Chimney Crickets: The Small Roof Part That Prevents Big Leaks

Chimney Academy · How it works · Updated October 2026

What a cricket does

Picture water running down a sloped roof. A chimney is a wall standing in its path. On the downhill side, water flows around the chimney easily. On the uphill side, water hits the wall, stops, and spreads sideways, slowly. Leaves, grit, and snow collect there too. Without a cricket, that uphill corner turns into a shallow basin.

A cricket is a small roof of its own, shaped like a little ridge with two sloping faces that meet at a peak against the chimney. It splits the water into two streams that move to either side of the chimney and rejoin the main roof slope. One building-industry article describes water backing up behind a chimney as one of the most common causes of roof leaks.

The cricket does not replace flashing. It makes the flashing’s job easier by reducing how much water and debris reaches the most vulnerable joint on the whole roof, the uphill corner of the chimney.

When a cricket is expected

Wider chimneys catch more water, so the rule of thumb scales with width. Common building practice calls for a cricket behind any chimney wider than 30 inches, measured parallel to the ridge of the roof, and a masonry trade group gives the same figure. Building codes are adopted locally, so your municipality’s requirement is the one that applies. When in doubt, check with your local code official.

Narrower chimneys are often built without a cricket and manage fine. That does not mean one never helps. A narrow chimney in a location where snow slides or heavy debris collects can still benefit, and a roofer or chimney professional can say whether it is worthwhile on your roof.

The details of your own chimney, including its width, roof pitch and what is already there, determine the answer. A photo alone seldom settles it.

How the cricket and flashing fit together

Flashing is the layered metal that bridges the gap between the chimney and the roof. A typical system has several pieces, each overlapping the one below so water always runs outward over the layer beneath it.

• Base flashing goes down on the roof first, turning up the chimney face. Brick Industry Association guidance describes it extending at least 4 inches along the roof and 4 inches up the chimney.
• Step flashing runs along the sides of the chimney, woven in with each course of shingles.
• Counterflashing is set into the mortar joints or a cut groove and laps down over the base flashing. The Brick Industry Association describes at least 3 inches of lap.
• Cricket flashing covers the surfaces of the cricket and ties into the other pieces at the chimney face.

On a cricket, the metal covering the peak and valleys is critical. A construction-industry article advises against driving fasteners at the peak and in the valleys, because those are exactly where water concentrates. The cricket’s framing is sheathed like the rest of the roof and covered with a waterproof membrane before the metal goes on.

Ordinary caulk is not a substitute. Masonry trade guidance calls sealant used in place of flashing inferior workmanship; sealant helps at vertical edges but should not carry the load.

Slope and construction details

A cricket’s pitch has to be steep enough to shed water and snow. One industry article suggests framing it with a slope of at least one and a half times the roof’s slope. On a roof pitched at 4 in 12, that would be a cricket of about 6 in 12. The pitch must also work with the roofing material, and metal roofs generally need factory-formed cricket pieces with sealed seams.

Other points that matter:

• Centered and symmetrical. A lopsided cricket sends more water to one side.
• Metal appropriate to the roof’s lifespan. There is little sense in a cricket that wears out long before the shingles.
• Chimney metal choices. Copper and stainless steel are commonly recommended flashing materials for masonry contact, while aluminum is generally unsuited to touching fresh mortar.
• Proper integration with roofing. The cricket should connect with the roof’s water barrier, not float on top of it.

These specifics are installer and roofer work, and local code may add its own requirements. They are included here so you can read a proposal and ask good questions, not to be followed at home.

Signs a cricket or its flashing may be failing

You can often notice trouble from the inside or from the ground before anyone gets on the roof.

• A water stain on the ceiling or wall near the chimney, especially after steady rain or snowmelt.
• Staining at the upper edge of the chimney brick, just above the roofline.
• Visible rust or lifted edges on flashing, seen with binoculars from the yard.
• Black streaks or debris piled in a corner behind the chimney.
• Leaks that happen mostly in wind-driven rain, which can point to unsealed edges of the metal.

Any of these may have other causes, such as a damaged crown, cap or roof penetration. For the broader picture of how flashing fails, see chimney flashing repair and roof leaks, and for general leak tracing, why is my chimney leaking.

Because ice and snow collect behind a chimney, winter makes a poor cricket worse. A leak does not confirm any one cause; an inspection traces it.

Adding a cricket, or repairing one

Adding a cricket to an existing chimney is more than a sheet-metal job. The roof near the chimney is opened up, a small frame is built and sheathed, a membrane goes down, and the flashing system is rebuilt around it. Doing it alongside a roof replacement is common, because the roof is already open.

Because the work spans two trades, roofing and masonry, make sure someone is responsible for the whole assembly. Counterflashing is usually set into the chimney, so a roofer who does not work on masonry may not be able to finish it, and a chimney company may or may not do the roofing portion.

If you are unsure what is failing, a chimney inspection examines flashing, crown, mortar and cap together. AM explains its findings and the options before any work begins. If flashing or leak repair is the answer, it falls under chimney repair.

This guide cannot tell you whether your chimney needs a cricket, and it does not give instructions for installing one. It also does not replace the guidance of your roofer or local code official.

Frequently asked questions

Related reading

• Chimney flashing repair and roof leaks
• Why is my chimney leaking
• Roof replacement and your chimney
• Chimney repair