A chimney cricket is a small, peaked (saddle-shaped) structure built into the roof on the uphill side of a chimney. Its one job is to divert the water, snow, and debris flowing down the slope so it runs around the chimney rather than damming up behind it. If your chimney is wide and sits partway down a sloped roof, everything running downhill hits the back wall and pools there, working under shingles and into the masonry joint. A cricket splits that flow into two streams and carries it past the corners. On many homes a cricket is not optional trim, it is required by code.
What a chimney cricket is (and how it differs from flashing)
A cricket is a miniature ridged roof, framed and sheathed or formed from metal, that ties into the roof deck behind the chimney and rises to a peak against the back wall. That peak acts like the prow of a boat: water arriving from uphill is split and steered down both sides, past the chimney corners, and back onto the open roof below.
This is a different job from flashing. Flashing is the layered metal that seals the seam where the chimney meets the roof so water cannot slip into the joint. A cricket works one step earlier by changing where the water goes before it ever reaches that seam. The two work together on a wide chimney: the cricket keeps runoff from ponding, and flashing (with counterflashing let into the mortar) seals the junction. Our chimney flashing service covers that sealing work; this page is specifically about building the diverter that keeps water from collecting in the first place.
Who actually needs one
A cricket earns its place in a few clear situations:
- Wide chimneys on a slope. The wider the chimney and the steeper the roof, the more water piles against the uphill face. Roughly 30 inches of width across the slope is the common code threshold.
- Chronic leaks at the back wall. If your chimney has been re-flashed or re-sealed and still leaks on the uphill side, the real problem is often standing water that no sealant can hold back for long.
- Debris and staining behind the chimney. A pile of needles, grit, and dark staining collecting behind the stack is a sign water and debris are damming there instead of moving past.
- Rotting deck or shingles behind the stack. Soft sheathing, curling shingles, or granule loss concentrated on the uphill side points to repeated pooling.
A narrow chimney near the ridge, where little roof sits above it, usually does not need one. Diagnosing which case you are in is part of the on-site visit; width, slope, and where the chimney sits on the roof all factor in.
Signs you may need a cricket
- Water stains on the ceiling or wall near an interior chimney chase, especially after heavy rain.
- A leak that returns every wet season no matter how many times the flashing gets caulked.
- Visible ponding, moss, or a debris line along the back of the chimney.
- Deteriorating brick or crumbling mortar concentrated on the uphill face.
These same symptoms can come from a failed cap, a cracked crown, or worn flashing, so the source has to be confirmed on the roof. We do not diagnose a leak sight-unseen. Two useful reads while you wait: Chimney leak: cap, crown, or flashing? and Why does my chimney leak when it rains?
What to expect from the installation
Every cricket starts with an on-site assessment: we measure the chimney width, read the roof slope, and confirm the leak is coming from pooling behind the stack rather than the cap, crown, or an existing flashing failure. From there the work generally involves framing or forming the saddle to the correct pitch, sheathing it where framed, and integrating it with new step flashing and counterflashing so the cricket and the roof-to-chimney seam become one continuous water path. The finished surface is tied into the surrounding roofing and the whole assembly is checked to shed cleanly.
Because a cricket ties into both the roof system and the chimney, scope and cost vary with chimney width, roof pitch, roofing material, and how much surrounding flashing or decking needs attention. We give you a written scope after we have seen the roof rather than a number over the phone. To understand the moving parts, our guide on what chimney leak repair costs walks through the variables. Request a quote and we will lay out exactly what your roof needs.
Why this is professional work
A cricket has to be pitched correctly, tied into the roof deck, and flashed as an integrated system, or it simply moves the leak somewhere else. It also involves roof access and roofing integration, which is not safe DIY. Getting the water management, the flashing laps, and the counterflashing into the mortar right is what separates a cricket that ends a leak from one that hides it for a season.
Why it matters in the Puget Sound climate
Greater Seattle gives a chimney a long, wet season, and steady rain is exactly the condition that exposes a missing cricket. Instead of a few dramatic storms, the masonry behind a wide chimney sits under weeks of runoff, so a spot that ponds even slightly stays saturated. Add the freeze-thaw cycles at higher elevations around the Sound and that trapped water works into mortar joints and brick faces. A cricket that keeps the uphill wall draining is one of the more effective long-term defenses a wet-climate chimney can have.
Frequently Asked Questions
Is a chimney cricket the same as flashing?
No. Flashing is the metal that seals the seam where the chimney meets the roof. A cricket is a peaked structure built behind the chimney that diverts runoff around it before it reaches that seam. On a wide chimney the two are installed together, but they do different jobs.
How wide does my chimney have to be to need a cricket?
The common code threshold under the International Residential Code is a chimney wider than 30 inches measured across the roof slope. Width is not the only factor, though; roof pitch and where the chimney sits on the slope also matter, so the call is made on-site.
Can a cricket be added to an existing roof, or only during a reroof?
It can be added to an existing roof. It is often most efficient to install one during a reroof, but a cricket can be built and integrated with new flashing on a roof that is otherwise staying in place. We confirm the best approach after seeing the roof.
My flashing keeps getting sealed but the chimney still leaks on the back side. Why?
That is a classic sign the real problem is water pooling against the uphill wall, which no sealant can hold back for long. In that situation a cricket that removes the ponding usually addresses the cause rather than the symptom. It has to be confirmed on the roof first.
Will a cricket also stop debris from collecting behind my chimney?
Largely, yes. Because the peak splits and steers everything moving downhill around the chimney, needles, grit, and debris are carried past instead of damming at the back wall. That also reduces the moisture those debris piles hold against the masonry.