Chimney Flashing Code in Georgia

IRC R903.2 Chimney Flashing Requirements

Georgia regulates chimney flashing through the International Residential Code (IRC), adopted with state-specific amendments by the Georgia Department of Community Affairs (DCA). Section R903.2 establishes the general requirement: flashing must be installed at all wall and roof intersections, at all changes in roof slope or direction, and around all roof penetrations. A chimney creates both a roof-to-wall intersection and a roof penetration, triggering R903.2 on all four sides.

Section R903.2.2 adds the cricket requirement. Any chimney that measures more than 30 inches wide (measured perpendicular to the roof slope) must have a cricket (saddle) constructed on the upslope side. The cricket diverts water around the chimney rather than allowing it to pool against the masonry face. This pooling is the primary cause of chimney leaks on homes without crickets.

The code requires flashing to be "approved corrosion-resistant material." It does not specify a single material. Lead, copper, galvanized steel, aluminum, and stainless steel all satisfy the requirement when the material gauge meets industry standards. The code also requires that flashing be "installed in a manner that prevents moisture from entering the wall or roof." This performance-based language gives contractors flexibility in method while holding them accountable for the result.

Local jurisdictions in Alpharetta, Buckhead, Sandy Springs, Marietta, Roswell, and Johns Creek enforce R903.2 during the final roof inspection. Building inspectors check for the presence of step flashing at sidewalls, apron flashing at the front face, counter flashing over the base layer, and a cricket on chimneys wider than 30 inches. Missing or improperly installed components will fail the inspection.

For a broader overview of Georgia's roofing code framework, see our Georgia residential roofing code guide. For the general roof flashing code that applies to all penetrations and intersections, see our dedicated flashing code page.

Base Flashing and Counter Flashing: The Two-Part System

Chimney flashing uses a two-part system that allows the roof structure and the chimney structure to move independently without breaking the weather seal. This is the critical design principle that separates proper chimney flashing from the single-layer sealant approaches that fail within a few years.

Why Two Parts?

A roof and a chimney are two separate structures that expand, contract, and settle at different rates. The roof framing moves with temperature changes, wind loading, and moisture absorption. The chimney masonry moves with its own thermal cycle and with ground settlement. A single piece of flashing attached to both structures will fatigue and crack at the junction where movement concentrates. A two-part system accommodates this differential movement by allowing each layer to slide against the other.

Base Flashing (Step Flashing at Sidewalls)

Step flashing consists of individual L-shaped metal pieces, each measuring at least 4 inches by 4 inches (4 inches up the chimney face and 4 inches across the roof surface). Each piece integrates with one shingle course. The bottom leg extends under the shingle and over the shingle below. The vertical leg extends up the chimney face. Each step flashing piece overlaps the one below by at least 2 inches, creating a stair-step pattern that directs water away from the chimney at every shingle course.

At the front (downslope) face of the chimney, an apron flashing replaces step flashing. The apron is a continuous piece of metal that spans the full width of the chimney front, with a vertical leg extending up the chimney face and a horizontal leg extending under the shingle courses. The apron must overlap the roof surface by at least 4 inches and extend at least 4 inches up the chimney face.

Counter Flashing

Counter flashing covers the top edges of the step flashing and apron flashing. It mounts to the chimney itself, with the top edge embedded in a mortar joint (reglet) or secured with a surface-mounted receiver. The bottom edge overlaps the base flashing by at least 2 inches. Counter flashing directs water that runs down the chimney face over the base flashing rather than behind it.

Flashing Component	Location	Minimum Dimensions	Attachment
Step flashing	Chimney sidewalls	4" x 4" L-shape, 2" overlap	Nailed to roof deck (not chimney)
Apron flashing	Chimney front (downslope)	4" up chimney, 4" on roof	Nailed to roof deck
Counter flashing	Over step and apron flashing	2" overlap over base flashing	Embedded in mortar joint or surface-mounted
Back pan	Chimney rear (upslope)	Full chimney width, 4" up chimney	Integrated with cricket

"Masonry expands at 0.0004 inches per foot per 100 degrees F. Wood framing moves at different rates. A single piece of flashing cracks at that junction within 3 to 5 years. The two-part system accommodates differential movement."

Cricket Requirements for Chimneys Over 30 Inches Wide

IRC R903.2.2 requires a cricket (also called a saddle) on the upslope side of any chimney wider than 30 inches measured perpendicular to the roof slope. The cricket is a small peaked structure that diverts water around the chimney rather than allowing it to pool against the back face. Without a cricket, water accumulates behind wide chimneys, backs up under shingles, and penetrates the roof deck.

Cricket Construction

A cricket consists of a plywood or OSB deck framed to create a ridge running from the chimney face toward the roof ridge. The ridge height must be sufficient to prevent water from overtopping the cricket during heavy rain. Industry practice sets the ridge height at a minimum of one-half the chimney width, measured from the roof surface at the chimney face.

The cricket deck must be covered with the same roof covering as the rest of the roof (asphalt shingles) or with sheet metal. On most metro Atlanta residential roofs, sheet metal crickets provide better performance because the small surface area and steep angle of a cricket make shingle application difficult and prone to failure. A sheet metal cricket fabricated from the same material as the valley and counter flashing creates a seamless water-shedding surface.

When Crickets Are Needed

Most masonry chimneys on metro Atlanta homes measure 36 to 48 inches wide, well above the 30-inch trigger. A standard fireplace chimney with a single flue typically measures 36 inches. A chimney with two flues may reach 48 inches or wider. Prefabricated metal chimney chases can measure anywhere from 24 to 48 inches depending on the unit.

The 30-inch threshold is not optional. An inspector who measures a chimney at 31 inches and finds no cricket will fail the inspection. The contractor must construct a cricket, reflash the back of the chimney, and schedule a re-inspection before the permit can close.

Cricket Flashing Integration

The cricket integrates with the chimney flashing system through a back pan that extends from the cricket ridge to the chimney face, then up the chimney face by at least 4 inches. Counter flashing covers the top edge of the back pan, just as it covers step flashing at the sidewalls. The cricket sidewalls connect to the step flashing on each chimney side, creating a continuous waterproof envelope from the front apron, along both sides, across the cricket, and back to the sidewall step flashing.

The junction between the cricket and the main roof surface requires the same ice and water shield treatment as a valley. Water concentrates at these junctions and flows at high velocity during heavy rain. A 36-inch-wide ice and water shield membrane centered on each cricket-to-roof junction provides the secondary waterproofing layer that protects the deck if the metal flashing ever fails.

Flashing Material Compatibility and Selection

The IRC requires chimney flashing to be "approved corrosion-resistant material" but does not mandate a specific metal. Material selection depends on the chimney construction, the roof covering, the local climate, and the project budget. Mixing incompatible metals creates galvanic corrosion that destroys the flashing within a few years.

Common Chimney Flashing Materials

• Lead: The traditional chimney flashing material. Lead conforms to irregular masonry surfaces without tools, making it ideal for step flashing against rough brick. Minimum thickness: 2.5 pounds per square foot (approximately 0.040 inches). Lead resists corrosion in Georgia's climate and lasts 50+ years. Environmental regulations have restricted lead use in some jurisdictions, though Georgia code still permits it for residential roofing applications.
• Copper: Premium flashing material that develops a green patina over time. Minimum weight: 16 oz per square foot (approximately 0.0216 inches). Copper lasts the life of the structure. It is the standard choice for high-end homes in Buckhead and Sandy Springs where the patina becomes an architectural feature.
• Galvanized steel: The most common residential chimney flashing material. Minimum gauge: 26 (0.0179 inches). The zinc coating provides corrosion resistance for 20 to 30 years in Georgia's climate. Cost-effective and available in pre-bent profiles.
• Aluminum: Lightweight and corrosion-resistant. Minimum thickness: 0.019 inches. Aluminum must never contact concrete or mortar without a barrier, as the alkaline environment corrodes aluminum. A bituminous coating or separation membrane prevents contact corrosion.

Galvanic Corrosion

When two dissimilar metals contact each other in the presence of moisture, the more active metal corrodes. This galvanic corrosion destroys flashing far faster than normal weathering. The most common problem in metro Atlanta: aluminum flashing touching copper gutters, or galvanized steel flashing touching lead counter flashing. Contractors must use compatible metals or install dielectric barriers between incompatible metals.

Material	Compatible With	Incompatible With	Service Life
Lead	Copper, stainless steel	Aluminum, galvanized steel	50+ years
Copper	Lead, stainless steel	Aluminum, galvanized steel	75+ years
Galvanized steel	Aluminum (with barrier)	Copper, lead	20 to 30 years
Aluminum	Galvanized steel (with barrier)	Copper, lead, concrete	25 to 40 years

Sealant vs. Mechanical Attachment

Sealant alone does not constitute chimney flashing. Roofing cement, silicone caulk, and polyurethane sealant are supplementary materials that seal seams and joints within a mechanically attached flashing system. A contractor who applies sealant over the roof-to-chimney junction without installing step flashing, counter flashing, and (where required) a cricket has not flashed the chimney to code.

Sealant-only "repairs" are the most common deficiency on existing metro Atlanta chimneys. The sealant deteriorates within 2 to 5 years, cracks, pulls away from the masonry, and allows water behind it. The homeowner notices staining on the ceiling near the chimney and calls for a repair. The contractor arrives to find no actual flashing system under the failed sealant. At that point, the proper repair is a full two-part flashing installation, not another layer of sealant.

Why Chimney Leaks Are the Number One Roofing Callback

Chimney flashing involves more components, more material transitions, and more potential failure points than any other roof detail. A single chimney requires step flashing on two sides, an apron at the front, a cricket (or back pan) at the rear, counter flashing on all four sides, and integration with the underlayment and ice barrier system. Each junction between components is a potential water entry point.

Top Chimney Flashing Failure Modes

• Missing counter flashing: Without counter flashing, water running down the chimney face flows behind the step flashing and enters the roof system. This is the most common deficiency found during roof repair inspections.
• Counter flashing not embedded in mortar: Surface-mounted counter flashing sealed with caulk pulls away from the chimney face as the sealant deteriorates. Embedding the counter flashing in a mortar joint (reglet) provides a mechanical anchor that resists pullout for the life of the flashing.
• Missing cricket on wide chimneys: Water pooling behind a wide chimney backs up under shingles during every rain event. This persistent moisture rots the deck, grows mold in the attic, and stains the ceiling below.
• Single-piece flashing instead of step flashing: A single L-shaped piece running the full length of the chimney sidewall cannot accommodate the shingle course pattern. Water enters between the flashing and the shingles at every course line.
• Incompatible metals: Galvanic corrosion between dissimilar flashing metals creates holes in the flashing within 5 to 10 years. The corrosion often starts at concealed contact points and progresses before the homeowner notices leaking.

"Polyurethane sealant on a chimney junction degrades in 2 to 5 years under Georgia's UV exposure and thermal cycling. A mechanically attached two-part flashing system lasts 20 to 30 years because it sheds water instead of trying to block it."

For homeowners in Johns Creek, Roswell, and Alpharetta, chimney condition affects both insurance coverage and resale value. An insurance adjuster who finds deteriorated chimney flashing during a storm damage claim may attribute the leak to pre-existing conditions rather than storm damage, reducing your payout. A home inspector who finds deficient chimney flashing during a sale creates a negotiation item that costs the seller thousands. Code-compliant flashing protects against both scenarios.

How 1 Source Installs Chimney Flashing

Every roof replacement that 1 Source Roofing performs includes a full two-part chimney flashing system. We do not reuse old flashing. We do not apply sealant over existing flashing and call it done. We install new step flashing, new counter flashing, and a new cricket (where required) on every chimney, using materials compatible with the chimney construction and the roof covering system.

Our Chimney Flashing Sequence

Step 1: We remove all existing chimney flashing down to bare masonry and bare deck. Step 2: We install ice and water shield membrane around the full perimeter of the chimney, extending at least 24 inches from the chimney face on all sides. Step 3: On chimneys wider than 30 inches, we frame and sheath the cricket, then cover it with sheet metal. Step 4: We install step flashing at both sidewalls, integrating each piece with its corresponding shingle course. Step 5: We install the apron flashing at the front face. Step 6: We cut reglets into the mortar joints and embed counter flashing on all four sides. Step 7: We seal all reglet cuts and counter flashing top edges with polyurethane sealant as a secondary seal.

Material Selection

We select flashing material based on the chimney construction and the homeowner's preferences. Galvanized steel is our standard for most residential projects. For premium homes in Buckhead and Sandy Springs, we offer copper flashing that develops a distinctive patina and lasts the life of the structure. We verify material compatibility across all components before fabrication begins.

For detailed information about our chimney flashing installation process, materials, and techniques, see our chimney flashing installation guide. For general roof flashing installation services across metro Atlanta, see our flashing services page.

Related Building Code and Technical Guides

These pages cover related code requirements and technical installation standards for Georgia residential roofing:

• Georgia Residential Roofing Code Guide:Complete overview of IRC Chapter 9, permits, and inspections
• Roof Flashing Code Requirements:IRC R903.2 flashing materials, methods, and penetration details
• Valley Flashing Code Requirements:Open valley, closed valley, and metal requirements under IRC R905.2.8.2
• Ice Barrier and Ice Dam Code:IRC R905.1.2 ice barrier requirements and ASTM D1970 membrane specs
• Drip Edge Code Requirements:IRC R905.2.8.5 material specs and installation sequence
• Roof Underlayment Code Requirements:Underlayment standards, synthetic vs. felt
• Skylight Installation Code:Flashing and glazing requirements for skylights
• Chimney Flashing Installation Guide:Step flashing, counter flashing, and cricket construction
• Roof Flashing Installation Atlanta:Professional flashing services for metro Atlanta

Questions about chimney flashing on your home? Call 1 Source Roofing at (404) 277-1377 for a free roof inspection and chimney flashing evaluation.