylight exception applies per roof flashing rules (see roof flashing rules).

Decision‑relevant dimensions/values (from Table R1003.20 and related rules)

Decision / dimension Required value Code Reference
Minimum masonry chimney wall thickness 4 in. (102 mm) nominal § R1003.10
Cricket required when parallel-to-ridge dimension > 30 in. (762 mm) and chimney does not intersect ridge Yes — cricket required; must be flashed/counterflashed § R1003.20
Cricket height H by roof slope (H = fraction of W) See table below § R1003.20
Fireblocking at roof/floor/ceiling penetrations around chimneys Noncombustible material, securely fastened; where adjacent to wood joists/beams/headers, fireblocking must be self‑supporting or placed on metal strips/metal lath § R1003.19

Cricket height table (Table R1003.20)

Roof slope H (cricket height)
12:12 1/2 of W
8:12 1/3 of W
6:12 1/4 of W
4:12 1/6 of W
3:12 1/8 of W
(Where W = width of chimney or penetration as used by the table.)

Fireblocking where chimneys pass through floors/ceilings/roofs

  • All spaces between chimneys and the floors or ceilings they pass through must be fireblocked with noncombustible material securely fastened in place; do not leave annular spaces open. For spaces between chimneys and wood joists/beams/headers the fireblocking must be self‑supporting or placed on metal strips or metal lath across the combustible framing, per § R1003.19.
  • Factory‑built chimneys/fireplaces have their own required fireblocking methods (see UL listings and the mechanical/manufacturer instructions).

Exceptions & special cases

  • The residential roof flashing chapter contains an exception for some unit skylights (skylights installed per their manufacturer instructions may be permitted without a cricket) — see § R903.2.2 for that roof‑flashing exception. That same roof section also prescribes minimum metal flashing thickness and acceptable covers for crickets.
  • Some masonry chimney clearance exceptions (allowing combustibles closer to chimney exterior) exist where a listed lining system is used or where the chimney is part of a masonry or concrete wall; those are separate clearance/exception provisions in the masonry chapters and are not a substitute for the fireblocking requirement where chimneys pass through floors/ceilings. If you need specific clearance exceptions, those are in the masonry/chimney clearance text.
  • Where a masonry chimney is used as veneer over a framed chimney, through‑flashing and weep holes are required (see the masonry material/veneer note tied to wall thickness).

Common mistakes

  • Assuming a cricket is required any time a chimney is wide — the code requires a cricket only when the dimension parallel to the ridge is greater than 30 in. and the chimney does not intersect the ridge (§ R1003.20).
  • Using combustible materials to fireblock the annular space around a chimney penetration — fireblocking must be noncombustible and properly supported where adjacent to wood framing (§ R1003.19).
  • Filling the required airspace around a masonry chimney with insulation or other materials — the code prohibits filling the clearance airspace except as required to provide fireblocking per the chimney/fireblocking provisions (see masonry clearance/airspace rules).
  • Forgetting to flash and counter‑flash the intersection of the cricket and chimney: the code requires the cricket‑chimney intersection be flashed/counter‑flashed the same as normal roof‑chimney intersections (§ R1003.20).

Worked example — apply the rules with numbers

Scenario: A masonry chimney with outside width (parallel to the ridge) W = 36 inches, roof slope = 6:12, the chimney passes through the attic floor and roof (does not intersect the ridge).

  1. Wall thickness: The masonry chimney wall must be at least 4 in. nominal thickness (per § R1003.10). Confirm materials are concrete, solid masonry units or hollow units grouted solid.
  2. Cricket: Since the parallel‑to‑ridge dimension is 36 in. (> 30 in.) and the chimney does not intersect the ridge, a cricket is required per § R1003.20. For a 6:12 slope Table § R1003.20 requires H = 1/4 of W. With W = 36 in., H = 36 × 1/4 = 9 inches. The cricket/chimney junction must be flashed and counter‑flashed per the same section.
  3. Fireblocking at floor/ceiling: Where the chimney passes through the attic floor/ceiling, all spaces between the chimney and the floor/ceiling must be fireblocked with noncombustible material securely fastened. If the chimney opening is framed with wood joists or headers, the fireblocking must be self‑supporting or supported on metal strips/metal lath as required by § R1003.19.

Related provisions (code sections to consult)

  • § R1003.10 — Chimney wall thickness (masonry) — minimum 4 in. nominal.
  • § R1003.19 — Chimney fireblocking: noncombustible, self‑supporting or metal‑supported where adjacent to wood framing.
  • § R1003.20 — Chimney crickets: when required and cricket dimensions (table).
  • § R1003.6 — Prohibits changes in chimney/flue size or shape within 6 in. above/below floor/ceiling/roof penetrations (important when detailing reductions/offsets at penetrations).
  • § R302.11 — General fireblocking requirements for combustible construction (chimney fireblocking cross‑reference).
  • § R903.2.2 — Roof crickets/saddles and flashing requirements (roof chapter crossover).

If you want, I can: draw a scaled sketch showing the cricket dimensions for a given W and roof slope, or prepare a short checklist you can hand the contractor to verify compliance on site.

Code references

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

  • California Residential Code High relevance — show source text

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    R1003.19 Chimney fireblocking. Spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between chimneys and wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible

    material and the chimney.
    R1003.20 Chimney crickets. Chimneys shall be provided with crickets where the dimension parallel to the ridgeline is greater than
    30 inches (762 mm) and does not intersect the ridgeline. The intersection of the cricket and the chimney shall be flashed and counter-
    flashed in the same manner as normal roof-chimney intersections. Crickets shall be constructed in compliance with Figure R1003.20
    and Table R1003.20.    		 Col2
    TABLE R1003.20—CRICKET DIMENSIONS TABLE R1003.20—CRICKET DIMENSIONS
    ** ROOF SLOPE** ** H**
    12:12 1/2 of W
    8:12 1/3 of W
    6:12 1/4 of W
    4:12 1/6 of W
    3:12 1/8 of W

    FIGURE R1003.20—CHIMNEY CRICKET

    AIRSPACE

    ROOF LINE

  • CRC § 25.4 High relevance — show source text

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    R1003.19 Chimney fireblocking. Spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between chimneys and wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible

    material and the chimney.
    R1003.20 Chimney crickets. Chimneys shall be provided with crickets where the dimension parallel to the ridgeline is greater than
    30 inches (762 mm) and does not intersect the ridgeline. The intersection of the cricket and the chimney shall be flashed and counter-
    flashed in the same manner as normal roof-chimney intersections. Crickets shall be constructed in compliance with Figure R1003.20
    and Table R1003.20.    		 Col2
    TABLE R1003.20—CRICKET DIMENSIONS TABLE R1003.20—CRICKET DIMENSIONS
    ** ROOF SLOPE** ** H**
    12:12 1/2 of W
    8:12 1/3 of W
    6:12 1/4 of W
    4:12 1/6 of W
    3:12 1/8 of W

    FIGURE R1003.20—CHIMNEY CRICKET

    AIRSPACE

    ROOF LINE

    For SI: 1 inch = 25.4 mm.

    FLUE LINER Col2 Col3 Col4 Col5
    1 IN.
    AIRS    		 1 IN.
    AIRS    		 1 IN.
    AIRS    		 1 IN.
    AIRS    		 1 IN.
    AIRS
    W W W W W

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    �

    CHIMNEYS AND FIREPLACES

    SECTION R1004—FACTORY-BUILT FIREPLACES

    R1004.1 General. Factory-built fireplaces shall be listed and labeled and shall be installed in accordance with the conditions of the listing. Factory-built fireplaces shall be tested in accordance with UL 127.

    R1004.1.1 Factory-built wood burning fireplaces. Factory-built wood burning fireplaces shall be qualified at the U.S. EPA’s Volun- tary Fireplace Program Phase 2 emissions level and be in accordance with the California Green Building Standards Code, Chapter 4, Division 4.5.

    R1004.2 Hearth extensions. Hearth extensions of approved factory-built fireplaces shall be installed in accordance with the listing of the fireplace. The hearth extension shall be readily distinguishable from the surrounding floor area. Listed and labeled hearth extensions shall comply with UL 1618.

  • CRC § 9.1 High relevance — show source text

    Defined R202 Chimneys Caps R1003.9.1 Clearance R1003.18 Corbeling R1003.5 Crickets R1003.20 Design (masonry) R1003.1 Factory-built R1005 Fireblocking R1003.19 Fireplaces Chapter 10 Flue area R1003.14, R1003.15 Flue lining R1003.11 Load R1003.8 Multiple flue R1003.14 Rain caps R1003.9.3 Spark arrestors R1003.9.2 Termination R1003.9

    Wall thickness R1003.10

    Clay Tiles R905.3

    Cleanout Masonry chimney R1003.17 Climate Types R301.2 Climate Zones R202, R702.7.3, Table R702.7(5) Columns R407

    2025 CALIFORNIA RESIDENTIAL CODE INDEX-1

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    INDEX

    Live load R301.5

    Nominal sizes R301.8

    Roof load R301.6

    Seismic R301.2.2

    Snow loads R301.2.3 Story height R301.3 Sunrooms R301.2.1.1.1

    Wind R301.2.1

    Doors

    Egress R318.2 Exterior R318.3, R609 Glazing R324 Draftstopping R302.12, R502.13 Drainage Foundation R405 Site drainage R300 Ducts

    Defined R202 Dwelling-garage wall and ceiling penetration R302.5.2 System, definition R202 Dwelling Unit Separation R302.2, R302.3 Sprinklers (see Automatic Sprinkler System)

    Electric Vehicle Charging Stations R317.6 Elevator R323.1, R323.3 Emergency Escape and Rescue Openings R319

    Additions R319.6

    Area wells R319.4 Bars, grilles, covers and screens R319.4.4

    Basements, existing R319.7 Dimensions R319.2

    Doors R319.3

    Replacement window R319.5 Under decks and porches R319.2.4 Where required R319.1 Window fall protection R321.2 Emergency Housing Appendix CJ Energy Storage Systems R328 ESS vehicle impact protection Figure R330.8.1 Maximum aggregate ratings of ESS Table R330.5 Protection from impact R330.8 Toxic and highly toxic gas R330.12 Entry 1.8.5, R104.4 Existing Buildings Appendix BO Administrative R101.2, R102.6, R105.1, R105.8, R106.2, R113.1, R113.2 Basements R313.1.2, R319.7 Carbon monoxide alarms R311.2.2, R311.5, R311.6 Flood R104.3.1

  • CRC § 21A-17 High relevance — show source text

    Exceptions:

    1. Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777, and installed in accordance with the manufacturer’s instructions, are permitted to have combustible material in contact with their exterior surfaces.

    2. Where masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 12 inches (305 mm) from the inside surface of the nearest flue lining.

    3. Exposed combustible trim and the edges of sheathing materials, such as wood siding, are permitted to abut the masonry chimney sidewalls, in accordance with Figure 2113 A .19, provided that such combustible trim or sheathing is not less than 12 inches (305 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm).

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    MASONRY

    FIGURE 2113 A .19—ILLUSTRATION OF EXCEPTION THREE CHIMNEY CLEARANCE PROVISION

    MASONRY ABUTTING

    COMBUSTIBLE SHEATHING

    12" FROM FLUE LINING

    Col1 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 M
    C
    12

    1" CLEARANCE (AIRSPACE) TO COMBUSTIBLE SHEATHING

    2113 A .20 Chimney fireblocking. All spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.

    SECTION 2114 A —DRY-STACK MASONRY

    2114 A .1 General. The design of dry-stack masonry structures shall comply with the requirements of Chapters 1 through 8 of TMS 402 except as modified by Sections 2114 A .2 through 2114 A .5.

    2114 A .2 Limitations. Dry-stack masonry shall be prohibited in Risk Category IV structures.

    2114 A .3 Materials. Concrete masonry units complying with ASTM C90 shall be used.

    2114 A .4 Strength. Dry-stack masonry shall be of adequate strength and proportions to support all superimposed loads without exceeding the allowable stresses listed in Table 2114 A .4. Allowable stresses not specified in Table 2114 A .4 shall comply with the requirements of Chapter 8 of TMS 402.

  • CRC § 2.1 High relevance — show source text

    R903.2.1 Locations. Flashings shall be installed at wall and roof intersections, wherever there is a change in roof slope or direction and around roof openings. A flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall. Where flashing is of metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inch (0.5 mm) (No. 26 galvanized sheet).

    R903.2.2 Crickets and saddles. A cricket or saddle shall be installed on the ridge side of any chimney or penetration more than 30 inches (762 mm) wide as measured perpendicular to the slope. Cricket or saddle coverings shall be sheet metal or of the same material as the roof covering.

    Exception: Unit skylights installed in accordance with Section R324.6 and flashed in accordance with the manufacturer’s instructions shall be permitted to be installed without a cricket or saddle.

    R903.3 Coping. Parapet walls shall be properly coped with noncombustible, weatherproof materials of a width not less than the thickness of the parapet wall.

    R903.4 Roof drainage. Unless roofs are sloped to drain over roof edges, roof drains shall be installed at each low point of the roof.

    R903.4.1 Secondary (emergency overflow) drains or scuppers. Where roof drains are required, secondary emergency overflow roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason. Overflow drains having the same size as the roof drains shall be installed with the inlet flow line located 2 inches (51 mm) above the low point of the roof, or overflow scuppers having three times the size of the roof drains and having a minimum opening height of 4 inches (102 mm) shall be installed in the adjacent parapet walls with the inlet flow located 2 inches (51 mm) above the low point of the roof served. The installation and sizing of overflow drains, leaders and conductors shall comply with the California Plumbing Code .

    SECTION R904—MATERIALS

    R904.1 Scope. The requirements set forth in this section shall apply to the application of roof covering materials specified herein. Roof assemblies shall be applied in accordance with this chapter and the manufacturer’s installation instructions. Installation of roof assemblies shall comply with the applicable provisions of Section R905.

    R904.2 Compatibility of materials. Roof assemblies shall be of materials that are compatible with each other and with the building or structure to which the materials are applied.

    R904.3 Material specifications and physical characteristics. Roof covering materials shall conform to the applicable standards listed in this chapter.

    R904.4 Product identification. Roof covering materials shall be delivered in packages bearing the manufacturer’s identifying marks and approved testing agency labels required. Bulk shipments of materials shall be accompanied by the same information issued in the form of a certificate or on a bill of lading by the manufacturer.

    SECTION R905—REQUIREMENTS FOR ROOF COVERINGS

    R905.1 Roof covering application. Roof coverings shall be applied in accordance with the applicable provisions of this section and the manufacturer’s installation instructions. Unless otherwise specified in this section, roof coverings shall be installed to resist the component and cladding loads specified in Table R301.2.1(1), adjusted for height and exposure in accordance with Table R301.2.1(2).

  • CRC § 7.1 Medium relevance — show source text

    Covering R703 Insulation finish systems R703.9 Lath R703.7.1

    Plaster R703.7 Exterior Insulation and Finish Systems (EIFS) 703.9

    Exterior Wall

    Construction R302.1

    Fire-resistance rating R302.1

    Factory Built Chimneys R1005 Fireplace stoves R1005.3 Fireplaces R1004 Fastening Table R602.3(1) Fees, Permit R108 Finishes Flame spread and smoke density R302.9 For ceilings R805 Interior R302.9, R311, R702 Fire Sprinkler System (see Automatic Sprinkler System) Ceiling configurations R309.3.4.1.1, R309.3.4.1.2, R309.3.4.1.3 Flow rate R309.3.4.1 Fireblocking Barrier between stories R302.11,

    R602.8 Chimney R1003.19 Fireplace R1001.12 Fireplaces Chapter 10 Clearance R1001.11 Corbeling R1001.8 Factory-built R1004 Fireblocking R1001.12 Walls R1001.5

    Fire-Resistant Construction R302 Draftstopping R302.2 Dwelling-garage fire separation R302.6 Dwelling-garage opening and penetration R302.5 Exterior walls R302.1 Fireblocking R302.11 Floors R302.13

    Foam plastics R302.8 Insulation R302.10, R302.14 Penetrations R302.4

    Townhouse separation R302.2 Two-family dwellings R302.3 Under-stair protection R302.7 Wall and ceiling finishes R302.9 Fire-Separation Distance Exterior walls and wall projections R302.1 Ground-mounted photovoltaic systems R329.7, R329.8 Fixtures

    Clearance R327.1

    Flood protection R306.1.6 Plumbing fixture, general R326, R327 Flame Spread Index R302.10, R302.9 Flashing R703.4, R703.8.5, R903.2, R905 Flood Protection Plan Areas protected by the facilities of Central Valley Appendix CK Flood-Resistant Construction

    General and structural R301.2.4, R306 Floors

    Bathtub and shower R327.2 Concrete (on ground) R506 Loads R301, R501.2 Steel framing R505 Treated wood (on ground) R504

    Wood framing R502 Flue

    Area R1003.14, R1003.15 Lining R1003.11, R1003.12 Multiple R1003.13 Foam Plastics R303 Footings R403 Foundations Chapter 4 Cripple walls R602.10.9, R602.11.2, R602.9

    Frost protection R403.1.4.1 Inspection R109.1.1 Walls R404

    Frame

  • CRC § 1.2. Medium relevance — show source text

    1.2. By a horizontal distance of not less than the depth of the wall cavity where the wall cavity is filled with cellulose loose-fill, rockwool or slag mineral wool insulation. 1.3. By solid fireblocking in accordance with Section R302.11. 1.4. By protecting both boxes with listed putty pads. 1.5. By other listed materials and methods. 2. Membrane penetrations by listed electrical boxes of any materials provided that the boxes have been tested for use in fire-resistance-rated assemblies and are installed in accordance with the instructions included in the listing. The annular space between the wall membrane and the box shall not exceed [1] / 8 inch (3.1 mm) unless listed otherwise. Such boxes on opposite sides of the wall shall be separated by one of the following: 2.1. By the horizontal distance specified in the listing of the electrical boxes. 2.2. By solid fireblocking in accordance with Section R302.11. 2.3. By protecting both boxes with listed putty pads. 2.4. By other listed materials and methods. 3. The annular space created by the penetration of a fire sprinkler or water-filled fire sprinkler piping, provided that the annular space is covered by a metal escutcheon plate. 4. Ceiling membrane penetrations by listed luminaires or by luminaires protected with listed materials that have been tested for use in fire-resistance-rated assemblies and are installed in accordance with the instructions included in the listing.

    R302.5 Dwelling unit garage opening and penetration protection. Openings and penetrations through the walls or ceilings separating the dwelling unit from the garage shall be in accordance with Sections R302.5.1 through R302.5.3.

    R302.5.1 Opening protection. Openings from a private garage directly into a room used for sleeping purposes shall not be permitted. Other openings between the garage and dwelling unit shall be equipped with solid wood doors not less than 1 [3] / 8 inches (35 mm) in thickness, solid or honeycomb-core steel doors not less than 1 [3] / 8 inches (35 mm) thick, or 20-minute fire-rated doors. Doors shall be self-latching and equipped with a self-closing or automatic-closing device.

    Exception: Where the residence and the private garage are protected by an automatic residential fire sprinkler system in accor- dance with Sections R309 and R317.5.1, other door openings between the private garage and the residence need only be self- closing and self-latching. This exception shall not apply to rooms used for sleeping purposes.

    R302.5.2 Duct penetration. Ducts in the garage and ducts penetrating the walls or ceilings separating the dwelling unit from the garage shall be constructed of a minimum No. 26 gage (0.48 mm) sheet steel or other approved material and shall not have openings into the garage.

    R302.5.3 Other penetrations. Penetrations through the separation required in Section R302.6 shall be protected as required by Section R302.11, Item 4.

  • CRC § 2113.19 Medium relevance — show source text

    FIGURE 2113.19—ILLUSTRATION OF EXCEPTION THREE CHIMNEY CLEARANCE PROVISION

    MASONRY ABUTTING

    COMBUSTIBLE SHEATHING

    12" FROM FLUE LINING

    Col1 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 M
    C
    12

    1" CLEARANCE (AIRSPACE) TO COMBUSTIBLE SHEATHING

    2113.20 Chimney fireblocking. All spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.

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    MASONRY

    SECTION 2114—DRY-STACK MASONRY

    2114.1 General. The design of dry-stack masonry structures shall comply with the requirements of Chapters 1 through 8 of TMS 402 except as modified by Sections 2114.2 through 2114.5.

    2114.2 Limitations. Dry-stack masonry shall be prohibited in Risk Category IV structures.

    2114.3 Materials. Concrete masonry units complying with ASTM C90 shall be used.

    2114.4 Strength. Dry-stack masonry shall be of adequate strength and proportions to support all superimposed loads without exceeding the allowable stresses listed in Table 2114.4. Allowable stresses not specified in Table 2114.4 shall comply with the requirements of Chapter 8 of TMS 402.

    TABLE 2114.4—GROSS CROSS-SECTIONAL AREA ALLOWABLE STRESS FOR DRY-STACK MASONRY Col2
    DESCRIPTION MAXIMUM ALLOWABLE STRESS (psi)
    Compression 45
    Flexural tension
    Horizontal span
    Vertical span    		 30
    18
    Shear 10
    For SI: 1 pound per square inch = 0.006895 MPa. For SI: 1 pound per square inch = 0.006895 MPa.

    2114.5 Construction. Construction of dry-stack masonry shall comply with ASTM C946.

    SECTION 2115-ADDITIONAL REQUIREMENTS FOR COMMUNITY COLLEGES [DSA-SS/CC]

    2115.1 General. In addition to the provisions of this chapter, the following requirements shall apply to community college buildings regulated by the Division of the State Architect-Structural Safety/Community Colleges (DSA-SS/CC).

    2115.1.1 Prohibitions. The following design, systems and materials in TMS 402/602 are not permitted by DSA: 1. Unreinforced masonry. 2. Autoclaved aerated concrete (AAC) masonry. 3. Empirical design of masonry.

    4. Adobe construction.

  • CRC § 2113.6 Medium relevance — show source text

    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.

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

    MASONRY

    2113.9.1 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.

    2113.9.2 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. The net free area of the spark arrestor shall not be less than four times the net free area of the outlet of the chimney.
    2. The spark arrestor screen shall have heat and corrosion resistance equivalent to 12-gage wire, 19-gage galvanized steel or 24-gage stainless steel.
    3. Openings shall not permit the passage of spheres having a diameter greater than [1] / 2 inch (13 mm) nor block the passage of spheres having a diameter less than [3] / 8 inch (9.5 mm).
    4. The spark arrestor shall be accessible for cleaning and the screen or chimney cap shall be removable to allow for cleaning of the chimney flue.

    2113.9.3 Rain caps. Where a masonry or metal rain cap is installed on a masonry chimney, the net free area under the cap shall be not less than four times the net free area of the outlet of the chimney flue it serves.

    2113.10 Wall thickness. Masonry chimney walls shall be constructed of concrete, solid masonry units or hollow masonry units grouted solid with not less than 4 inches (102 mm) nominal thickness.

    2113.10.1 Masonry veneer chimneys. Where masonry is used as veneer for a framed chimney, through flashing and weep holes shall be provided as required by Chapter 14.

  • CRC § 718.2.5 Medium relevance — show source text

    718.2.5 Ceiling and floor openings. Where required by Section 712.1.8, Exception 1 of Section 714.5.1.2 or Section 714.6, fireblocking of the annular space around vents, pipes, ducts, chimneys and fireplaces at ceilings and floor levels shall be installed with a material specifically tested in the form and manner intended for use to demonstrate its ability to remain in place and resist the free passage of flame and the products of combustion.

    718.2.5.1 Factory-built chimneys and fireplaces. Factory-built chimneys and fireplaces shall be fireblocked in accordance with UL 103 and UL 127.

    718.2.6 Exterior wall coverings. Fireblocking shall be installed within concealed spaces of exterior wall coverings and other exterior architectural elements where permitted to be of combustible construction as specified in Section 1405 or where erected with combustible frames. Fireblocking shall be installed at maximum intervals of 20 feet (6096 mm) in either dimension so that there will be no concealed space exceeding 100 square feet (9.3 m [2] ) between fireblocking. Where wood furring strips are used, they shall be of approved wood of natural decay resistance or preservative-treated wood. If noncontinuous, such elements shall have closed ends, with not less than 4 inches (102 mm) of separation between sections.

    Exceptions:

    1. Fireblocking of cornices is not required in single-family dwellings. Fireblocking of cornices of a two-family dwelling is required only at the line of dwelling unit separation.
    2. Fireblocking shall not be required where the exterior wall covering is installed on noncombustible framing and the face of the exterior wall covering exposed to the concealed space is covered by one of the following materials: 2.1. Aluminum having a minimum thickness of 0.019 inch (0.5 mm). 2.2. Corrosion-resistant steel having a base metal thickness not less than 0.016 inch (0.4 mm) at any point. 2.3. Other approved noncombustible materials.
    3. Fireblocking shall not be required where the exterior wall covering has been tested in accordance with, and complies with the acceptance criteria of, NFPA 285. The exterior wall covering shall be installed as tested in accordance with NFPA 285.

    718.2.7 Concealed sleeper spaces. Where wood sleepers are used for laying wood flooring on masonry or concrete fire-resistance-rated floors, the space between the floor slab and the underside of the wood flooring shall be filled with an approved material to resist the free passage of flame and products of combustion or fireblocked in such a manner that open spaces under the flooring shall not exceed 100 square feet (9.3 m [2] ) in area and such space shall be filled solidly under permanent partitions so that communication under the flooring between adjoining rooms shall not occur.

    Exceptions:

    1. Fireblocking is not required for slab-on-grade floors in gymnasiums.
    2. Fireblocking is required only at the juncture of each alternate lane and at the ends of each lane in a bowling facility.

    718.3 Draftstops in floors. Draftstops shall be installed to subdivide floor/ceiling assemblies where required by Section 708.4.3. In other than Group R occupancies, draftstops shall be installed to subdivide combustible floor/ceiling assemblies so that horizontal floor areas do not exceed 1,000 square feet (93 m [2] ).

  • CRC § 10.4 Medium relevance — show source text

    R302.10.4 Exposed attic insulation. Exposed insulation materials installed on attic floors shall have a critical radiant flux of not less than 0.12 watt per square centimeter when tested in accordance with ASTM E970.

    R302.11 Fireblocking. In combustible construction, fireblocking shall be provided to cut off both vertical and horizontal concealed draft openings and to form an effective fire barrier between stories, and between a top story and the roof space.

    Fireblocking shall be provided in wood-framed construction in the following locations:

    1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs, as follows:

    1.1. Vertically at the ceiling and floor levels. 1.2. Horizontally at intervals not exceeding 10 feet (3048 mm). 2. At interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings. 3. In concealed spaces between stair stringers at the top and bottom of the run. Enclosed spaces under stairs shall comply with Section R302.7.

    1. At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion. The material filling this annular space shall not be required to meet the ASTM E136 requirements.
    2. For the fireblocking of chimneys and fireplaces, see Section R1003.19.
    3. Fireblocking of cornices of a two-family dwelling is required at the line of dwelling unit separation.

    R302.11.1 Fireblocking materials. Except as provided in Section R302.11, Item 4, fireblocking shall consist of the following materials.

    1. Two-inch (51 mm) nominal lumber.
    2. Two thicknesses of 1-inch (25.4 mm) nominal lumber with broken lap joints.
    3. One thickness of [23] / 32 -inch (18.3 mm) wood structural panels with joints backed by [23] / 32 -inch (18.3 mm) wood structural panels.
    4. One thickness of [3] / 4 -inch (19.1 mm) particleboard with joints backed by [3] / 4 -inch (19.1 mm) particleboard.
    5. One-half-inch (12.7 mm) gypsum board.
    6. One-quarter-inch (6.4 mm) cement-based millboard.
    7. Batts or blankets of mineral wool or glass fiber or other approved materials installed in such a manner as to be securely retained in place.
    8. Cellulose insulation installed as tested in accordance with ASTM E119 or UL 263, for the specific application.

    R302.11.1.1 Batts or blankets of mineral or glass fiber. Batts or blankets of mineral or glass fiber or other approved nonrigid materials shall be permitted for compliance with the 10-foot (3048 mm) horizontal fireblocking in walls constructed using parallel rows of studs or staggered studs.

    R302.11.1.2 Unfaced fiberglass. Unfaced fiberglass batt insulation used as fireblocking shall fill the entire cross section of the wall cavity to a height of not less than 16 inches (406 mm) measured vertically. Where piping, conduit or similar obstructions are encountered, the insulation shall be packed tightly around the obstruction.

    R302.11.1.3 Loose-fill insulation material. Loose-fill insulation material shall not be used as a fireblock unless specifically tested in the form and manner intended for use to demonstrate its ability to remain in place and to retard the spread of fire and hot gases.

  • CRC § 2113.17 Medium relevance — show source text

    2113.17 Inlet. Inlets to masonry chimneys shall enter from the side. Inlets shall have a thimble of fireclay, rigid refractory material or metal that will prevent the connector from pulling out of the inlet or from extending beyond the wall of the liner.

    2113.18 Masonry chimney cleanout openings. Cleanout openings shall be provided within 6 inches (152 mm) of the base of each flue within every masonry chimney. The upper edge of the cleanout shall be located not less than 6 inches (152 mm) below the lowest chimney inlet opening. The height of the opening shall be not less than 6 inches (152 mm). The cleanout shall be provided with a noncombustible cover.

    Exception: Chimney flues serving masonry fireplaces, where cleaning is possible through the fireplace opening.

    2113.19 Chimney clearances. Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm). Chimneys located entirely outside the exterior walls of the building, including chimneys that pass through the soffit or cornice, shall have a minimum airspace clearance of 1 inch (25 mm). The airspace shall not be filled, except to provide fireblocking in accordance with Section 2113.20.

    Exceptions:

    1. Masonry chimneys equipped with a chimney lining system listed and labeled for use in chimneys in contact with combustibles in accordance with UL 1777, and installed in accordance with the manufacturer’s instructions, are permitted to have combustible material in contact with their exterior surfaces.

    2. Where masonry chimneys are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete wall less than 12 inches (305 mm) from the inside surface of the nearest flue lining.

    3. Exposed combustible trim and the edges of sheathing materials, such as wood siding, are permitted to abut the masonry chimney sidewalls, in accordance with Figure 2113.19, provided that such combustible trim or sheathing is not less than 12 inches (305 mm) from the inside surface of the nearest flue lining. Combustible material and trim shall not overlap the corners of the chimney by more than 1 inch (25 mm).

    FIGURE 2113.19—ILLUSTRATION OF EXCEPTION THREE CHIMNEY CLEARANCE PROVISION

    MASONRY ABUTTING

    COMBUSTIBLE SHEATHING

    12" FROM FLUE LINING

    Col1 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 M
    C
    12

    1" CLEARANCE (AIRSPACE) TO COMBUSTIBLE SHEATHING

    2113.20 Chimney fireblocking. All spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.

    21-18 2025 CALIFORNIA BUILDING CODE

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

  • CRC § 1.2 Medium relevance — show source text

    Room, minimum R312 Sleeping lofts R315.1, R315.2, R315.4 Area Wells R319.4

    INDEX

    Attic

    Access R807

    Habitable R316 Height R313.1.2 Ventilation R806 Automatic Sprinkler Systems R101.2, R309 Automotive Lifts R317.7

    Backfill

    Placement R404.1.7, R404.2.3, R404.2.4, R406.3.3, R406.3.4

    Basements

    Alterations R319.7 Ceiling height R313 Egress R318.4 Emergency escape and rescue openings R319.6 Bathroom R313.1, R326, R327 Exhaust fan R325.2.1

    Bathtub R326.1, R327 Enclosure R324.3.1, R324.4.5, R325.2 Finish R327.2 Space required R327.1 Board of Appeals (see Means of Appeal) Building Official Duties and powers R104 Built-Up Roofing (see Roofing)

    Carbon Monoxide Alarms R311

    Care Facilities R101.2, R322.3 Carports R317.2, R317.3 Ceiling Finishes R302.9, R805 Height R313 Certificate of Occupancy R110 Change of Occupancy R110.1 Emergency escape and rescue openings R319.5, R319.7.1 Chases R606.8

    Child Care

    Defined R202 Chimneys Caps R1003.9.1 Clearance R1003.18 Corbeling R1003.5 Crickets R1003.20 Design (masonry) R1003.1 Factory-built R1005 Fireblocking R1003.19 Fireplaces Chapter 10 Flue area R1003.14, R1003.15 Flue lining R1003.11 Load R1003.8 Multiple flue R1003.14 Rain caps R1003.9.3 Spark arrestors R1003.9.2 Termination R1003.9

    Wall thickness R1003.10

    Clay Tiles R905.3

    Cleanout Masonry chimney R1003.17 Climate Types R301.2 Climate Zones R202, R702.7.3, Table R702.7(5) Columns R407

    2025 CALIFORNIA RESIDENTIAL CODE INDEX-1

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

    INDEX

    Live load R301.5

    Nominal sizes R301.8

    Roof load R301.6

    Seismic R301.2.2

    Snow loads R301.2.3 Story height R301.3 Sunrooms R301.2.1.1.1

    Wind R301.2.1

    Doors

    Egress R318.2 Exterior R318.3, R609 Glazing R324 Draftstopping R302.12, R502.13 Drainage Foundation R405 Site drainage R300 Ducts

  • CRC § 10-7 Medium relevance — show source text

    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.

    2025 CALIFORNIA RESIDENTIAL CODE 10-7

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

    CHIMNEYS AND FIREPLACES

    R1003.8 Additional load. Chimneys shall not support loads other than their own weight unless they are designed and constructed to support the additional load. Construction of masonry chimneys as part of the masonry walls or reinforced concrete walls of the building shall be permitted.

    R1003.9 Termination. Chimneys shall extend not less than 2 feet (610 mm) higher than any portion of a 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.

    R1003.9.1 Chimney caps. Masonry chimneys shall have a concrete, metal or stone cap, a drip edge and a caulked bond break around any flue liners in accordance with ASTM C1283. The concrete, metal or stone cap shall be sloped to shed water.

    R1003.9.2 Spark arrestors. All chimneys attached to any appliance or fireplace that burns solid fuel shall be equipped with an approved spark arrester. Where a spark arrestor is installed on a masonry chimney, the spark arrestor shall meet all of the following requirements:

    1. The net free area of the arrestor shall be not less than four times the net free area of the outlet of the chimney flue it

    serves.

    1. The arrestor screen shall have heat and corrosion resistance equivalent to 12 gage wire, 19-gage galvanized steel or 24gage stainless steel.
    2. Openings shall not permit the passage of spheres having a diameter greater than [1] / 2 inch (12.7 mm) nor block the passage of spheres having a diameter less than [3] / 8 inch (9.5 mm).
    3. The spark arrestor shall be located with access for cleaning and the screen or chimney cap shall be removable to allow for cleaning of the chimney flue.
  • CRC § 4.8 Medium 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.

  • CRC § 25.4 Medium relevance — show source text

    SECTION R1001—MASONRY FIREPLACES

    R1001.1 General. Masonry fireplaces shall be constructed in accordance with this section and the applicable provisions of Chapters 3 and 4.

    TABLE R1001.1—SUMMARY OF REQUIREMENTS FOR MASONRY FIREPLACES AND CHIMNEYS Col2 Col3
    ** ITEM** ** LETTERa** ** REQUIREMENTS**
    Hearth slab thickness A 4 inches
    Hearth extension (each side of opening) B 8-inch fireplace opening < 6 square feet.
    12-inch fireplace opening ≥ 6 square feet.
    Hearth extension (front of opening) C 16-inch fireplace opening < 6 square feet.
    20-inch fireplace opening ≥ 6 square feet.
    Hearth slab reinforcing D Reinforced to carry its own weight and all imposed loads.
    Thickness of wall of firebox E 10-inch solid brick or 8 inches where a firebrick lining is used.
    Joints in firebrick1/4-inch maximum.
    Distance from top of opening to throat F 8 inches
    Smoke chamber wall thickness
    Unlined walls    		 G 6 inches
    8 inches
    Chimney
    Vertical reinforcingb    		 H Four No. 4 full-length bars for chimney up to 40 inches wide.
    Add two No. 4 bars for each additional 40 inches or fraction of
    width or each additional flue.
    Horizontal reinforcing J 1/4-inch ties at 18 inches and two ties at each bend in vertical steel.
    Bond beams K No specified requirements.
    Fireplace lintel L Noncombustible material.
    Chimney walls with flue lining M Solid masonry units or hollow masonry units grouted solid with not
    less than 4-inch nominal thickness.
    Distances between adjacent flues — See Section R1003.13.
    Effective flue area (based on area of fireplace opening) P See Section R1003.15.
    Clearances
    Combustible material
    Mantel and trim
    Above roof    		 R See Sections R1001.11 and R1003.18.
    See Section R1001.11, Exception 4.
    3 feet at roofline and 2 feet at 10 feet.
    Anchorageb
    Strap Number
    Embedment into chimney
    Fasten to
    Bolts    		 S 3/16-inch × 1-inch
    Two
    12 inches hooked around outer bar with 6-inch extension.
    4 joists
    Two1/2-inch diameter.
    Footing
    Thickness
    Width    		 T 12 inches min.
    6 inches each side of fireplace wall.
    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 square foot = 0.0929 m2.
    Note: This table provides a summary of major requirements for the construction of masonry chimneys and fireplaces. Letter references are to Figure R1001.1, which shows
    examples of typical construction. This table does not cover all requirements, nor does it cover all aspects of the indicated requirements. For the actual mandatory require-
    ments of the code, see the indicated section of text.
    a. The letters refer to Figure R1001.1.
    b.
  • CRC § 2113.3.2 Medium 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 § 9.1 Medium relevance — show source text

    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. The net free area of the spark arrestor shall not be less than four times the net free area of the outlet of the chimney.
    2. The spark arrestor screen shall have heat and corrosion resistance equivalent to 12-gage wire, 19-gage galvanized steel or 24-gage stainless steel.
    3. Openings shall not permit the passage of spheres having a diameter greater than [1] / 2 inch (13 mm) nor block the passage of spheres having a diameter less than [3] / 8 inch (9.5 mm).
    4. The spark arrestor shall be accessible for cleaning and the screen or chimney cap shall be removable to allow for cleaning of the chimney flue.

    2113 A .9.3 Rain caps. Where a masonry or metal rain cap is installed on a masonry chimney, the net free area under the cap shall be not less than four times the net free area of the outlet of the chimney flue it serves.

    2113 A .10 Wall thickness. Masonry chimney walls shall be constructed of concrete, solid masonry units or hollow masonry units grouted solid with not less than 4 inches (102 mm) nominal thickness.

    2113 A .10.1 Masonry veneer chimneys. Where masonry is used as veneer for a framed chimney, through flashing and weep holes shall be provided as required by Chapter 14.

    2113 A .11 Flue lining (material). Masonry chimneys shall be lined. The lining material shall be appropriate for the type of appliance connected, according to the terms of the appliance listing and the manufacturer’s instructions.

  • CRC § 0.019 Medium relevance — show source text
    DIAMETER OF CONNECTOR
    (inches)    		 MINIMUM THICKNESS
    (inches)

    Less than 6    		 0.019
    6 to less than 10 0.023


    10 to 12 inclusive    		 0.029


    14 to 16 inclusive    		 0.034

    Over 16
    		 0.056

    For SI units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m [2]

    802.10.1.4 Medium-Heat Appliances. Vent connectors for medium-heat appliances shall be constructed of factory-built, medium-heat chimney sections or steel of a thickness not less than that specified in Table 802.10.1.4 and shall comply with the following:

    (1) A steel vent connector for an appliance with a vent gas temperature in excess of 1000°F (538°C) measured at the entrance to the connector shall be lined with medium-duty fire brick or the equivalent.

    (2) The lining shall be at least 2 [1] ⁄ 2 inches (64 mm) thick for a vent connector having a diameter or greatest cross-sectional dimension of 18 inches (457 mm) or less. (3) The lining shall be at least 4 [1] ⁄ 2 inches (114 mm) thick laid on the 4 [1] ⁄ 2 inches (114 mm) bed for a vent connector having a diameter or greatest cross-sectional dimension greater than 18 inches (457 mm). (4) Where factory-built chimney sections are installed, they shall be joined together in accordance with the chimney manufacturer’s instructions. [NFPA 54:12.11.2.5]

    TABLE 802.10.1.4 MINIMUM THICKNESS FOR STEEL VENT CONNECTORS FOR MEDIUM-HEAT APPLIANCES [NFPA 54: TABLE 12.11.2.5] Col2 Col3

    VENT CONNECTOR SIZE
    VENT CONNECTOR SIZE
    VENT CONNECTOR SIZE


    DIAMETER
    (inches)    		 AREA
    (square inches)    		 MINIMUM THICKNESS
    (inches)


    Up to 14    		 Up to 154 0.053

    Over 14 to 16    		 154 to 201 0.067

    Over 16 to 18    		 201 to 254 0.093

    Over 18    		 Larger than 254 0.123

    For SI units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m [2]

    802.10.2 Size of Vent Connector. A vent connector for an appliance with a single draft hood or for a Category I fan-assisted combustion system appliance shall be sized and installed in accordance with Section 803.0 or engineering methods. [NFPA 54:12.11.3.1]

    For SI units: 1 inch = 25.4 mm, 1 square inch = 0.000645 m [2]

    2025 CALIFORNIA MECHANICAL CODE 161

    »

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    CHIMNEYS AND VENTS

  • CRC § 9-4 Medium relevance — show source text

    R904 Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4

    R905 Requirements for Roof Coverings . . . . . . . . . . . . . . . . 9-4

    R906 Roof Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19

    R907 Rooftop-Mounted Photovoltaic Panel Systems . . . 9-19

    R908 Reroofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19

    R909 Roof Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20

    CHAPTER 10 CHIMNEYS AND FIREPLACES . . . . . . . . . . . .10-3

    R1001 Masonry Fireplaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3

    R1002 Masonry Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-6

    R1003 Masonry Chimneys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-7

    R1004 Factory-Built Fireplaces. . . . . . . . . . . . . . . . . . . . . . . . 10-12

    R1005 Factory-Built Chimneys . . . . . . . . . . . . . . . . . . . . . . . . 10-12

    R1006 Exterior Air Supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-12

    Part IV—Energy Conservation. . . . . . . . . . . . . . . . . . . . . . . .11-1

    Part V—Mechanical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12-1

    Part VI—Fuel Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24-1

    Part VII—Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25-1

    Part VIII—Electrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34-1

    Part IX— Referenced Standards . . . . . . . . . . . . . . . . . . . . . .44-3

    CHAPTER 44 REFERENCED STANDARDS . . . . . . . . . . . . . .44-3

  • CRC § 10-6 Medium 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.

  • CRC § 8-7 Medium 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 § 8-3 Medium relevance — show source text

    R802 Wood Roof Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

    R803 Roof Sheathing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-30

    R804 Cold-Formed Steel Roof Framing . . . . . . . . . . . . . . . 8-31

    R805 Ceiling Finishes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-44

    R806 Roof Ventilation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-44

    R807 Attic Access. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-46

    CHAPTER 9 ROOF ASSEMBLIES . . . . . . . . . . . . . . . . . . . . . .9-3

    R901 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

    R902 Fire Classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

    R903 Weather Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4

    R904 Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4

    R905 Requirements for Roof Coverings . . . . . . . . . . . . . . . . 9-4

    R906 Roof Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19

    R907 Rooftop-Mounted Photovoltaic Panel Systems . . . 9-19

    R908 Reroofing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19

    R909 Roof Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20

    CHAPTER 10 CHIMNEYS AND FIREPLACES . . . . . . . . . . . .10-3

    R1001 Masonry Fireplaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3

    R1002 Masonry Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-6

    R1003 Masonry Chimneys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-7

Frequently asked questions

When exactly is a cricket required behind a chimney?

A cricket is required when the chimney dimension parallel to the ridgeline exceeds 30 inches (762 mm) and the chimney does not intersect the ridgeline; cricket size is then determined by Table § R1003.20.

How thick must a masonry chimney wall be?

Masonry chimney walls must be constructed of concrete, solid masonry units or hollow masonry units grouted solid with a minimum nominal thickness of 4 inches (102 mm) per § R1003.10.

What material is required for fireblocking around a chimney penetrations?

Fireblocking must be noncombustible material securely fastened in place. Where the space is between the chimney and wood joists/beams/headers the fireblocking must be self‑supporting or placed on metal strips or metal lath. See § R1003.19.

Can I fill the airspace around an exterior chimney with insulation?

No — the code prohibits filling the required chimney clearance airspace except where filling is done solely to provide required fireblocking per the chimney fireblocking provisions. Consult the chimney clearance text for specific limits.

Are there special requirements for factory‑built chimneys?

Yes — factory‑built chimneys and fireplaces must be installed per their listing and the manufacturer’s instructions and have specific tested fireblocking/clearance methods (see the factory‑built chimney/fireplace sections and applicable UL standards).

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California Residential Code