Chimneys Connected to Roof Structure

    Scope Images
    Image
    This chimney was not adequately attached to the structure and fell away during an earthquake
    Scope

    Design or retrofit the chimney for adequate support and water protection.

    • Provide adequate connection of the chimney to roof framing to make the chimney more resistant to toppling in strong winds and seismic activity.
    • Install flashing that is properly integrated with the roof flashing to keep water out of the chimney and roof assemblies.

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

    Description

    One of the largest penetrations in a residential roof assembly is a chimney. Chimneys typically have numerous requirements beyond that of venting products of combustion. They must be adequately connected to the roof structure to resist wind and seismic loads based on site design wind speed and exposure category. Chimneys must also be waterproofed to resist rainwater entry during high wind events such as hurricanes.

    This guide provides guidance on securing and waterproofing of chimneys to resist toppling rainwater entry during high wind events such as hurricanes. In addition, this guide also covers construction guidelines for chimneys built on homes in earthquake zones. The guidance is applicable to both new construction and the re-roofing of existing roof assemblies.

    It is common for chimneys to significantly extend or protrude above roof surfaces in order to provide sufficient “draft” for the venting of products of combustion. This tends to expose the chimney surfaces to higher wind pressure differences than those acting on the field of the roof assembly. Chimneys, especially tall, narrow chimneys or those made of brick or stone that protrude high above the roof, are at an increased risk of damage and are prone to collapse under seismic forces. Not only will the collapse of a chimney damage the structural integrity of the roof and home, but they pose a significant risk of injury for occupants (FEMA P-530, 2020). These forces can be further increased when the chimney is located near the roof eave or rake edge. For these reasons, the chimney must be properly anchored. Waterproofing of the joint between the roof assembly and the chimney is significant in controlling rainwater entry during high wind events such as hurricanes.

    In its Fortified Home program, the Insurance Institute for Building and Home Safety (IBHS) requires that the chimney be adequately connected to the roof framing to prevent the chimney from collapsing or breaking away during high winds. See the CAD tab of this guide for a detail from IBHS that specifies a retrofit method for providing adequate anchorage of an existing chimney to the roof members. IBHS requires that if the chimney is more than 5 feet above the roof, support detailing must be specified by an engineer or licensed design professional. See the IBHS Fortified Home Hurricane Standards (2019) for additional details. More guidance is provided on the Retrofit tab. 

    Waterproofing of the connection between the roof assembly and the chimney is also important for controlling rainwater entry during high wind events such as hurricanes. The fundamental principle of waterproofing the connection between the roof assembly and the chimney is to connect the water control layer of the roof assembly to the water control layer of the chimney.

    In high wind zones, a fully adhered roof membrane underlayment should be installed over the roof deck sheathing. This underlayment water control layer needs to be connected to the water control layer of the chimney.

    The water control layer of a chimney is most commonly the brick layer or other exterior cladding comprising the structural enclosure supporting the chimney flue. The following description pertains to brick chimneys. If the chimney is enclosed with lumber framing and siding see the guides Step and Kick-Out Flashing at Roof-Wall Intersections and Flashing of Roof-Wall Intersections in Existing Homes for additional guidance on flashing and water sealing.

    The rainwater management of the brick layer is based on the rainwater shedding of individual bricks and the mortar connecting them to each other. This brick layer comprised of individual bricks and mortar needs to be connected to the fully adhered roof membrane underlayment.

    Metal flashing typically serves as a water control layer transition between the brick layer and the fully adhered roof membrane underlayment. The metal flashing consists of three elements – a base flashing, a step flashing, and a counterflashing.

    The base flashing should be sealed with a full bed of mastic to the top surface of the fully adhered roof membrane underlayment. A step flashing is then integrated in a layered manner with the asphalt shingle roofing. Counterflashing is embedded into the mortar joints of the brick layer and overlaps the base flashing and the step flashing, completing the waterproofing transition connecting the brick layer to the fully adhered roof membrane underlayment (Figure 1 and Figure 2).

    Right - Step flashing along a chimney is integrated in a layered manner with asphalt shingle roofing and topped with counterflashing that is embedded into brick mortar joint above.
    Figure 1. Step flashing along a chimney is integrated in a layered manner with asphalt shingle roofing and topped with counterflashing that is embedded into the brick mortar joint above. (Source: Building Science Corporation.)

     

    Right - Counterflashing tops a layer of step flashing which comes down above the asphalt shingle and a layer of L-shaped base flashing which comes down and extends below the shingle; the base flashing is adhered to the roof underlayment with mastic, shown in blue.
    Figure 2. Counterflashing tops a layer of step flashing which comes down above the asphalt shingle and a layer of L-shaped base flashing which comes down and extends below the shingle; the base flashing is adhered to the roof underlayment with mastic, shown in blue. (Source: Building Science Corporation.)

     

    If a fully adhered roof membrane is not installed over the entire surface area of the roof deck, alternative roof deck water control requirements are necessary to provide acceptable performance and acceptable risk in high wind zones. Alternative roof deck air sealing and water control requirements can be the IBHS Fortified Home Hurricane Technical Summary (2019).

    If an alternative roof deck water control approach is used, the base flashing should be sealed to the alternative roof deck water control layer with a full bed of mastic and step flashing and counterflashing should be installed as described above and in the guide Step and Kickout Flashing.

    Where sloping roofs intersect the upper vertical surface of the brick layer enclosing the chimney flue, a cricket or saddle flashing should be installed to redirect rainwater that is draining down the roof slope around the chimney (Figure 3).

    Right – A chimney cricket is installed and flashed to direct rainwater around the chimney.
    Figure 3.  A chimney cricket or saddle flashing is installed to direct rainwater out and around the chimney. (Source: Building Science Corporation.)

    During an earthquake, chimneys are the part of the home most likely to experience damage. In the 1994 Northridge earthquake in Los Angeles, around 15,000 chimneys fell (SFGate 2014). Each of these failures can result in damage to the home, occupants, and the surrounding site. A simple preventative inspection can be taken to assess the risk of chimney failure. 

    Ensuring Success

    The chimney must be adequately tied to the roof framing for structural support in high winds and earthquakes.

    The fundamental principle of waterproofing the connection between the roof assembly and the chimney is to connect the water control layer of the roof assembly to the water control layer of the chimney.

    Metal flashing typically serves as a water control layer transition between the brick layer and the fully adhered roof membrane underlayment. Metal flashing typically has three elements - a base flashing, a step flashing, and a counterflashing. The flashing elements need to be layered in a manner to shed and drain incident rainwater.

    Where sloping roofs intersect the upper vertical surface of the brick layer enclosing the chimney flue, a cricket or saddle flashing should be installed to redirect rainwater that is draining down the roof slope around the chimney.

    Install metal straps on existing masonry chimneys as reinforcement during earthquakes. If a professional engineer instead recommends retrofitting a chimney by capping, remodeling the chimney, or installing an entirely new firebox and chimney, follow their recommendations. 

    Climate

    Hurricane-Prone Areas

    In its Fortified Home program, the Insurance Institute for Building and Home Safety (IBHS) requires that the chimney be adequately connected to the roof framing to prevent the chimney from collapsing or breaking away during high winds. See the CAD tab of this guide for a detail from IBHS that specifies a retrofit method for providing adequate anchorage of an existing chimney to the roof members. IBHS requires that if the chimney is more than 5 feet above the roof, support detailing must be specified by an engineer or licensed design professional. See the IBHS Fortified Home Hurricane Standards (2019) for additional details.

    Waterproofing of the connection between the roof assembly and the chimney is also important for controlling rainwater entry during high wind events such as hurricanes. The fundamental principle of waterproofing the connection between the roof assembly and the chimney is to connect the water control layer of the roof assembly to the water control layer of the chimney.

    In high wind zones shown in Figure 1, a fully adhered roof membrane underlayment should be installed over the roof deck sheathing. This underlayment water control layer needs to be connected to the water control layer of the chimney. The water control layer of a chimney is most commonly the brick layer or other exterior cladding comprising the structural enclosure supporting the chimney flue.

    Hurricane-prone and special wind regions of the United States.
    Figure 1. Hurricane-prone and special wind regions of the United States. (FEMA P-804 2010).

     

    Earthquake-Prone Areas

    In areas at high risk of earthquakes, such as those shown in Figure 2 and in other areas where required by local building code, install metal strapping on existing masonry chimneys or retrofit the firebox, chimney, or both for seismic resistance. 

    Probabilistic Map of the Expected Number of Damaging Earthquakes around the United States.
    Figure 2. Seismic map of the 2018 International Residential Code adapted by FEMA to show Seismic Design Categories in color (Source: FEMA 2020). 

     

    Right and Wrong Images
    Image
    Right – A chimney cricket is installed and flashed to direct rainwater around the chimney
    Right – A chimney cricket is installed and flashed to direct rainwater around the chimney
    Image
    Right – Flashing is installed around chimney, skylight, vents, dormers, in valleys and at eaves
    Right – Flashing is installed around chimney, skylight, vents, dormers, in valleys and at eaves
    Image
    Right - Step flashing along a chimney is integrated in a layered manner with asphalt shingle roofing and topped with counterflashing that is embedded into brick mortar joint above
    Right - Step flashing along a chimney is integrated in a layered manner with asphalt shingle roofing and topped with counterflashing that is embedded into brick mortar joint above
    Image
    Right – There is a properly installed and layered self-sealing bituminous membrane at the roof penetration
    Right – There is a properly installed and layered self-sealing bituminous membrane at the roof penetration
    Image
    Right – Integrate pipe flashing with roof shingles
    Right – Integrate pipe flashing with roof shingles
    Image
    A masonry chimney is shortened and capped at roof level to reduce its chances of detaching in high winds or earthquakes; the fireplace can no longer be used.
    A masonry chimney is shortened and capped at roof level to reduce its chances of detaching in high winds or earthquakes; the fireplace can no longer be used.
    Image
    Chimneys and roof valleys are flashed with metal flashing that is integrated with roof shingles.
    Chimneys and roof valleys are flashed with metal flashing that is integrated with roof shingles.
    Image
    Cross section showing points of reinforcement and attachment to secure the chimney to the roof and ceiling joists.
    Cross section showing points of reinforcement and attachment to secure the chimney to the roof and ceiling joists.
    Image
    How to reinforce a chimney to resist earthquakes and high winds – side and top views.
    How to reinforce a chimney to resist earthquakes and high winds – side and top views.
    Image
    Locations for earthquake anchorage of masonry chimney at exterior house wall.
    Locations for earthquake anchorage of masonry chimney at exterior house wall.
    Image
    This brick chimney was damaged during an earthquake.
    This brick chimney was damaged during an earthquake.
    Image
    This chimney was not adequately attached to the structure and fell away during an earthquake
    This chimney was not adequately attached to the structure and fell away during an earthquake
    Image
    Top view showing how the chimney is attached to ceiling joists that run perpendicular to the exterior wall.
    Top view showing how the chimney is attached to ceiling joists that run perpendicular to the exterior wall.
    Image
    Top view showing how the chimney is attached to at least four ceiling joists running parallel to the exterior wall.
    Top view showing how the chimney is attached to at least four ceiling joists running parallel to the exterior wall.
    Image
    A masonry chimney is reconstructed to withstand seismic forces by completely retrofitting the firebox and chimney using light-frame construction on the top of the foundation
    A masonry chimney is reconstructed to withstand seismic forces by completely retrofitting the firebox and chimney using light-frame construction on the top of the foundation
    Image
    A masonry chimney is reconstructed to withstand seismic forces by maintaining the current firebox but replacing the chimney section with a metal flue and light-weight chimney enclosure.
    A masonry chimney is reconstructed to withstand seismic forces by maintaining the current firebox but replacing the chimney section with a metal flue and light-weight chimney enclosure.
    Videos
    Publication Date
    Author(s)
    Weather Proofing America
    Organization(s)
    Weather Proofing America
    Description
    Video explaining how to correctly install wall-to-roof flashing and kick-out flashing to protect walls from rain water damage.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on pre-construction measurements. Part 1 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on material preparation before construction. Part 2 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on measuring and bending flashing before installation. Part 3 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on installing the base front apron. Part 4 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on installing step sides. Part 5 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on installing the top pan. Part 6 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on installing the front cap flashing. Part 7 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on installing the left side cap flashing. Part 8 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on installing the right side cap flashing. Part 9 of 11.
    Publication Date
    Author(s)
    Ivy Tech ivyVILOS
    Organization(s)
    Ivy Tech ivyVILOS
    Description
    Video from Ivy Tech ivyVILOS giving an in-depth tutorial on how to properly flash a chimney, focusing on installing the top cap flashing. Part 10 of 11.
    CAD
    CAD Files
    Retrofit Tie-Downs to Secure Chimney to Roof Framing
    Retrofit Tie-Downs to Secure Chimney to Roof Framing

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    ENERGY STAR Certified Homes, Version 3/3.1 (Rev. 09)

    ENERGY STAR Certified Homes requires that builders comply with the National Water Management System Builder Requirements which specifies water management details for roofs, walls, foundations, sites, and building materials.

    Please see the ENERGY STAR Certified Homes Implementation Timeline for the program version and revision currently applicable in in your state.

     

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 1 Mandatory Requirements.
    Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
    Exhibit 1, Item 6) Certified under EPA Indoor airPLUS. See the EPA Indoor airPLUS checklist for additional building and site water management requirements.

     

    2009, 2012, 20152018, 2021 International Residential Code (IRC)

    R301.2.1 Wind limitations and design criteria. Buildings shall be constructed in accordance with the wind provisions of this code using the ultimate design wind speed in Table R301.2(1) as determined from Figure R301.2(5)A. Where not otherwise specified, the wind loads listed in Table R301.2(2) adjusted f height and exposure using Table R301.2(3) shall be used to determine design load performance requirements.

    Masonry or concrete chimneys in Seismic Design Category D0, D1, or D2 shall be reinforced. Reinforcing shall conform to the requirements set forth in Table R1001.1 and Section R606.

    Section R1001.3.1 Vertical reinforcing. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars shall be placed between wythes of solid masonry or within the cells of hollow unit masonry and grouted in accordance with Section R606. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys more than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be provided for each additional flue incorporated into the chimney or for each additional 40 inches (1016 mm) in width or fraction thereof.

    Section R1001.3.2 Horizontal reinforcing. Vertical reinforcement shall be placed within ¼ inch (6.4 mm) ties, or other reinforcing or equivalent net cross-sectional area, placed in the bed joints in accordance with Section R606 at not less than 18 inches (457 mm) of vertical height. Two such ties shall be installed at each bend in the vertical bars.

    Section R1001.4 Seismic anchorage. Masonry or concrete chimneys in Seismic Design Category D0, D1, or D2 shall be anchored at each floor, ceiling or roof line more than 6 feet (1829 mm) above grade, except where constructed completely within the exterior walls. Anchorage shall conform to the requirements of Section R1001.4.1

    Section R1001.4.1 Anchorage. Two 3/16-inch by 1-inch (5mm by 25 mm) straps shall be embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor, ceiling, or floor joists or rafters with two 1/2-inch (12.7 mm) bolts.

    Section R1001.4.1.1 Cold-formed steel framing. Where cold-formed steel framing is used, the location where the ½-inch (12.7 mm) bolts are used to attach the straps to the framing shall be reinforced with not less than a 3-inch x 3-inch x 0.229-inch (76 mm x 76 mm x 5.8 mm) steel plate on top of the strap that is screwed to the framing with not fewer than seven No. 6 screws for each bolt.

    Section R1003 Masonry Chimneys

    R1003.3 Seismic reinforcing. Masonry or concrete chimneys shall be constructed, anchored, supported and reinforced as required in this chapter. In Seismic Design Category D0, D1, or D2 masonry and concrete chimneys shall be reinforced and anchored as detailed in Sections R1003.3.1, R1003.3.2, and R1003.3.4. In Seismic Design Category A, B, or C, reinforcement and seismic anchorage are not required.

    R1003.3.1 Vertical reinforcing. For chimneys up to 40 inches (1016 mm) wide, four No. 4 continuous vertical bars, anchored in the foundation, shall be placed in the concrete, or between wythes of solid masonry, or within the cells of hollow unit masonry, and grouted in accordance with Section R608.1.1. Grout shall be prevented from bonding with the flue liner so that the flue liner is free to move with thermal expansion. For chimneys more than 40 inches (1016 mm) wide, two additional No. 4 vertical bars shall be installed for each additional 40 inches (1016 mm) in width or fraction thereof.

    R1003.3.2 Horizontal reinforcing. Vertical reinforcement shall be placed enclosed within ¼-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 joists of unit masonry, at not less than every 18 inches (457 mm) of vertical height. Two such ties shall be installed at each bend in the vertical bars.

    R1003.4 Seismic anchorage. Masonry and concrete chimneys and foundations in Seismic Design Category D0, D1, or D2 shall be anchored at each floor, ceiling, or roof line more than 6 feet (1829 mm) above grade, except where constructed completely within the exterior walls. Anchorage shall conform to the requirements in Section R1003.4.1.

    R1003.4.1 Anchorage. Two 3/16-inch by 1-inch (5 mm by 25 mm) straps shall be embedded not less than 12 inches (305 mm) into the chimney. Straps shall be hooked around the outer bars and extend 6 inches (152 mm) beyond the bend. Each strap shall be fastened to not less than four floor joists with two ½-inch (12.7 mm) bolts.

    R1003.4.1.1 Cold-formed steel framing. Where cold-formed steel framing is used, the location where the 1/2-inch (12.7 mm) bolts are used to attach the straps to the framing shall be reinforced with not less than a 3-inch x 3-inch x 0.229 inch (76 mm x 76 mm x 5.8 mm) steel plate on top of a strap that is screwed to the framing with not fewer than seven N0. 6 screws for each bolt.

    2019 California Residential Code

    In California, all chimneys, both existing and new, are required to be assessed by a government building inspector.

    R1001.3 Seismic reinforcing. Masonry or concrete chimneys in all structures regulated by this code assigned to Seismic Design Category C, D0, D1, or D2 shall be reinforced. Reinforcing shall conform to the requirements set forth in Table R1001.1 and Section R606.

    Retrofit: 

    2009, 2012, 2015, 2018, and 2021 IRC

    Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)

    Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

    Existing Homes

    In its Fortified Home program, the Insurance Institute for Building and Home Safety (IBHS) requires that the chimney be adequately connected to the roof framing to prevent the chimney from collapsing or breaking away during high winds and earthquakes. See the CAD tab of this guide for a detail from IBHS that specifies a retrofit method for providing adequate anchorage of an existing chimney to the roof members. IBHS requires that if the chimney is more than 5 feet above the roof, support detailing must be specified by an engineer or licensed design professional. See the IBHS Fortified Home Hurricane Standards (2019) for additional details.

    Ensuring Chimneys are Adequately Anchored (The following is excerpted from FEMA P-804, 2010, Wind Retrofit Guide for Residential Buildings.)

    If a wood-frame chimney on a home collapses during a high-wind event, significant damage can occur to the home as well as surrounding buildings. Therefore, if a home undergoing a wind retrofit project has a chimney framed with wood, it should be anchored to the structure as part of the continuous load path retrofit so that loads applied to it are transmitted through the load path and adequately resisted. Wood-frame chimneys that are on the interior of the roof and extend 5 feet or less from the roof deck can be retrofitted using prescriptive requirements, described here.

    The following retrofits should be performed on wood-framed chimneys: 1. Tensions straps with a minimum tension capacity of 700lbs. at each end should be fastened to the stud at each corner of the chimney and to the roof framing members below the chimney. 2. Wood structural panels with a minimum nominal thickness of 7/16 inch should be applied to the chimney framing on all sides. 3. Continuous wood blocking supports should be fastened to roof framing members around the base perimeter of the chimney framing using joist hangers. Wood blocking should have minimum dimensions of 2 inches x 4 inches and should be continuous around the chimney framing.

    For more information on this type of solution, consult retrofit programs such as the IBHS FEH program for prescriptive details. If the wood-frame chimney is on the interior of the roof, the entire chimney structure is supported by the roof framing members, which allows the use of the prescriptive solution described above. If the chimney is located along the roof edge, the chimney structure is supported by both roof framing members and a load-bearing wall on the exterior of the building, making a prescriptive retrofit more difficult. Similarly, larger chimneys may require a more detailed and less generic solution to adequately anchor the chimney to the structure. If a chimney extends farther than 5 feet above the roof deck or extends along the roof perimeter, a professional engineer should be consulted to develop a detailed solution. The solution should address the following:

    • Chimney wall framing adequacy
    • Overturning stability and base shear requirement
    • Adequacy and bracing requirements for roof support members
    • Attachment schedule of chimney structure to the roof structure.

    A professional engineer will typically be required to complete the continuous load path retrofit portion of the Advanced Mitigation Package. An engineered solution may involve installing additional metal connectors at the roof level if the side wall framing members are continuous from the bearing wall framing. It may include altering the member size and spacing of roof framing members to support the load from the chimney, installing wood posts at each end of the wall if the chimney side wall framing members start from the top of the supporting wall, or setting posts at the interior side of the wall framing at each corner. A retrofit solution for a masonry chimney will be more difficult than for a wood-frame chimney, and would likely require rebuilding the chimney (at least for the portions above the roof line) (FEMA P-804, 2010).

    Inspect the chimney to verify there is flashing where the chimney intersects with the roof. If flashing does not exist, install flashing as described in this guide, ensuring that it is properly connected to the connection between the roof assembly and the chimney is important for controlling rainwater entry during high wind events such as hurricanes. The fundamental principle of waterproofing the connection between the roof assembly and the chimney is to connect the water control layer of the roof assembly to the water control layer of the chimney. If the exterior cladding of the chimney is brick, step flashing, base flashing, and counter flashing should be installed as described in the Description tab.

    In high wind zones, a fully adhered roof membrane underlayment should be installed over the roof deck sheathing. This underlayment water control layer needs to be connected to the water control layer of the chimney.

    When retrofitting an earthquake-damaged chimney, start by changing the design from the pre-earthquake conditions that caused the failure. FEMA’s ‘Repair of Earthquake-Damaged Masonry Fireplace Chimneys’ describes four retrofit options intended to minimize the risk of future chimney problems. (FEMA 2015). Note that FEMA states it is generally considered infeasible to retrofit chimneys to meet up to date earthquake bracing requirements. (FEMA P-530, 2020). In cases in which a chimney retrofit is feasible, choose one of the four following retrofit options.

    Repair of Earthquake-Damaged Masonry Fireplace Chimneys 2015

    1. Good – Capping of Chimney at Roof Level (Alternative A)

    For a single-story dwelling, if all damage occurred at or above the roof level, the chimney can be permanently removed down to the roof level. This is only possible when use of the fireplace will be discontinued. This is the least costly of the alternatives, but also provides a lesser level of hazard mitigation.

    Exterior appearance: The firebox and chimney will remain unchanged up to the roof level. The upper portion of the chimney will be removed.

    Interior appearance: Fireplace and mantel will remain, but the fireplace can no longer be used and will need to be closed off.

    Environmental: Fireplace can remain fuel-burning (note that the owner could also choose to convert to a more environmentally friendly gas-burning fireplace), although this option would require that a functioning flue be installed or retained through the original chimney.

    A masonry chimney is shortened and capped at roof level to reduce its chances of detaching in high winds or earthquakes; the fireplace can no longer be used.
    Figure 1. A masonry chimney is shortened and capped at roof level to reduce its chances of detaching in high winds or earthquakes; the fireplace can no longer be used (Source: FEMA 2015).

     

    2. Better – Reconstruction from Top of Firebox, Maintaining Existing Fireplace (Alternative B)

    Allows continued use of an undamaged masonry firebox in combination with a new metal flue and light-weight chimney enclosure.

    Exterior appearance: The firebox at the bottom of the chimney will remain exposed brick. The reconstructed portion of the chimney is often finished with siding or stucco, but can also be finished with adhered brick veneer to preserve the original appearance.

    Interior appearance: Remains unchanged.

    Environmental: Fireplace can remain fuel-burning. (Note that the owner could also choose to convert to a more environmentally friendly gas-burning fireplace.)

     A masonry chimney is reconstructed to withstand seismic forces by adding an insert to the existing firebox
    Figure 2. A masonry chimney is reconstructed to withstand seismic forces by maintaining the current firebox but replacing the chimney section with a metal flue and light-weight chimney enclosure (Source: FEMA 2015). 

     

    3. Better – Reconstruction from Top of Firebox, Using Fireplace Insert (Alternative C)

    Allows continued use of an undamaged masonry firebox in combination with a new chimney. In addition, a factory‐built fireplace insert is installed inside of the fireplace.

    Exterior appearance: The firebox at the bottom of the chimney will remain exposed brick. The reconstructed portion of the chimney is often finished with siding or stucco, but can also be finished with adhered brick veneer to preserve the original appearance.

    Interior appearance: Fireplace and mantel will remain, but a fireplace insert will be visible inside of the original masonry fireplace.

    Environmental: Fireplace can remain fuel‐burning. Fireplace inserts can be more energy efficient at producing heat in the home, can reduce emissions through more complete combustion of solid fuels, or can be converted to a more environmentally friendly gas‐burning fireplace.

    A masonry chimney is reconstructed to withstand seismic forces by adding an insert to the existing firebox
    Figure 3. A masonry chimney is reconstructed to withstand seismic forces by adding an insert to the existing firebox (Source FEMA 2015).

     

    4. Best – Full Reconstruction of Firebox and Chimney (Alternative D)

    Involves replacement of the entire firebox and chimney with light‐frame construction above the top of the foundation. This is necessary if earthquake damage extends below the shoulder of the firebox. It is also appropriate where complete removal of fireplace masonry is preferred.

    Exterior appearance: The entire height of the firebox and chimney is reconstructed and is often finished with siding or stucco, but can also be finished with adhered brick veneer to preserve the original appearance. None of the original brick masonry remains.

    Interior appearance: The fireplace and mantel will be removed and replaced with a factory‐built fireplace unit. This can provide an opportunity to change or modernize the interior appearance or enhance the use of the fireplace.

    Environmental: The fireplace can remain fuel‐burning. Factory‐built fireplace units can be more energy efficient at producing heat in the home, can reduce emissions through more complete combustion of solid fuels, or can be more environmentally friendly gas‐burning fireplaces.

    A masonry chimney is reconstructed to withstand seismic forces by completely retrofitting the firebox and chimney using light-frame construction on the top of the foundation
    Figure 4. A masonry chimney is reconstructed to withstand seismic forces by completely retrofitting the firebox and chimney using light-frame construction on top of the foundation (Source: FEMA 2015).

    When examining a chimney structure for potential seismic problems, IBHS recommends checking for severe cracks, described as anything wider than the edge of a dime. These cracks usually occur in the area between the bricks in the mortar. Besides obvious problem areas such as cracks, other potential issues include chimneys that are tall and narrow that will sway and possibly fall or crack during an earthquake. Consider hiring a professional contractor who works on chimneys to shorten the chimney in cases where the structure is too tall. In some cases, chimneys are held to the side of the home using straps. If this is the case, inspect these fastenings for any evidence of rust on the fastenings or poor workmanship, such as large gaps between the fastenings and chimney structure. As with other roof structure components, if you are unsure of what to do, contact a professional engineer to add structural components such as bracing and metal strapping to anchor the chimney properly (IBHS 2001). IBHS recommends reinforcing masonry chimneys in earthquake zones with metal straps as shown in Figure 5 below.

    Chimney retrofit includes metal strap reinforcement at different levels of the home
    Figure 5. Chimney retrofit includes metal strap reinforcement at different levels of the home (Source: IBHS 2001).

     

    California Earthquake Authority gives similar advice to homeowners. Their three reinforcement options are as follows:

    1. Add layers of plywood to the roof around the chimney.

    2. Remove the upper part of the chimney and replace it with metal.

    3. Add a diagonal steel brace to the chimney.

    The upfront cost of retrofitting a chimney to withstand an earthquake can be a barrier for homeowners. Table 1 illustrates that while the project cost of retrofitting a chimney as a preventative measure can be high depending on the specifics of the project, the cost of repairing earthquake damage caused by chimney failure is much higher (SCEC 2021).

    Comparison of costs for preventing vs. repairing earthquake damage from unreinforced masonry chimney failure
    Table 1. Comparison of costs for preventing vs. repairing earthquake damage from unreinforced masonry chimney failure (Source: SCEC 2021). 

     

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    References and Resources*
    Author(s)
    Insurance Institute for Business & Home Safety
    Organization(s)
    IBHS
    Publication Date
    Description
    Webpage providing video links and Spanish/English handouts for installing roofs to meet the hurricane and high wind resistant guidance in the IBHS Fortified Home criteria.
    Author(s)
    Insurance Institute for Business & Home Safety
    Organization(s)
    IBHS
    Publication Date
    Description
    Guide describing the requirements by FORTIFIED Home™ for improving the home's resistance in severe thunderstorms, straight-line wind events, and high winds at the outer edges of tornadoes.
    Author(s)
    Kapur,
    Mahadevia,
    Park,
    Passman,
    Perotin,
    Reeder,
    Seitz,
    Sheldon,
    Tezak
    Organization(s)
    FEMA
    Publication Date
    Description
    Report providing guidance on how to improve the wind resistance of existing residential buildings in Mississippi and across the Gulf Coast.
    Author(s)
    Federal Emergency Management Agency
    Organization(s)
    FEMA
    Publication Date
    Description
    Guide provides homeowners ways to prepare for an earthquake and protect a home against earthquake damage.
    Author(s)
    International Code Council
    Organization(s)
    ICC
    Publication Date
    Description
    Building code for the state of California providing the building rules and regulations as well as disaster resistance tools.
    Author(s)
    Tucker,
    Jill
    Organization(s)
    SFGate
    Publication Date
    Description
    News article from SFGate explaining and giving figures on how chimney failure is the most common type of damage to homes during an earthquake.
    Author(s)
    Southern California Earthquake Center
    Organization(s)
    SCEC,
    University of Southern California
    Publication Date
    Description
    Webpage from Southern California Earthquake Center (SCEC) on identifying key problem spots on unreinforced masonry chimneys and how to retrofit them to withstand seismic forces.
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

    The following authors and organizations contributed to the content in this Guide.

    Building Science Corporation

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