IRC 2024 Chimney Cricket: Required When Chimney Is 30 Inches or Wider

Quick Answer

IRC 2024 Section R903.2.2 requires a cricket or saddle on the uphill (high) side of any chimney that is 30 inches or wider measured perpendicular to the roof slope. A cricket is a small peaked structure built directly against the uphill face of the chimney to divert water and debris around the chimney base rather than allowing them to accumulate there. The cricket must have a ridge height sufficient to shed water away from the chimney, must have a slope at least equal to the adjoining roof slope, and must be flashed and counterflashed using the same methods required for the main chimney flashing.

Under IRC 2024, a chimney without a required cricket is one of the most reliable long-term sources of roof leaks because water and ice collect in the pocket created by the chimney’s uphill face.

What IRC 2024 Actually Requires

Section R903.2.2 establishes the threshold width and the performance standard for crickets, while Section R903.2 governs the flashing requirements that the cricket must satisfy.

Width threshold. A cricket is required when the chimney is 30 inches or greater in width as measured perpendicular to the ridge — meaning the dimension of the chimney that spans across the roof slope. A chimney that is 36 inches wide across the slope requires a cricket. A chimney that is 24 inches wide does not, though many contractors install one anyway for performance reasons. The 30-inch measurement applies to the masonry or metal chimney structure itself, not to the surrounding flashing.

Cricket slope requirement. The cricket must have a slope on each of its two faces that is at least equal to the slope of the main roof. If the main roof is 5:12, the cricket faces must be at least 5:12. In practice, contractors often build the cricket at a steeper slope than the main roof to ensure positive drainage even if minor variations exist in the framing. A flat or nearly flat cricket defeats its own purpose by creating a collection point rather than diverting water.

Cricket construction. The cricket is framed with a central ridge running from the chimney face to the apex of the cricket, and two sloped faces extending to the main roof on each side. The ridge of the cricket meets the uphill chimney face at or near the chimney centerline. Framing is typically dimensional lumber cut to the required angles, sheathed with the same structural panels as the main roof. The cricket becomes a permanent structural element of the roof, not an added-on accessory.

Flashing the cricket. The entire cricket surface must be waterproofed. The cricket meets the chimney on three sides (the uphill face and portions of both side faces), and all three interfaces must be flashed. Step flashing integrates the cricket sides with the main roof courses. The chimney face receives the same counterflashing (reglet-mounted or saw-cut into the mortar joint) as the main chimney flashing below. The cricket ridge typically receives a purpose-made metal cap flashing or a continuous piece of metal bent to cover the ridge and lap onto both faces.

Flashing materials for crickets. Metal flashing at the cricket must meet the same minimum gauge as the general chimney flashing requirement: minimum 26-gauge galvanized steel, 0.019-inch-thick aluminum, or equivalent. Copper is also permitted and is preferred for high-end masonry chimney applications because it is self-healing at joints through the natural patina process. The metal must be compatible with the masonry (copper and aluminum should not contact each other or untreated galvanized in a way that creates galvanic corrosion).

Why This Rule Exists

Chimneys create a disruption in the roof plane. On the uphill side, the chimney acts as a dam — water running down the slope strikes the chimney face and has nowhere to go except to accumulate in the pocket between the chimney base and the roof surface. On wide chimneys, this pocket is large enough to hold significant volumes of water and, in cold climates, to accumulate substantial ice and debris.

Ice in the uphill chimney pocket is a particular problem. Unlike ice dams at the eave, which melt from below as the roof deck warms, the ice in a chimney pocket has direct contact with masonry — which is an excellent thermal conductor and quickly pulls heat from the adjacent structure. The ice expansion and contraction cycles work at the mortar joints and the flashing adhesion points, gradually opening pathways for water infiltration. Even a well-installed flashing system will fail prematurely if it is subjected to the persistent moisture and freeze-thaw cycles of an unprotected chimney pocket.

For chimneys narrower than 30 inches, the pocket is small enough that properly designed and installed chimney flashing can manage the water accumulation. At 30 inches or greater, the pocket becomes too large and the water volume too significant for flashing alone to handle reliably over a 20- to 30-year roofing system life.

Debris accumulation compounds the water problem. Leaves, pine needles, and other debris that blow onto the roof collect in the chimney pocket, retaining moisture against the masonry long after the surrounding roof has dried. This persistent moisture accelerates masonry deterioration and undermines any caulk or sealant at the flashing joint.

What the Inspector Checks at Rough and Final

The cricket is inspected during both the framing stage (structure) and the final roofing inspection (flashing and weatherproofing). Inspectors check:

• Chimney width measured perpendicular to the ridge to determine whether the cricket is required
• Cricket framing structure — central ridge properly aligned with chimney face centerline
• Cricket slope on each face equal to or greater than the main roof slope
• Sheathing on cricket faces continuous with main roof sheathing, no gaps
• Step flashing at the cricket-to-roof intersection on both sides
• Cricket face flashing covering the uphill chimney face and both return faces of the cricket
• Counterflashing bedded in mortar joints or set in reglets at the chimney masonry
• No exposed nail heads or fasteners in the flashing assembly
• Sealant at flashing joints where the code or manufacturer instructions require it

What Contractors Need to Know

Cricket layout requires geometric precision. The ridge of the cricket runs from the center of the uphill chimney face to the apex of the cricket, where it meets a horizontal line extended from the chimney corners along the main roof surface. Getting this geometry wrong produces a cricket that sheds water directly at the chimney corners rather than to the sides, which concentrates flow at the most vulnerable flashing joints.

The cricket ridge cap is one of the most difficult pieces to fabricate and install correctly. It must cover the full cricket ridge from the chimney face out to the main roof surface, lap down both cricket faces without gaps, and integrate with the step flashing at the chimney sides. Custom-bent metal fabricated to the exact cricket ridge angle is far more reliable than attempting to adapt standard off-the-shelf flashing pieces.

Ice and water shield should be applied to the full cricket surface before any metal flashing. On a chimney where the cricket is required (30 inches or greater), the ice dam risk is substantial, and the membrane provides the self-sealing backup layer that standard felt cannot. The membrane is applied first, the metal flashing is installed over it, and the counterflashing is installed last.

Retrofit cricket installation on an existing chimney requires removing a substantial area of shingles — typically several courses above and on both sides of the chimney — to properly frame and flash the cricket. This is a significant project that disturbs much more roofing than it might appear, and homeowners should budget accordingly.

What Homeowners Get Wrong

Many homeowners with leaking chimneys have the leaks attributed to “failed caulk” and have contractors re-caulk the flashing joints as a repair. This is rarely an effective long-term solution. If the chimney is 30 inches or wider and lacks a cricket, the root cause is the water accumulation and ice damage that caulk cannot address. The correct repair is installation of a properly framed and flashed cricket.

Homeowners also sometimes confuse the chimney saddle with a decorative element and are surprised when a contractor says it is required. The cricket is entirely functional — it has no decorative purpose — and its presence or absence is often invisible to the homeowner once roofing and flashing cover it. An inspection report or a roofing contractor’s assessment is typically how homeowners first learn they lack one.

On homes with brick chimneys, homeowners sometimes resist cricket installation because it requires disturbing the brick on the uphill chimney face to set the counterflashing. This concern is legitimate — it requires careful masonry work — but it does not change the code requirement. The counterflashing must be properly bedded or mechanically attached to the masonry, not just surface-caulked.

State and Local Amendments

Some cold-climate jurisdictions have adopted a lower width threshold for cricket requirements, triggered at 24 inches rather than the IRC’s 30 inches, reflecting the more severe ice accumulation conditions in areas with heavy snowfall. Minnesota and Wisconsin have jurisdictions that have made this adjustment in their state-level amendments.

California’s Title 24 energy code intersects with chimney cricket requirements in the context of chimney caps and top dampers for energy efficiency. The cricket itself is still governed by the structural code, but its interaction with chimney energy provisions can complicate the full scope of chimney work in California.

Local historic preservation requirements in older neighborhoods can restrict the modification of visible chimney masonry, potentially creating a conflict between the cricket counterflashing requirement and a historic overlay that limits saw-cutting of mortar joints. In these cases, an alternative flashing method using surface-mounted reglets with mechanical attachment may be acceptable with approval from both the building department and the historic preservation board.

When to Hire a Professional

Cricket installation is not DIY-appropriate for most homeowners. It requires carpentry skill to properly frame the cricket geometry, roofing skill to integrate the flashing system, and masonry skill to set counterflashing in the chimney. All three disciplines must be executed correctly or the cricket will fail to perform its function. A roofing contractor experienced with chimney work should handle the installation, and the masonry counterflashing should be done by or reviewed by a mason.

Any chimney that has a history of leaks on the uphill side should be evaluated by a roofing inspector or contractor before simply re-caulking. If the chimney is 30 inches or wider, the evaluator should document whether a cricket is present and, if not, whether the absence is the root cause of the chronic leak.

Common Violations Found at Inspection

• No cricket on a chimney that is 30 inches or wider perpendicular to the slope, even where the flashing otherwise appears adequate
• Cricket slope less than the main roof slope, creating a near-flat cricket that collects rather than sheds water
• Cricket ridge misaligned with the chimney face centerline, directing flow to one side rather than diverting symmetrically
• Step flashing missing at the cricket-to-roof intersection on the chimney sides
• Counterflashing surface-caulked rather than embedded in mortar or set in a reglet, making it subject to caulk failure
• Exposed fastener heads in the cricket flashing assembly, particularly at the cricket ridge cap
• No ice and water shield under the metal flashing on the cricket surface in cold-climate jurisdictions
• Cricket framed with inadequate sheathing or no sheathing, creating a soft surface that allows metal flashing to deform under foot traffic or debris loading