About this chapter: Chapter 10 contains requirements for the construction, seismic reinforcing and anchorage of masonry chimneys and fireplaces; and establishes standards for the use and installation of factory-built chimneys, fireplaces and masonry heaters. Chimneys and fireplaces constructed of masonry rely on prescriptive requirements for the details of their construction; factory-built versions rely on the listing and labeling method of approval.
|Hearth slab thickness||A||4 inches|
|Hearth extension||B||8-inch fireplace opening < 6 square feet.|
|(each side of opening)||12-inch fireplace opening ≥ 6 square feet.|
|Hearth extension||C||16-inch fireplace opening < 6 square feet.|
|(front of opening)||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 firebrick 1/4-inch maximum.|
|Distance from top of opening to throat||F||8 inches|
|Smoke chamber wall thickness||G||6 inches|
|Unlined walls||8 inches|
|Chimney||H||Four No. 4 full-length bars for chimney up to 40 inches wide.|
|Vertical reinforcingb||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.|
|Combustible material||See Sections R1001.11 and R1003.18.|
|Mantel and trim||See Section R1001.11, Exception 4.|
|Above roof||3 feet at roofline and 2 feet at 10 feet.|
|Strap||3/16-inch × 1-inch|
|Embedment into chimney||12 inches hooked around outer bar with 6-inch extension.|
|Fasten to||4 joists|
|Bolts||Two 1/2-inch diameter.|
|Thickness||12 inches min.|
|Width||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 requirements of the code, see the indicated section of text.
The firebox of a concrete or masonry fireplace shall have a depth of not less than 20 inches (508 mm). The throat shall be not less than 8 inches (203 mm) above the fireplace opening. The throat opening shall be not less than 4 inches (102 mm) deep. The cross-sectional area of the passageway above the firebox, including the throat, damper and smoke chamber, shall be not less than the cross-sectional area of the flue.
The minimum thickness of hearth extensions shall be 2 inches (51 mm).
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 to provide fireblocking in accordance with Section R1001.12.
Masonry heaters shall be installed in accordance with this section and comply with one of the following:
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.
Where a spark arrestor is installed on a masonry chimney, the spark arrestor shall meet all of the following requirements:
Flue lining systems shall comply with one of the following:
Where a flue is relined with a material not complying with Section R1003.11.1, the chimney shall be plainly and permanently identified by a label attached to a wall, ceiling or other conspicuous location adjacent to where the connector enters the chimney. The label shall include the following message or equivalent language:
Clay flue liners shall be installed in accordance with ASTM C1283 and extend from a point not less than 8 inches (203 mm) below the lowest inlet or, in the case of fireplaces, from the top of the smoke chamber to a point above the enclosing walls. The lining shall be carried up vertically, with a slope not greater than 30 degrees (0.52 rad) from the vertical.
Clay flue liners shall be laid in medium-duty water insoluble refractory mortar conforming to ASTM C199 with tight mortar joints left smooth on the inside and installed to maintain an airspace or insulation not to exceed the thickness of the flue liner separating the flue liners from the interior face of the chimney masonry walls. Flue liners shall be supported on all sides. Only enough mortar shall be placed to make the joint and hold the liners in position.
Where two or more flues are located in the same chimney, masonry wythes shall be built between adjacent flue linings. The masonry wythes shall be not less than 4 inches (102 mm) thick and bonded into the walls of the chimney.
|FLUE SIZE, INSIDE DIAMETER (inches)||CROSS-SECTIONAL AREA
For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2.
|FLUE SIZE, OUTSIDE NOMINAL DIMENSIONS (inches)||CROSS-SECTIONAL AREA
|4.5 × 8.5||23|
|4.5 × 13||34|
|8 × 8||42|
|8.5 × 8.5||49|
|8 × 12||67|
|8.5 × 13||76|
|12 × 12||102|
|8.5 × 18||101|
|13 × 13||127|
|12 × 16||131|
|13 × 18||173|
|16 × 16||181|
|16 × 20||222|
|18 × 18||233|
|20 × 20||298|
|20 × 24||335|
|24 × 24||431|
For SI: 1 inch = 25.4 mm, 1 square inch = 645.16 mm2.
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.
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 fire blocking in accordance with Section R1003.19.
|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|
Factory-built chimneys installed in dwelling units with solid-fuel-burning appliances shall comply with the Type HT requirements of UL 103 and shall be marked "Type HT" and "Residential Type and Building Heating Appliance Chimney."
Chimneys for use with open combustion chamber appliances installed in buildings other than dwelling units shall comply with the requirements of UL 103 and shall be marked "Building Heating Appliance Chimney" or "Residential Type and Building Heating Appliance Chimney."