CRC · California Residential Code

What clearances and mantel/trim limitations apply to masonry fireplaces?

In plain terms: keep at least 2 inches of ventilated space between the front/sides of a masonry fireplace and any wood or other combustible material (4 inches at the back). Small wood trim can sometimes touch the masonry if it is placed far enough from the inside of the firebox; wooden mantels have minimum distances and projection limits (not within 6 inches of the opening; projection limited to 1/8" per inch of vertical distance within 12"). Always check **§ R1001.11**, Figure R1001.1 and any manufacturer listings before installing trim or a mantel.

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Last reviewed: July 6, 2026

What the code requires — plain English

Masonry fireplaces must keep a minimum airspace clearance to combustibles: 2 inches at the front and sides and 4 inches at the back of the fireplace, and that airspace must not be filled except with noncombustible material or approved fireblocking. These minimums are established by § R1001.11.

Special allowances and limits for combustible trim and mantels are spelled out as exceptions to that rule (distance‑to‑firebox requirements, where trim may abut, and projection limits for mantels) — see § R1001.11, Exceptions (3) & (4) and the illustration in Figure R1001.1 (Table R1001.1 cross‑references these details).

Keep at least 2" of clear, vented airspace between the faces/sides of a masonry fireplace and any combustible framing or materials (4" at the back) unless the installation meets one of the exceptions in § R1001.11.

Requirements in detail

Minimum clearances (airspace)

  • Front & sides: 2 inches (51 mm) minimum clearance to combustible wood members or materials. § R1001.11.
  • Back (rear face): 4 inches (102 mm) minimum clearance to combustibles. § R1001.11.
  • The airspace shall not be filled, except with noncombustible material or to provide fireblocking installed per the fireblocking rules. § R1001.11.

Hearth / hearth‑extension distances that affect surrounding combustibles

  • Hearth extension minimums are part of the same chapter and are frequently decision‑relevant when locating trim or flooring adjacent to the hearth. See § R1001.10 and Table R1001.1 for quick reference.

Decision‑relevant dimensions (quick table)

Item Value Code Reference
Front & side clearance (masonry fireplace faces to combustibles) 2 in (51 mm) § R1001.11
Back clearance (masonry fireplace back face to combustibles) 4 in (102 mm) § R1001.11
Combustible trim allowed to abut sidewalls/hearth extension Provided the trim is not less than 8 in (203 mm) from the inside surface of the nearest firebox lining (see Figure R1001.1) § R1001.11, Exception 3 & Figure R1001.1 (Table R1001.1)
Combustible mantel minimum distance to opening Not within 6 in (153 mm) of the fireplace opening § R1001.11, Exception 4
Mantel projection limit (above opening and within 12 in) Maximum projection = 1/8 in per 1 in of vertical distance from opening (i.e., 1/8" × distance in inches) § R1001.11, Exception 4
Mantel side projection threshold If a side mantel projection is > 1½ in (38 mm) from the face, additional clearance equal to the projection is required § R1001.11, Exception 4
Hearth extension (front) 16 in in front for openings < 6 ft²; 20 in for openings ≥ 6 ft² § R1001.10 & Table R1001.1

Notes:

  • The Figure R1001.1 and the Table R1001.1 summary show typical construction and where letters in the table refer to specific distances; consult those illustrations when deciding whether trim may abut the masonry.

Mantels and combustible trim — how the projection rule works

  • A combustible mantel placed directly on the masonry face is allowed provided it is not within 6 inches of the opening and its projection is limited as described above. The projection limit is proportional: for each inch of vertical distance above the opening (up to 12 inches), the mantel may project 1/8 inch. This is an explicit exception in § R1001.11, Exception 4.
  • If a side trim projects more than 1½ inches, add that projection to the required clearance (effectively increasing the required standoff). § R1001.11, Exception 4.

Exceptions & special cases

  • Listed masonry fireplaces that are specifically listed and labeled for contact with combustibles (per UL 127) may have combustibles in contact with their exterior surfaces when installed per the manufacturer’s instructions. § R1001.11, Exception 1.
  • Where a masonry fireplace is part of a masonry or concrete wall, combustible materials are not permitted in contact with that wall if they are less than 12 inches (306 mm) from the inside surface of the nearest firebox lining. § R1001.11, Exception 2.
  • The “abut” allowance for exposed combustible trim (i.e., trim edges or sheathing that touch the masonry sidewall or hearth extension) is limited by the minimum 8‑inch distance to the inside surface of the firebox lining in the Residential Code illustration — review Figure R1001.1 for the configuration that allows abutting. § R1001.11, Exception 3; Figure R1001.1.
  • Manufacturer instructions and listings override the generic clearance rule where an assembly is specifically listed for contact — always follow the listing/instructions when present. § R1001.11, Exception 1.

Common mistakes

  • Assuming “abut allowed” means anything goes: the abut exception requires the trim to be a specified distance from the inside of the firebox lining (not just from the masonry face). See § R1001.11, Exception 3.
  • Filling the required airspace with insulation or combustible filler. The code requires that the airspace remain, except for noncombustible material or approved fireblocking. § R1001.11.
  • Placing a mantel too close or making it project more than the 1/8 in per 1 in rule within the 12‑inch zone above the opening — the proportional projection rule is easily miscalculated. § R1001.11, Exception 4.
  • Mixing chimney clearance rules with fireplace rules. Chimney clearances (outside vs inside wall) are handled elsewhere (see related provisions) and have different numeric values. § R1003.19 (chimney clearances) — consult the chimney section for those specifics.

Worked example

Scenario: A homeowner has a masonry fireplace with an opening whose top is 9 inches below the planned bottom of a wooden mantel shelf. The mantel shelf would project 1.5 inches from the face of the fireplace.

Step 1 — Is the mantel at least the minimum vertical distance from the opening?

  • Mantels must not be placed within 6 inches of the fireplace opening. 9 inches is greater than 6 inches, so that pass. § R1001.11, Exception 4.

Step 2 — Does the projection comply with the proportional rule?

  • The projection allowed = (vertical distance in inches) × (1/8 in per 1 in). For 9 in vertical distance: 9 × 1/8 = 1.125 inches allowed. The proposed projection is 1.5 inches, which exceeds 1.125 in and therefore does not comply. § R1001.11, Exception 4.

Step 3 — Remedy options:

  • Reduce mantel projection to ≤ 1.125 in, or raise the mantel so the vertical distance is greater (e.g., at 12 in the allowed projection = 12 × 1/8 = 1.5 in), or use a noncombustible mantel or listed assembly that allows the intended projection. § R1001.11, Exception 4.

Related provisions (quick list)

  • § R1001.9 — Hearth and hearth extension construction requirements (thickness, noncombustible support).
  • § R1001.10 — Hearth extension dimensions (16 in / 20 in front and 8 in / 12 in sides depending on opening).
  • § R1001.11 — Fireplace clearance (front/side/back clearances and exceptions; controlling section for this page).
  • § R1001.12 — Fireplace fireblocking (how and where to fireblock spaces around fireplaces).
  • Table R1001.1 / Figure R1001.1 — Summary table and figure showing typical dimensions and the referenced letters used in the table. Useful for visual decisions about abutting trim.
  • § R1003.19 (and related chimney provisions) — Chimney clearance rules (different numeric clearances and exceptions).

Code references

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

  • CRC § 21-12 High relevance — show source text
    1. Where masonry fireplaces are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.

    21-12 2025 CALIFORNIA BUILDING CODE

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

    MASONRY

    1. Exposed combustible trim and the edges of sheathing materials, such as wood siding, flooring and drywall, are permitted to abut the masonry fireplace sidewalls and hearth extension, in accordance with Figure 2111.12, provided that such combustible trim or sheathing is not less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.
    2. Exposed combustible mantels or trim is permitted to be placed directly on the masonry fireplace front surrounding the fireplace opening, provided that such combustible materials shall not be placed within 6 inches (153 mm) of a fireplace opening. Combustible material directly above and within 12 inches (305 mm) of the fireplace opening shall not project more than [1] / 8 inch (3.2 mm) for each 1-inch (25 mm) distance from such opening. Combustible materials located along the sides of the fireplace opening that project more than 1 [1] / 2 inches (38 mm) from the face of the fireplace shall have an additional clearance equal to the projection.

    FIGURE 2111.12—ILLUSTRATION OF EXCEPTION TO FIREPLACE CLEARANCE PROVISION

    EDGE ABUTTING MASONRY

    2 ″ CLEARANCE (AIRSPACE) TO COMBUSTIBLE FRAMING

    For SI: 1 inch = 25.4 mm

    2111.13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.

    2111.14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.

    2111.14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.

    MASONRY
    COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB
    FRAME W
    WOOD MANT
    spaces between fireplaces and floors and
    al securely fastened in place. The fireblock
    nd shall only be placed on strips of metal
    r masonry fireplaces covered in this sect
    s the room is mechanically ventilated an
    es. Exterior combustion air ducts for fact
    o the fireplace manufacturer’s instruction    		 COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB    		 Col3
    spaces between fireplaces and floors and
    al securely fastened in place.
  • CRC § 8.1 High relevance — show source text

    R1001.8.1 Smoke chamber dimensions. The inside height of the smoke chamber from the fireplace throat to the beginning of the flue shall not be greater than the inside width of the fireplace opening. The inside surface of the smoke chamber shall not be inclined more than 45 degrees (0.79 rad) from vertical where prefabricated smoke chamber linings are used or where the smoke chamber walls are rolled or sloped rather than corbeled. Where the inside surface of the smoke chamber is formed by corbeled masonry, the walls shall not be corbeled more than 30 degrees (0.52 rad) from vertical.

    R1001.9 Hearth and hearth extension. Masonry fireplace hearths and hearth extensions shall be constructed of concrete or masonry, supported by noncombustible materials, and reinforced to carry their own weight and all imposed loads. Combustible material shall not remain against the underside of hearths and hearth extensions after construction.

    R1001.9.1 Hearth thickness. The minimum thickness of fireplace hearths shall be 4 inches (102 mm).

    R1001.9.2 Hearth extension thickness. The minimum thickness of hearth extensions shall be 2 inches (51 mm).

    Exception: Where the bottom of the firebox opening is raised not less than 8 inches (203 mm) above the top of the hearth extension, a hearth extension of not less than [3] / 8 -inch-thick (10 mm) brick, concrete, stone, tile or other approved noncombustible material is permitted.

    2025 CALIFORNIA RESIDENTIAL CODE 10-5

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

    CHIMNEYS AND FIREPLACES

    R1001.10 Hearth extension dimensions. Hearth extensions shall extend not less than 16 inches (406 mm) in front of and not less than 8 inches (203 mm) beyond each side of the fireplace opening. Where the fireplace opening is 6 square feet (0.6 m [2] ) or larger, the hearth extension shall extend not less than 20 inches (508 mm) in front of and not less than 12 inches (305 mm) beyond each side of the fireplace opening.

    R1001.11 Fireplace clearance. Wood beams, joists, studs and other combustible material shall have a clearance of not less than 2 inches (51 mm) from the front faces and sides of masonry fireplaces and not less than 4 inches (102 mm) from the back faces of masonry fireplaces. The airspace shall not be filled, except for noncombustible material or to provide fireblocking in accordance with Section R1001.12.

    Exceptions:

    1. Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL 127 and installed in accordance with the manufacturer’s instructions are permitted to have combustible material in contact with their exterior surfaces.

    2. Where masonry fireplaces are part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.

    3. Exposed combustible trim and the edges of sheathing materials such as wood siding, flooring and gypsum board shall be permitted to abut the masonry fireplace sidewalls and hearth extension in accordance with Figure R1001.11, provided that such combustible trim or sheathing is not less than 8 inches (203 mm) from the inside surface of the nearest firebox

  • CRC § 0.6 High relevance — show source text

    R1001.10 Hearth extension dimensions. Hearth extensions shall extend not less than 16 inches (406 mm) in front of and not less than 8 inches (203 mm) beyond each side of the fireplace opening. Where the fireplace opening is 6 square feet (0.6 m [2] ) or larger, the hearth extension shall extend not less than 20 inches (508 mm) in front of and not less than 12 inches (305 mm) beyond each side of the fireplace opening.

    R1001.11 Fireplace clearance. Wood beams, joists, studs and other combustible material shall have a clearance of not less than 2 inches (51 mm) from the front faces and sides of masonry fireplaces and not less than 4 inches (102 mm) from the back faces of masonry fireplaces. The airspace shall not be filled, except for noncombustible material or to provide fireblocking in accordance with Section R1001.12.

    Exceptions:

    1. Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL 127 and installed in accordance with the manufacturer’s instructions are permitted to have combustible material in contact with their exterior surfaces.

    2. Where masonry fireplaces are part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.

    3. Exposed combustible trim and the edges of sheathing materials such as wood siding, flooring and gypsum board shall be permitted to abut the masonry fireplace sidewalls and hearth extension in accordance with Figure R1001.11, provided that such combustible trim or sheathing is not less than 8 inches (203 mm) from the inside surface of the nearest firebox

    For SI: 1 inch = 25.4 mm.

    masonry, that is designed to absorb and store heat from a solid-fuel fire built in the firebox by routing the exhaust gases through

    |e fireplace opening is 6 square feet (0.6 m2) or larger, such combustible tri
    masonry fireplace sidewalls and hearth extension provided that such co
    inches (305 mm) from the inside surface of the nearest firebox lining.
    ustible mantels or trim is permitted to be placed directly on the masonry f
    ng providing such combustible materials are not placed within 6 inches (1
    aterial within 12 inches (306 mm) of the fireplace opening shall not projec
    mm) distance from such an opening.
    FIGURE R1001.11—CLEARANCE FROM COMBUSTIBLES
    MASONRY
    COMBUSTIBLE SHEATHING
    EDGE ABUTTING MASONRY
    12 IN. FROM FIREBOX
    FRAME WALL
    2 IN. CLEARANCE (AIRSPA
    TO COMBUSTIBLE FRAMIN
    WOOD MANTEL
    cking. Fireplace fireblocking shall comply with the provisions of Section R
    ories. Listed and labeled fireplace accessories shall be installed in accorda
    r’s instructions.

  • CRC § 3.2 High relevance — show source text

    Exceptions:

    1. Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL 127 and installed in accordance with the manufacturer’s instructions are permitted to have combustible material in contact with their exterior surfaces.

    2. Where masonry fireplaces are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.

    3. Exposed combustible trim and the edges of sheathing materials, such as wood siding, flooring and drywall, are permitted to abut the masonry fireplace sidewalls and hearth extension, in accordance with Figure 2111 A .12, provided that such combustible trim or sheathing is not less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.

    4. Exposed combustible mantels or trim is permitted to be placed directly on the masonry fireplace front surrounding the fireplace opening, provided that such combustible materials shall not be placed within 6 inches (153 mm) of a fireplace opening. Combustible material directly above and within 12 inches (305 mm) of the fireplace opening shall not project more than [1] / 8 inch (3.2 mm) for each 1-inch (25 mm) distance from such opening. Combustible materials located along the sides of the fireplace opening that project more than 1 [1] / 2 inches (38 mm) from the face of the fireplace shall have an additional clearance equal to the projection.

    FIGURE 2111 A .12—ILLUSTRATION OF EXCEPTION TO FIREPLACE CLEARANCE PROVISION

    EDGE ABUTTING MASONRY

    2 ″ CLEARANCE (AIRSPACE) TO COMBUSTIBLE FRAMING

    WOOD MANTEL

    MASONRY
    COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB
    FRAME W    		 COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB    		 Col3
    COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    MASONRY
    2″ CLEAR
    TO COMB
    FRAME W

    For SI: 1 inch = 25.4 mm

    2111 A .13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.

    2111 A .14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.

    2111 A .14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.

    21A-12 2025 CALIFORNIA BUILDING CODE

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

    MASONRY

  • CRC § 2111.10.1 High relevance — show source text

    2111.10.1 Hearth thickness. The minimum thickness of fireplace hearths shall be 4 inches (102 mm).

    2111.10.2 Hearth extension thickness. The minimum thickness of hearth extensions shall be 2 inches (51 mm).

    Exception: Where the bottom of the firebox opening is raised not less than 8 inches (203 mm) above the top of the hearth extension, a hearth extension of not less than [3] / 8 -inch-thick (9.5 mm) brick, concrete, stone, tile or other approved noncombustible material is permitted.

    2111.11 Hearth extension dimensions. Hearth extensions shall extend not less than 16 inches (406 mm) in front of, and not less than 8 inches (203 mm) beyond, each side of the fireplace opening. Where the fireplace opening is 6 square feet (0.557 m [2] ) or larger, the hearth extension shall extend not less than 20 inches (508 mm) in front of, and not less than 12 inches (305 mm) beyond, each side of the fireplace opening.

    2111.12 Fireplace clearance. Any portion of a masonry fireplace located in the interior of a building or within the exterior wall of a building shall have a clearance to combustibles of not less than 2 inches (51 mm) from the front faces and sides of masonry fireplaces and not less than 4 inches (102 mm) from the back faces of masonry fireplaces. The airspace shall not be filled, except to provide fireblocking in accordance with Section 2111.13.

    Exceptions:

    1. Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL 127 and installed in accordance with the manufacturer’s instructions are permitted to have combustible material in contact with their exterior surfaces.

    2. Where masonry fireplaces are constructed as part of masonry or concrete walls, combustible materials shall not be in contact with the masonry or concrete walls less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.

    21-12 2025 CALIFORNIA BUILDING CODE

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

    MASONRY

    1. Exposed combustible trim and the edges of sheathing materials, such as wood siding, flooring and drywall, are permitted to abut the masonry fireplace sidewalls and hearth extension, in accordance with Figure 2111.12, provided that such combustible trim or sheathing is not less than 12 inches (306 mm) from the inside surface of the nearest firebox lining.
    2. Exposed combustible mantels or trim is permitted to be placed directly on the masonry fireplace front surrounding the fireplace opening, provided that such combustible materials shall not be placed within 6 inches (153 mm) of a fireplace opening. Combustible material directly above and within 12 inches (305 mm) of the fireplace opening shall not project more than [1] / 8 inch (3.2 mm) for each 1-inch (25 mm) distance from such opening. Combustible materials located along the sides of the fireplace opening that project more than 1 [1] / 2 inches (38 mm) from the face of the fireplace shall have an additional clearance equal to the projection.

    FIGURE 2111.12—ILLUSTRATION OF EXCEPTION TO FIREPLACE CLEARANCE PROVISION

    EDGE ABUTTING MASONRY

    2 ″ CLEARANCE (AIRSPACE) TO COMBUSTIBLE FRAMING

  • CRC § 25.4 High relevance — show source text

    For SI: 1 inch = 25.4 mm.

    masonry, that is designed to absorb and store heat from a solid-fuel fire built in the firebox by routing the exhaust gases through

    e fireplace opening is 6 square feet (0.6 m2) or larger, such combustible tri
    masonry fireplace sidewalls and hearth extension provided that such co
    inches (305 mm) from the inside surface of the nearest firebox lining.
    ustible mantels or trim is permitted to be placed directly on the masonry f
    ng providing such combustible materials are not placed within 6 inches (1
    aterial within 12 inches (306 mm) of the fireplace opening shall not projec
    mm) distance from such an opening.
    FIGURE R1001.11—CLEARANCE FROM COMBUSTIBLES
    MASONRY
    COMBUSTIBLE SHEATHING
    EDGE ABUTTING MASONRY
    12 IN. FROM FIREBOX
    FRAME WALL
    2 IN. CLEARANCE (AIRSPA
    TO COMBUSTIBLE FRAMIN
    WOOD MANTEL
    cking. Fireplace fireblocking shall comply with the provisions of Section R
    ories. Listed and labeled fireplace accessories shall be installed in accorda
    r’s instructions. Fireplace accessories shall comply with UL 907.
    SECTION R1002—MASONRY HEATERS
    onry heater is a heating appliance constructed of concrete or solid maso    		 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 Col11 Col12 Col13 Col14 Col15 Col16 Col17 Col18 Col19 Col20 Col21 Col22 Col23 Col24 Col25 Col26
    cking. Firepl
    ories. Listed
    r’s instructio
    onry heater

    WOO
    cking. Firepl
    ories. Listed
    r’s instructio
    onry heater

    WOO
    cking. Firepl
    **ories.
  • CRC § 25.4 High relevance — show source text

    WOOD MANTEL

    MASONRY
    COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB
    FRAME W    		 COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB    		 Col3
    COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    MASONRY
    2″ CLEAR
    TO COMB
    FRAME W

    For SI: 1 inch = 25.4 mm

    2111 A .13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.

    2111 A .14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.

    2111 A .14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.

    21A-12 2025 CALIFORNIA BUILDING CODE

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

    MASONRY

    2111 A .14.2 Masonry fireplaces. Listed combustion air ducts for masonry fireplaces shall be installed according to the terms of their listing and manufacturer’s instructions.

    2111 A .14.3 Exterior air intake. The exterior air intake shall be capable of providing all combustion air from the exterior of the dwelling. The exterior air intake shall not be located within a garage, attic, basement or crawl space of the dwelling nor shall the air intake be located at an elevation higher than the firebox. The exterior air intake shall be covered with a corrosion-resistant screen of [1] / 4 -inch (6.4 mm) mesh.

    2111 A .14.4 Clearance. Unlisted combustion air ducts shall be installed with a minimum 1-inch (25 mm) clearance to combustibles for all parts of the duct within 5 feet (1524 mm) of the duct outlet. 2111 A .14.5 Passageway. The combustion air passageway shall be not less than 6 square inches (3870 mm [2] ) and not more than 55 square inches (0.035 m [2] ), except that combustion air systems for listed fireplaces or for fireplaces tested for emissions shall be constructed according to the fireplace manufacturer’s instructions.

    2111 A .14.6 Outlet. The exterior air outlet is permitted to be located in the back or sides of the firebox chamber or within 24 inches (610 mm) of the firebox opening on or near the floor. The outlet shall be closable and designed to prevent burning material from dropping into concealed combustible spaces.

    SECTION 2112 A —MASONRY HEATERS

  • 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).

    2025 CALIFORNIA BUILDING CODE 21A-17

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

    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 § 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.

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    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 § 25.4 High relevance — show source text

    2 ″ CLEARANCE (AIRSPACE) TO COMBUSTIBLE FRAMING

    For SI: 1 inch = 25.4 mm

    2111.13 Fireplace fireblocking. All spaces between fireplaces and floors and ceilings through which fireplaces pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between wood joists, beams or headers shall be to a depth of 1 inch (25 mm) and shall only be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.

    2111.14 Exterior air. Factory-built or masonry fireplaces covered in this section shall be equipped with an exterior air supply to ensure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive.

    2111.14.1 Factory-built fireplaces. Exterior combustion air ducts for factory-built fireplaces shall be listed components of the fireplace, and installed according to the fireplace manufacturer’s instructions.

    MASONRY
    COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB
    FRAME W
    WOOD MANT
    spaces between fireplaces and floors and
    al securely fastened in place. The fireblock
    nd shall only be placed on strips of metal
    r masonry fireplaces covered in this sect
    s the room is mechanically ventilated an
    es. Exterior combustion air ducts for fact
    o the fireplace manufacturer’s instruction    		 COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    2″ CLEAR
    TO COMB    		 Col3
    spaces between fireplaces and floors and
    al securely fastened in place. The fireblock
    nd shall only be placed on strips of metal
    r masonry fireplaces covered in this sect
    s the room is mechanically ventilated an
    es. Exterior combustion air ducts for fact
    o the fireplace manufacturer’s instruction
    COMBUSTIBL
    EDGE ABUTTI
    12″ MIN FROM
    MASONRY
    2″ CLEAR
    TO COMB
    FRAME W
    WOOD MANT

    2111.14.2 Masonry fireplaces. Listed combustion air ducts for masonry fireplaces shall be installed according to the terms of their listing and manufacturer’s instructions.

    2111.14.3 Exterior air intake. The exterior air intake shall be capable of providing all combustion air from the exterior of the dwelling. The exterior air intake shall not be located within a garage, attic, basement or crawl space of the dwelling nor shall the air intake be located at an elevation higher than the firebox. The exterior air intake shall be covered with a corrosion-resistant screen of [1] / 4 -inch (6.4 mm) mesh.

    2111.14.4 Clearance. Unlisted combustion air ducts shall be installed with a minimum 1-inch (25 mm) clearance to combustibles for all parts of the duct within 5 feet (1524 mm) of the duct outlet. 2111.14.5 Passageway. The combustion air passageway shall be not less than 6 square inches (3870 mm [2] ) and not more than 55 square inches (0.035 m [2] ), except that combustion air systems for listed fireplaces or for fireplaces tested for emissions shall be constructed according to the fireplace manufacturer’s instructions.

  • 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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    MASONRY

    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 § 25.4 High relevance — show source text

    | |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. Not required in Seismic Design Category A or B.|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. Not required in Seismic Design Category A or B.|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. Not required in Seismic Design Category A or B.|

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    For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

Frequently asked questions

Can I attach wood trim directly to the side of a masonry fireplace?

Yes — the code allows exposed combustible trim to abut the masonry fireplace sidewalls or the hearth extension under the configuration shown in Figure R1001.1, provided that trimming is not less than 8 inches from the inside surface of the nearest firebox lining (see § R1001.11, Exception 3).

How far can a wooden mantel project from the face and remain code‑compliant?

For mantels within 12 inches above the opening, the projection is limited to 1/8 inch for each 1 inch of vertical distance from the opening. If a side mantel projects more than 1½ inches, an additional clearance equal to that projection is required. § R1001.11, Exception 4.

Is it okay to fill the airspace behind the fireplace with insulation?

No. The required airspace (2 inches front/sides, 4 inches back) shall not be filled, except with noncombustible material or to provide approved fireblocking in accordance with the fireblocking rules. § R1001.11.

Does a manufacturer listing change these clearances?

Yes. A masonry fireplace listed and labeled for contact with combustibles (e.g., per UL 127) and installed per manufacturer instructions may be in contact with combustible materials despite the general airspace rule. § R1001.11, Exception 1.

If my fireplace is built into a concrete wall, can I put wood paneling on that wall?

Only if the wood paneling is not in contact with the masonry/concrete within 12 inches of the inside surface of the nearest firebox lining. See § R1001.11, Exception 2.

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Masonry Fireplaces

California Residential Code