Look at the uphill side of a wide chimney on a well-built roof and you will usually see a small peaked structure tucked against the brick, like a miniature roof. That is a chimney cricket, also called a saddle. Its job is simple: split the water running down the roof and steer it around the chimney instead of letting it pile up against the masonry. When a wide chimney does not have one, or when the one it has is poorly built or flashed, the back of the chimney becomes one of the most leak-prone spots on the house.
This guide explains what a cricket does, when building rules and good practice call for one, how a roofer frames and flashes it, the choice between metal and shingled crickets, and the leak points we check before the autumn rains and the first snow.
What A Chimney Cricket Does
A chimney that rises through a sloped roof acts like a dam. Everything coming down the roof above it, rain, meltwater, leaves, needles and snow, runs straight into its uphill face. On a narrow chimney, water simply flows around the sides. On a wider chimney, the flat area behind the brick becomes a pocket where water slows down, debris collects and snow drifts in against the masonry.
A chimney cricket replaces that flat pocket with two small sloped planes that meet at a ridge in line with the centre of the chimney. Water hitting the cricket is diverted to each side, where it continues down the roof past the step flashing. The benefits:
- No standing water behind the chimney, so the flashing is not submerged during heavy rain.
- Less debris build-up, which otherwise holds moisture against the shingles and brick.
- Less snow and ice packing in the corner, reducing freeze-thaw stress on the flashing and mortar.
- Longer life for the masonry, because the back face of the chimney stays drier.
Most chimney leaks we see are at the flashing, and a missing or failing cricket makes the back flashing work much harder. If the brick, crown or mortar are also worn, a cricket is best built or rebuilt alongside chimney repairs and reflashing.
When A Chimney Needs A Cricket
Whether a chimney cricket is needed depends mainly on how wide the chimney is across the slope, with roof pitch and site conditions as secondary factors.
What the building rules say, in general terms
Ontario’s building rules for houses call for a chimney saddle where the upslope side of a chimney on a sloped roof is wider than a set limit, commonly cited as about 750 mm (roughly 30 inches). North American model codes use a similar threshold. The measurement is the chimney’s width perpendicular to the slope, across the uphill face. Rules also cover how the saddle is flashed and the materials used. Treat this as a general explanation; confirm current requirements with your municipality, especially if a permit applies to your project.
When good practice goes further
Experienced roofers often recommend a cricket even on chimneys narrower than the threshold when:
- The roof pitch is low, so water moves slowly and can back up behind the chimney.
- The chimney sits low on a long roof slope, collecting a lot of runoff from above.
- Trees overhang the roof, dropping leaves and needles that pile up behind the chimney.
- Snow drifts against the uphill face every winter.
- There is a history of leaks at the back of the chimney that reflashing alone did not solve.
| Chimney and roof situation | Cricket recommendation | Why |
|---|---|---|
| Wide chimney above the code threshold | Required under the building rules | Large flat pocket collects water and snow |
| Narrow chimney, steep roof, open site | Usually not necessary; a well-built back flashing (backpan) is often enough | Water sheds quickly around the sides |
| Narrow chimney, low pitch | Often recommended | Slow runoff can pond behind the chimney |
| Chimney low on a long slope | Often recommended | High volume of water from above |
| Heavy tree cover above the chimney | Often recommended | Leaves and needles build up at the back |
| Recurring leaks at the back of the chimney | Strongly recommended during repair | Diverting water addresses the root cause |
How A Chimney Cricket Is Framed
A cricket is built on the roof deck, on the uphill side of the chimney, before the underlayment and shingles go on. Roofers usually build or rebuild one during a reroof, or during a chimney reflashing when the shingles around the chimney are already removed.
Laying it out
The cricket is essentially a small gable roof. Its base spans the full width of the chimney’s uphill face. Its ridge runs from the centre of that face back up the roof until it meets the main roof plane. The height of the cricket at the chimney determines its slope, and roofers often aim for a slope that sheds water well without looking awkward. The two sides of the cricket form small valleys where they meet the main roof.
Building the frame
There are two common approaches:
- Stick framing. A ridge board and small rafters or blocking are cut and fastened on top of the roof deck, then sheathed with plywood or OSB. This suits larger crickets.
- Sheathing-only construction. For small crickets, triangular plywood pieces are cut and supported on a centre piece or blocking, forming the two planes directly.
Either way, the structure must be solid enough to be walked on by roofers during work and to carry snow load, fastened securely to the roof framing and cut neatly where it meets the brick.
Flashing A Chimney Cricket
The frame only diverts water if the waterproofing and flashing around it are done correctly. This is where most of the skill lies.
- Self-adhered membrane. The whole cricket, the valleys where it meets the roof, and the lower part of the chimney face are covered with ice and water membrane, turned up the brick several inches. Corners get extra patches.
- Cricket covering. The cricket is covered with either a formed metal pan or shingles over the membrane (see the comparison below).
- Valleys. The small valleys where the cricket meets the main roof are treated like any roof valley, with metal or a well-lapped shingle valley over membrane.
- Step flashing. Along the sides of the chimney, individual step flashings are woven with each shingle course, turning up the brick.
- Front apron. On the downhill face, a continuous apron flashing laps over the shingles below.
- Counter flashing. Metal counter flashing is cut into the mortar joints of the chimney (a reglet) and folded down over the step flashing and cricket flashing, so water on the brick cannot run behind them. Counter flashing should be let into the masonry, not just glued to the brick face with sealant.
The corners where the cricket ridge meets the chimney and where the cricket valleys meet the side step flashing are the most complex points. A good roofer pre-forms metal pieces or uses carefully folded flashing and membrane patches at these corners, rather than relying on sealant.
Metal Versus Shingled Crickets
A cricket can be finished in metal or in shingles. Both can work well; the choice depends on the size, slope and the look you want.
| Factor | Metal cricket | Shingled cricket |
|---|---|---|
| Water shedding | Excellent; smooth surface and few seams | Good if the slope is adequate |
| Best for | Small or low-slope crickets, complex corners | Larger crickets with enough slope for shingles |
| Appearance | Visible metal, can be pre-finished to suit the roof | Blends in with the rest of the roof |
| Durability | Long-lasting when material and gauge are suitable | Similar to the surrounding shingles |
| Installation | Requires sheet metal fabrication skills | Standard shingling, with careful valleys |
| Debris | Sheds leaves and needles more readily | Granular surface can hold more debris |
| Snow and ice | Snow slides off more readily | Holds snow longer |
Shingles have a minimum slope below which the manufacturer does not permit them. Many small crickets end up too shallow for shingles, which is one reason metal is common on smaller installations. Metal crickets are usually fabricated from galvanized or pre-finished steel, aluminum or copper, and they are formed to fit the specific chimney.
Common Leak Points Before Autumn Rain And Snow
Even a cricket can leak if its flashing is poorly detailed or has aged. Here are the problems we find most often, and the interior signs that tend to go with them.
| Leak point | Typical cause | Indoor sign |
|---|---|---|
| Corner where cricket ridge meets brick | Poorly folded flashing, sealant used instead of metal | Ceiling stains near the chimney breast or damp wood seen from the attic hatch |
| Cricket valleys | Debris build-up, shingles cut incorrectly, no membrane | Damp sheathing beside the chimney |
| Counter flashing | Face-sealed rather than let into mortar, deteriorated mortar joints | Water running down the chimney inside the attic |
| Masonry above the flashing | Cracked crown, porous brick or failed mortar letting water in from above | Stains on the chimney breast or walls beside the fireplace |
| No cricket on a wide chimney | Water and snow ponding at the back | Recurring leaks during heavy rain and thaws |
| Rusted or holed metal | Old, low-grade or unpainted metal pans | Drips that start after years without problems |
Some chimney leaks are not coming from the roof flashing at all. Water can enter through a cracked crown, porous brick or deteriorated mortar joints higher up and run down inside the chimney. A roofer considers the whole chimney, not just the flashing, when diagnosing. That is why the flashing and masonry are often assessed and repaired together.
Why Autumn Is The Time To Check
A chimney without a cricket, or with a worn one, tends to reveal itself in two seasons: heavy autumn rain and the first freeze-thaw cycles. Leaves also fall right when rainfall picks up, filling the back of the chimney with wet debris.
Building or rebuilding a cricket is best done in mild weather. Membranes bond well on a warm, dry deck, shingles are pliable enough to lift and reseal, and mortar used to set counter flashing cures better above freezing. Leaving the work until winter usually means a temporary patch and a proper repair in spring.
Homeowners should not go onto the roof to look behind the chimney. The signs worth noticing from inside are stains on the ceiling or walls near the chimney breast, damp or discoloured wood around the chimney seen from the attic hatch, or a musty smell near the fireplace. Any of these are reasons to book a professional inspection.
Adding A Cricket To An Existing Roof
A chimney cricket can be added without replacing the whole roof. The roofer removes the shingles and flashing around the chimney, frames the cricket on the deck, installs membrane and new flashing, then reshingles the area and blends the new shingles into the old. It is typically done alongside chimney reflashing. As a rough guide, adding a cricket with new flashing often falls in the range of several hundred to a couple of thousand dollars or more, depending on the chimney size, roof pitch, access, the metal chosen and whether masonry work is needed. That is an estimate only; every chimney is different.
If your roof is near the end of its life, it is more economical to build the cricket during a full roof replacement, when all the surrounding shingles are coming off anyway.
Questions To Ask Your Roofer
- How wide is my chimney across the slope, and does it need a chimney cricket under the building rules?
- If it is narrower, would a cricket still help on my roof?
- Will the cricket be metal or shingled, and why?
- Will the counter flashing be cut into the mortar joints?
- Is the chimney masonry, crown and mortar in good enough condition, or does it need work at the same time?
- Will the underlayment around the chimney be replaced with self-adhered membrane?
You can find more answers on our FAQ page.
What is a chimney cricket?
When is a cricket required?
Can a chimney cricket be added to an existing roof?
Is a metal or shingled cricket better?
Why is my chimney still leaking after reflashing?
Can I check the back of my chimney myself?
Protect Your Chimney With A Properly Built Chimney Cricket
A well-framed and flashed cricket keeps water moving around your chimney through the autumn rain and the winter ahead. At The Roof Technician, we assess chimney width, flashing and masonry, and build crickets that are detailed to last.
Call us today at (416) 826-0040 or request a free estimate.
Serving homeowners across Toronto and the GTA.