A chimney cricket also called a chimney saddle, is a peaked water-diverting structure built behind a chimney where it intersects a sloped roof. Without a cricket, rainwater, snow, and debris accumulate on the uphill side of the chimney, leading to premature flashing failure, roof leaks, rot, and costly structural damage. Building codes in many regions require a cricket for chimneys wider than 30 inches measured perpendicular to the roof slope. This guide covers everything you need to know about designing, framing, and waterproofing a chimney cricket to ensure a durable, leak-free roof. For a broader understanding of masonry chimney construction, refer to our related guide.
What Is a Chimney Cricket and Why You Need One
A chimney cricket is essentially a small roof ridge installed on the high side of a chimney. It diverts water around the chimney rather than allowing it to pool against the masonry. The cricket acts as a watershed, splitting the flow of rainwater so it runs down either side of the chimney and continues its path down the main roof slope.
The Problem a Cricket Solves
When a chimney penetrates a sloped roof, the uphill side creates a natural dam. Leaves, pine needles, and snow accumulate in this pocket. Over time, standing water against the chimney causes:
- Deterioration of mortar joints from freeze-thaw cycles
- Corrosion of metal flashing and counterflashing
- Rot in the roof sheathing and framing members behind the chimney
- Mold and mildew growth in attic spaces
- Interior water stains and ceiling damage
Building Code Requirements
The International Residential Code (IRC) is clear on chimney crickets. Section R1003.4 states that when a chimney is more than 30 inches wide measured perpendicular to the roof slope, a cricket or saddle must be installed. Some local amendments require crickets for chimneys as narrow as 24 inches, particularly in regions with heavy snowfall. Understanding the relationship between the chimney width and roof pitch is critical for roof framing basics and overall structural planning.
| Chimney Width (perpendicular to slope) | IRC Requirement | Recommended Practice |
|---|---|---|
| Less than 24 inches | No cricket required | Cricket optional but beneficial in snow zones |
| 24 to 30 inches | Check local amendments | Cricket strongly recommended |
| More than 30 inches | Cricket required | Cricket mandatory for code compliance |
| More than 48 inches | Cricket required | Engineered cricket design may be needed |
Design and Sizing Requirements for Chimney Crickets
Proper sizing ensures the cricket sheds water effectively without creating new problems. The dimensions depend on the roof slope and the chimney width.
Determining Cricket Height and Slope
The cricket ridge should be centered behind the chimney and rise from the roof surface at the same pitch as the main roof. The ridge line runs vertically up the center of the chimney face. Key design parameters include:
- Ridge height: The cricket ridge should meet the chimney at or above the highest point of the chimney on the uphill side
- Slope: Match the main roof slope for consistent water shedding
- Width: The base of the cricket should extend at least 12 inches beyond each side of the chimney
- Length: Extend the cricket from the chimney face downslope at least 18 inches or to the next roof framing member
Material Selection
Chimney crickets can be built from several materials depending on the roofing system and aesthetic preferences. Here is a comparison of common options:
| Material | Durability | Cost | Best Application |
|---|---|---|---|
| Copper | 50+ years | High | Historic homes, high-end roofing, soldered seams |
| Galvanized steel | 20 to 30 years | Moderate | Standard residential, painted to match roof |
| Stainless steel | 50+ years | High | Coastal areas, premium installations |
| Aluminum | 15 to 25 years | Low | Budget installations, non-snow regions |
| Built-up roofing | 15 to 20 years | Moderate | Low-slope roofs, modified bitumen systems |
For detailed information about selecting the right cap components, see our article on best materials for chimney caps.
Step-by-Step Framing and Construction
Building a chimney cricket follows a systematic process. The steps below assume the roof sheathing is in place and the chimney is already constructed.
Tools and Materials
Before starting, gather the following:
- Circular saw or jigsaw for cutting sheathing
- Framing square and level for layout
- 2×4 or 2×6 lumber for cricket rafters and ridge board
- Plywood or OSB for cricket sheathing (same thickness as roof sheathing)
- Roofing underlayment (felt or synthetic)
- Flashing materials (copper, galvanized, or prefabricated cricket pan)
- Roofing nails, galvanized fasteners, and sealant
Construction Sequence
Follow these steps in order for a properly built cricket:
- Mark the layout. Snap chalk lines from the chimney corners downslope at 45-degree angles. The intersection of these lines marks the cricket ridge termination. Transfer these lines onto the roof sheathing.
- Cut the roof sheathing. Remove the roof sheathing within the cricket area to expose the rafters below. This allows you to frame the cricket directly into the roof structure.
- Install the cricket ridge board. Cut a ridge board that runs vertically from the chimney face down to the point where the 45-degree lines intersect. The ridge board must be plumb and securely fastened to the roof rafters.
- Install cricket rafters. Cut and install rafters that run from the ridge board to the existing roof rafters on each side. Space them 16 or 24 inches on center matching the roof framing spacing. Each rafter must be cut with a birdsmouth where it meets the existing rafter.
- Install sheathing. Cut plywood or OSB panels to cover the cricket frame. The sheathing should extend to the edges and be nailed securely to all framing members.
- Apply underlayment. Cover the cricket sheathing with roofing underlayment, overlapping the main roof underlayment by at least 6 inches on all sides. This creates a continuous water barrier.
- Install flashing. Step flashing must be integrated where the cricket meets the chimney, and continuous flashing is required along the cricket ridge and valleys. This is the most critical step for preventing leaks.
- Install roofing material. Shingles, metal panels, or other roofing material are installed over the cricket, matching the main roof. Ridge cap shingles go along the cricket ridge.
Critical Framing Details
Pay attention to these details during framing:
- Ensure the cricket slope matches the main roof slope exactly. A mismatch creates an uneven roofline that looks unprofessional and sheds water poorly.
- Use galvanized or stainless steel fasteners to prevent corrosion. Copper flashing requires copper or stainless fasteners to avoid galvanic corrosion.
- Install a minimum 2-inch air gap between the cricket framing and the chimney masonry. This gap satisfies clearance requirements and prevents heat transfer.
- Add blocking between cricket rafters at the chimney face for nailing support for the apron flashing.
Flashing and Waterproofing the Chimney Cricket
Flashing is the most critical part of a chimney cricket. Even a perfectly framed cricket will leak if the flashing is not properly installed. The flashing system consists of several components that work together to direct water away from the chimney-roof intersection.
Components of a Cricket Flashing System
A complete flashing installation requires these elements:
- Base flashing. Also called step flashing, these are individual pieces installed between each course of roofing material along the sides of the cricket. Each piece tucks under the roofing above and overlaps the piece below.
- Apron flashing. A continuous piece of metal installed at the downslope base of the cricket. It directs water onto the main roof surface below the cricket.
- Counterflashing. Metal pieces that are embedded into the chimney mortar joints and bent down over the base flashing. These prevent water from running behind the step flashing.
- Cricket pan. Some builders prefer a pre-formed metal cricket pan that covers the entire cricket before roofing material is applied. This provides a second layer of protection under the finished roofing.
- Cricket ridge flashing. A continuous metal cap along the cricket ridge, often soldered at the top where it meets the chimney.
Proper Flashing Installation Sequence
Install cricket flashing in this order for best results:
- Start with the cricket pan or continuous flashing membrane covering the entire cricket surface. Extend it at least 6 inches up the chimney face.
- Install step flashing up both sides of the cricket, starting at the bottom. Each piece must overlap the one below by at least 2 inches. Nail only the top edge so the lower edge remains free for water runoff.
- Apply counterflashing by cutting grooves into the chimney mortar joints 1 inch deep. Insert the counterflashing and seal with high-grade polyurethane sealant. Bend the counterflashing down over the step flashing.
- Install the ridge cap flashing along the cricket ridge, soldering or sealing joints for continuity.
- Install the apron flashing at the cricket base, extending it at least 4 inches under the roofing material below.
Common Flashing Failures to Avoid
Even experienced roofers make mistakes on cricket flashing. Watch for these common problems:
- Nailing through the exposed face of the flashing. Every nail hole through the visible part of a flashing piece is a potential leak path. Nail only in concealed locations.
- Insufficient overlap. Step flashing pieces must overlap by at least 2 inches. Less overlap allows capillary action to draw water behind the flashing.
- Missing counterflashing. Relying solely on sealant instead of counterflashing is a common shortcut that fails within a few years as sealant degrades from UV exposure.
- Improper cricket-to-chimney intersection. The cricket ridge must extend to the full height of the back of the chimney. If the cricket ridge is too low, water can flow over the top and pool behind the chimney.
- Using incompatible metals. Mixing copper with galvanized steel or aluminum without proper separation causes galvanic corrosion that eats through the flashing in months.
For best results, always maintain proper air sealing between chimney and framing to prevent air leakage, moisture migration, and heat loss at the chimney penetration. A well-sealed framing connection combined with a properly flashed cricket creates a durable, long-lasting roof penetration.
Conclusion
A chimney cricket is an essential roof component for any chimney wider than 30 inches on a sloped roof. Proper design, framing, and flashing ensure that the cricket performs its function for the life of the roof. The key takeaways are: match the cricket slope to the main roof slope, extend the cricket at least 12 inches past each side of the chimney, use compatible corrosion-resistant metals for flashing, and always install counterflashing rather than relying on sealant alone. By following the techniques described in this guide, builders and homeowners can eliminate a common source of roof leaks and extend the service life of both the roof and the chimney structure.