Chimney and Fireplace Clearance Codes
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International Code References
Code: R1001.15 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 minimumair space 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 air space clearance of 1 inch (25.4 mm). The air space shall not be filled, except to provide fire blocking in accordance with Section R1001.16.
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 manufacturers installation instructions are permitted to have combustible material in contact with their exterior surfaces.
2. When 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 (306 mm) from the inside surface of the nearest flue lining.
3. Exposed combustible trim and the edges of sheathing materials, such as wood siding and flooring, shall be permitted to abut the masonry chimney side walls, in accordance with Figure R1001.15 provided such combustible trim or sheathing is a minimum of 12 inches (306 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 (25.4 mm).
Commentary
Current code on clearance to combustible materials from masonry chimneys is basically one unbuildable paragraph with three exceptions.
Then there is an obvoius exception for any listed and labeled system
Exception 2 permits masonry chimneys which are part of masonry walls to be in contact with combustibles provided the combustible are at least 12" from an interior flue lining. This is a relatively new code provision and is interesting becasue it shows how far we have slid since houses were built of brick. Without this exception masonry chimenys could not be built within masonry walls if those walls were anywhere in contact with combustibles. This exception provides something of a solution in that for the first time in many years, it allows thickness and mass to compensate for clearance.
Exception 3 is a litany of other specific situations in which combustible trim, flooring and siding may touch the masonry. Again the 12" rule is mentioned and is precident-setting in establishing the principle of thickness and mass as a substitute for air space. We think 8" of solid masonry would be an adequate alternative to 4" of masonry plus 2" of air space based on the experience of historic fire prevention strategies and our limited testing
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 manufacturers installation instructions are permitted to have combustible material in contact with their exterior surfaces.
2. When 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 (306 mm) from the inside surface of the nearest flue lining.
3. Exposed combustible trim and the edges of sheathing materials, such as wood siding and flooring, shall be permitted to abut the masonry chimney side walls, in accordance with Figure R1001.15 provided such combustible trim or sheathing is a minimum of 12 inches (306 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 (25.4 mm).
Commentary
Current code on clearance to combustible materials from masonry chimneys is basically one unbuildable paragraph with three exceptions.
Then there is an obvoius exception for any listed and labeled system
Exception 2 permits masonry chimneys which are part of masonry walls to be in contact with combustibles provided the combustible are at least 12" from an interior flue lining. This is a relatively new code provision and is interesting becasue it shows how far we have slid since houses were built of brick. Without this exception masonry chimenys could not be built within masonry walls if those walls were anywhere in contact with combustibles. This exception provides something of a solution in that for the first time in many years, it allows thickness and mass to compensate for clearance.
Exception 3 is a litany of other specific situations in which combustible trim, flooring and siding may touch the masonry. Again the 12" rule is mentioned and is precident-setting in establishing the principle of thickness and mass as a substitute for air space. We think 8" of solid masonry would be an adequate alternative to 4" of masonry plus 2" of air space based on the experience of historic fire prevention strategies and our limited testing
Code: R1003. 11 Fireplace Clearances
All 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 air space shall not be filled, except to provide fire blocking in accordance with Section R1003.13.
Exceptions:
1. Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL127 and installed in accordance with the manufacturers installation instructions are permitted to have combustible material in contact with their exterior surfaces.
2. When 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 (305 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 shall be permitted to abut the masonry fireplace side walls and hearth extension in accordance with Figure R1003.12, provided such combustible trim or sheathing is a minimum of 12 inches (305 mm) from the inside surface of the nearest firebox lining.
4. Exposed combustible mantels or trim may be placed directly on the masonry fireplace front surrounding the fireplace opening providing such combustible materials shall not be placed within 6 inches (152 mm) of a fireplace opening. Combustible material within 12 inches (306 mm) of the fireplace opening shall not project more than 1/8 inch (3.2 mm) for each 1-inch (25.4 mm) distance from such an opening.
Commentary
Current code on clearance to combustible materials from masonry fireplaces is basically one unbuildable paragraph with four exceptions (Did I say tis before?). It is noteworthy that the clearance at the back of the firebox was increased from 2" to 4" based on evidence that the "hot spot" is right behind the fireplace.
Once again, if the fireplce is proprietary and listed, some manufacturer has taken responsibility for it and code allows any exception sanctioned by the manufacturer of a listed system.
Exception 2, as in the chimney section, permits masonry fireplaces which are part of masonry walls to be in contact with combustibles provided the combustible are at least 12" from an interior flue lining. Again, this language allows thickness and mass to compensate for clearance.
Exception 3 allows combustible trim, flooring and siding to touch the masonry repeating the 12" distance from an interior lining surface rule and reinforcing the principle of thickness and mass as a substitute for air space. We agree with this exception based on history and our testing.
Exception 4 allows mantels and trim on the front of a fireplace to be even closer to the firebox (6") as it has been shown over many hundreds of years not to be a problem.
In summary, the code could be more sucinctly and directly written instead of being a list of exceptions to an umbuildable general rule. The idea that mass and thickness may compensate for clearance is important, however. Another principle is also improtant but is not stated. It's the idea that combustibles that ar exposed such as trim, siding, mantles and flooring, are not as dangerous or insidius as combustibles like the framing you can't see. The idea that the chimney could be bare (at least not totally enclosed with framing) and that trim could touch it here and there would be safer is implied if not stated. It's also the way houses used to be built.
Exceptions:
1. Masonry fireplaces listed and labeled for use in contact with combustibles in accordance with UL127 and installed in accordance with the manufacturers installation instructions are permitted to have combustible material in contact with their exterior surfaces.
2. When 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 (305 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 shall be permitted to abut the masonry fireplace side walls and hearth extension in accordance with Figure R1003.12, provided such combustible trim or sheathing is a minimum of 12 inches (305 mm) from the inside surface of the nearest firebox lining.
4. Exposed combustible mantels or trim may be placed directly on the masonry fireplace front surrounding the fireplace opening providing such combustible materials shall not be placed within 6 inches (152 mm) of a fireplace opening. Combustible material within 12 inches (306 mm) of the fireplace opening shall not project more than 1/8 inch (3.2 mm) for each 1-inch (25.4 mm) distance from such an opening.
Commentary
Current code on clearance to combustible materials from masonry fireplaces is basically one unbuildable paragraph with four exceptions (Did I say tis before?). It is noteworthy that the clearance at the back of the firebox was increased from 2" to 4" based on evidence that the "hot spot" is right behind the fireplace.
Once again, if the fireplce is proprietary and listed, some manufacturer has taken responsibility for it and code allows any exception sanctioned by the manufacturer of a listed system.
Exception 2, as in the chimney section, permits masonry fireplaces which are part of masonry walls to be in contact with combustibles provided the combustible are at least 12" from an interior flue lining. Again, this language allows thickness and mass to compensate for clearance.
Exception 3 allows combustible trim, flooring and siding to touch the masonry repeating the 12" distance from an interior lining surface rule and reinforcing the principle of thickness and mass as a substitute for air space. We agree with this exception based on history and our testing.
Exception 4 allows mantels and trim on the front of a fireplace to be even closer to the firebox (6") as it has been shown over many hundreds of years not to be a problem.
In summary, the code could be more sucinctly and directly written instead of being a list of exceptions to an umbuildable general rule. The idea that mass and thickness may compensate for clearance is important, however. Another principle is also improtant but is not stated. It's the idea that combustibles that ar exposed such as trim, siding, mantles and flooring, are not as dangerous or insidius as combustibles like the framing you can't see. The idea that the chimney could be bare (at least not totally enclosed with framing) and that trim could touch it here and there would be safer is implied if not stated. It's also the way houses used to be built.
Code: R1003.5 Firebox walls
Masonry fireboxes shall be constructed of solid masonry units, hollow masonry units grouted solid, stone or concrete. When a lining of firebrick at least 2 inches (51 mm) in thickness or other approved lining is provided, the minimum thickness of back and side walls shall each be 8 inches (203 mm) of solid masonry, including the lin- ing. The width of joints between firebricks shall not be greater than 1/4 inch (6.4 mm). When no lining is provided, the total minimum thickness of back and side walls shall be 10 inches (254 mm) of solid masonry. Firebrick shall conform to ASTM C 27 or C 1261 and shall be laid with medium-duty refractory mortar conforming to ASTM C 199.
Code: R1003.9 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. No combustible material shall remain against the underside of hearths and hearth extensions after construction.
Code: R1003.9.1 Hearth thickness
The minimum thickness of fireplace hearths shall be 4 inches (102 mm).
Code: R1003.9.2 Hearth extension thickness
The minimum thickness of hearth extensions shall be 2 inches (51 mm).
Exception: When the bottom of the firebox opening is raised at least 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.
Exception: When the bottom of the firebox opening is raised at least 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.
Code: R1003.8 Smoke chamber
Smoke chamber walls shall be constructed of solid masonry units, hollow masonry units grouted solid, stone or concrete. Corbelling of masonry units shall not leave unit cores exposed to the inside of the smoke chamber. When a lining of firebrick at least 2 inches (51 mm) thick, or a lining of vitrified clay at least 5 /8 inch (15.9 mm) thick, is provided, the total minimum thickness of front, back and side walls shall be 6 inches (152 mm) of solid masonry, in- cluding the lining. Firebrick shall conform to ASTMC 27 or C 1261 and shall be laid with medium-duty refractory mortar conforming to ASTM C 199. Where no lining is provided, the total minimumthickness of front, back and side walls shall be 8 inches (203 mm) of solid masonry. When the inside surface of the smoke chamber is formed by corbeled masonry, the inside surface shall be parged smooth.
R1003.8.1 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 smokechamber shall not be inclined more than 45 degrees (0.39 rad) from vertical when prefabricated smoke chamber linings are used or when the smoke chamber walls are rolled or sloped rather than corbeled. When the inside surface of the smoke chamber is formed by corbeled masonry, the walls shall not be corbeled more than 30 degrees (0.26 rad) from vertical.
R1003.8.1 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 smokechamber shall not be inclined more than 45 degrees (0.39 rad) from vertical when prefabricated smoke chamber linings are used or when the smoke chamber walls are rolled or sloped rather than corbeled. When the inside surface of the smoke chamber is formed by corbeled masonry, the walls shall not be corbeled more than 30 degrees (0.26 rad) from vertical.
Code: R1001.9 Flue lining (installation)
Flue liners shall be installed in accordance with ASTM C 1283 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 maximum slope no greater than 30 degrees from the vertical.
Fireclay flue liners shall be laid in medium-duty refractory mortar conforming to ASTMC199 with tight mortar joints left smooth on the inside and installed to maintain an air space or insulation not to exceed the thickness of the flue liner separating the flue liners from the interior face of the chimneymasonry walls. Flue lining shall be supported on all sides. Only enough mortar shall be placed to make the joint and hold the liners in position.
Fireclay flue liners shall be laid in medium-duty refractory mortar conforming to ASTMC199 with tight mortar joints left smooth on the inside and installed to maintain an air space or insulation not to exceed the thickness of the flue liner separating the flue liners from the interior face of the chimneymasonry walls. Flue lining shall be supported on all sides. Only enough mortar shall be placed to make the joint and hold the liners in position.
Code: R1003.3 Seismic reinforcing
Masonry or concrete chimneys in Seismic Design Categories D1 and D2 shall be reinforced. Reinforcing shall conform to the requirements set forth in Table R1003.1 and Section R609, Grouted Masonry.
Code: R1003.3.1 Vertical reinforcing
For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars shall be placed between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section R609. 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 flue incorporated in the chim- ney or for each additional 40 inches (1016 mm) in width or fraction there of.
Code: R1003.3.2 Horizontal reinforcing
Vertical reinforcement shall be placed within 1 /4 -inch (6.4 mm) ties, or other reinforcing of equivalent net cross-sectional area, placed in the bed joints according to Section R607 at a minimum of every 18 inches (457 mm) of vertical height. Two such ties shall be provided at each bend in the vertical bars.