In fireplace and chimney construction, a “chase” is the enclosure that surrounds a flue or chimney pipe. It can be a freestanding masonry shaft, a framed box built from wood or metal studs, or an exterior-clad column that hides and protects a single-wall or class-A metal flue. Wherever a flue penetrates a roof or passes through living space, a chase provides the visible and structural body around that flue — carrying it from the appliance (firebox or stove) up to the roof termination — while allowing for insulation, ventilation, weatherproofing, and finished exterior treatments such as siding, brick veneer, or stone.
Functionally, a chase is more than mere cladding. It creates the necessary space and support for the flue system, maintains clearances from combustible building materials, and provides a route for attaching flashing, caps, and crown assemblies that keep water and animals out. In factory-built or prefab installations, the chase usually contains a metal chimney pipe and must be built to manufacturer specifications for clearances, insulation, and firestopping. In masonry chimneys, the masonry itself forms the chase around the flue liner and contributes to the chimney’s structural stability and thermal mass.
A chase also plays an important role in performance and longevity. Proper ventilation and a weather-tight chase top and cap prevent moisture intrusion, which is a leading cause of deterioration (rot, rust, mortar failure, and flue liner damage). Correctly constructed chase components — including chase covers, flashing, and proper sealing around roof penetrations — reduce drafts and heat loss, help control creosote buildup by preserving draft conditions, and keep the system safe. Because chases interact with building structure, combustion safety, and code requirements, their design and construction are subject to local building codes and manufacturer instructions.
Understanding what a chase is and how it’s used sets the stage for safe, efficient fireplace and chimney installations. Whether you’re dealing with a brick chimney or a metal flue framed into a chase, attention to framing, clearances, moisture protection, and finishing details determines both the performance of the chimney and the health of the surrounding structure — making the chase a critical element of any chimney system.
Definition and types of chases
A chase is the enclosure or framed structure that surrounds and supports a chimney flue or factory-built (metal) chimney, providing both a finished architectural appearance and protection for the flue system. In practice a chase can be a full masonry stack built of brick, stone, or concrete block that contains the flue liner, or it can be a framed (wood or metal studs) enclosure clad in siding, stucco, or masonry veneer that contains and conceals a prefabricated metal chimney pipe. The chase serves functional roles—protecting the flue from the weather, preventing animal entry, and anchoring flashings and caps—while also meeting aesthetic goals so the chimney blends with the building exterior.
There are several common chase types and configurations. Masonry chases are solid, heavy structures that can be integral to a masonry chimney and are typically made from brick, block, or stone with a masonry flue liner; they are durable and have thermal mass that affects heat transfer. Framed chases are built around factory-built metal chimneys or double-wall flue pipes; these are constructed from framing members and sheathed with noncombustible or combustible exterior finishes (the latter require proper thermal barriers and clearances). Chases can also be classified by location: interior chases inside the building envelope, which reduce freeze/condensation risks, and exterior chases that are exposed to weather and need careful flashing, caps, and insulation considerations. Additional components related to chases include chase covers (top plates that shed water) and chase caps that prevent water and debris from entering the flue opening.
In fireplace and chimney construction the chase is used to maintain required clearances between the heat-producing flue and any combustible framing, to provide anchorage and support for the flue assembly, and to create a weatherproof transition where the flue exits the roof or wall. Properly designed chases incorporate noncombustible materials or specified clearance spaces per manufacturer instructions and building codes, as well as flashing and a secure chase cap to prevent water intrusion, which is a leading cause of chimney deterioration. When a metal flue passes through an exterior chase, designers must also address ventilation and insulation to limit condensation and corrosion; when the chase is part of a masonry system, the chase geometry and liner placement affect draft and heat transfer. For safety and longevity, chase construction must follow manufacturer specifications and local codes, and chases require periodic inspection and maintenance of caps, flashing, cladding, and any sealants.
Materials and construction methods
A chase is the framed or masonry enclosure built around a fireplace flue or factory-built chimney to conceal, protect, and finish the vertical run of the venting system. In fireplace and chimney construction it serves both functional and aesthetic roles: it creates the visible exterior surface (brick, stucco, siding, metal panels), protects the flue from weather and mechanical damage, and provides the required spatial separation between the hot flue and surrounding combustible building materials. Chases are used with masonry chimneys and with prefabricated (factory-built) chimneys; in the latter case the chase hides the double- or triple-wall insulated pipe while also accommodating any required clearances, ventilation or plenums specified by the chimney manufacturer.
Common materials for chases combine structural framing, noncombustible inner linings where needed, and durable exterior claddings. Typical framed chases use conventional wood stud framing or light-gauge steel studs tied into the structure, sheathed with exterior-grade plywood or OSB for structure and then finished with brick veneer, stucco, fiber-cement siding, metal panels, or painted trim. Where the flue passes close to the chase interior, noncombustible linings such as cement board, Type X gypsum, or other code-approved fire-resistant sheathing are used to maintain safe separation from combustible framing. Insulation inside the chase — if provided for energy reasons — is normally noncombustible (mineral wool) and is placed in a manner that does not reduce required clearances around the flue; in many designs the chase is ventilated or has an airspace to allow heat dissipation. Chase tops, caps, and flashing are typically metal (galvanized steel, stainless, or copper) and are crucial for shedding water and preventing moisture intrusion around the chimney termination.
Construction methods vary with whether the chase is freestanding, attached, masonry, or framed for a factory-built chimney. For framed chases the usual approach is to establish a secure supported base or footing, build a stud enclosure sized to provide the required clearances to the flue, install appropriate fire-resistant sheathing on the interior faces, flash and cap the top of the chase to prevent water entry, and finish the exterior with the chosen cladding. Masonry chases and full masonry chimneys require proper footing, through-wall supports, mortar joints, flashing integration where they intersect with roofing, and a flue liner sized to the appliance. In both systems, special attention is given to: anchoring and bracing the chase to resist wind and seismic loads; installing a weatherproof cap and crown; providing access for inspection and maintenance; and following the chimney/flue manufacturer’s installation instructions and local building codes for clearances, fasteners, and materials.
Integration with fireplace, chimney, and flue systems
A “chase” in fireplace and chimney construction is the framed and often enclosed shaft that surrounds and supports a chimney or flue assembly as it passes through a roof or the exterior of a building. Chases are used with both masonry chimneys and prefabricated metal (factory-built) chimney systems; their job is to provide a neat exterior enclosure, maintain required clearances to combustible framing, and protect the flue from weather and moisture. A properly built chase includes features such as a sloped chase top or crown, a metal chase cover or cap to shed water, flashing where the chase meets the roof, and internal firestops or clearance spacers around the flue. The chase therefore serves dual roles: aesthetic/architectural concealment and functional protection/clearance for the flue system it contains.
Integrating a chase with the fireplace, chimney, and flue systems requires careful attention to how the flue connects to the firebox and how chimney components transition through framed construction. For masonry systems this means the chase must accommodate the masonry flue or flue tile and allow for the thickness of any required insulation or airspace. For factory-built chimneys the chase dimensions must match the manufacturer’s specified clearances to combustibles and support/anchor the chimney sections and roof penetration components. The chase also must permit proper connection of the smoke chamber, throat, and flue connector, and provide access for chimney caps, storm collars, and termination assemblies. Where multiple flues or vents run through a single chase, separation and firestopping between flues are critical to prevent heat transfer and to maintain safe clearances.
Performance and safety considerations drive many of the practical integration details. Weatherproofing is essential: poorly flashed chases or missing chase covers invite water into the chimney system, accelerating corrosion of metal liners, promoting creosote accumulation, and causing mortar and masonry deterioration. Firestops, clearances, and noncombustible linings (where required by code or manufacturer) protect surrounding framing from excessive heat; ventilation or drainage provisions in the chase prevent trapped moisture. Proper sealing around flue penetrations and careful adherence to manufacturer instructions and local building code requirements preserve draft, prevent smoke or carbon monoxide leakage into living spaces, and reduce the risk of chimney fires. Regular inspection access built into the chase simplifies cleaning and maintenance, which are essential to the long-term safe operation of the integrated fireplace, chimney, and flue system.
Fire safety, clearances, and building code requirements
A chase is the framed enclosure that surrounds and conceals a flue or factory-built chimney run through a building; it can be an exterior boxed shaft or an interior framed cavity. In fireplace and chimney construction a chase provides a finished architectural appearance and weather protection for the flue while also accommodating flashing, a cap, and termination details. Chases can be built of wood framing with exterior cladding or of noncombustible materials; when they enclose a hot flue the design must either maintain the required airspace between the flue and combustible framing or use listed chase-liner systems and insulation specified by the flue manufacturer to prevent heat transfer to surrounding building elements.
Fire safety and clearances are the core functional requirements for any chase. The flue or chimney system must be kept the required distance from combustible materials, or the chase interior must be constructed of approved noncombustible materials or incorporate the manufacturer’s listed clearance-reduction methods (such as thermal shields or insulating liners). Fireblocking and draft-stopping between floors and around the chase are necessary to slow the spread of fire and smoke, and chase tops and caps must prevent ember penetration and shed water while allowing proper draft and venting. Additionally, clearances around hearths, mantels, and nearby combustibles, plus safe distances to roof edges, operable windows, and property lines, are part of the fire-safety considerations tied to chase placement and design.
Building codes require that chimneys, flues, and their chases be installed in accordance with the chimney and appliance manufacturer’s listing and the applicable local code provisions; this typically means permitting, inspection, and adherence to specified materials and clearances. Codes address structural framing, flashing and weatherproofing of chases, termination heights, spark arrestors, access for inspection/cleaning, and the use of approved firestops and chase linings. Because requirements vary by jurisdiction, fuel type, and chimney system (masonry versus factory-built), installers should follow the appliance and chimney manufacturer’s instructions and obtain the required inspections and permits; routine maintenance—keeping the chase weather-tight, repairing damaged firestops or linings, and ensuring the cap and flashing function—helps preserve fire safety and code compliance over the life of the system.
Inspection, maintenance, and repair considerations
Inspections should be scheduled regularly and whenever something unusual occurs (e.g., strong drafts change, smoke spillage, a chimney fire, or after major storms). A basic annual inspection by a qualified chimney professional will identify common problems such as creosote buildup inside the flue, blockages from nests or debris, cracked or missing mortar in masonry, deteriorated flue liners, corroded metal components, and water damage to the chimney crown, flashing, or chase top. Inspectors use progressively more invasive levels of inspection when there are signs of problems: a simple visual check can suffice for routine maintenance, while evidence of damage or modification may require more detailed camera inspections or removal of finishes to examine concealed components.
A chase is the framed enclosure that surrounds and hides a flue or prefabricated metal chimney on the exterior of a structure. Chases are common with factory-built fireplaces and metal chimney systems where the visible box-like or column form provides a finished exterior that matches the house. Proper chase construction must maintain required clearances to combustibles, include firestopping where the chase passes floors or roof planes, and incorporate weatherproofing features: a secure chase top or cover, slope and seal on the chase crown, durable flashing at roof penetrations, and venting or drainage provisions to avoid trapped moisture. If the chase contains a metal flue, inspection should pay careful attention to corrosion or separation of metal panels and to the integrity of the chase top/cover that prevents water entry.
Maintenance and repair priorities are safety and water management. Creosote removal (sweeping) reduces ignition risk, while repairing or relining a damaged flue restores safe containment of combustion products. Masonry repointing, crown and flashing repair, and replacement or resealing of chase covers and siding stop water intrusion that accelerates deterioration. Any structural repairs that affect the flue or its clearances, or any evidence of heat or combustion damage (for example after a chimney fire), should be handled by trained professionals and may require a Level 2 or 3 inspection. Keeping a record of inspections and repairs, addressing small issues promptly, and using qualified technicians for cleaning and structural repairs will extend the life of the system and reduce fire, water, and carbon-monoxide hazards.