What Is a Chimney Cricket and Do I Need One?

The problem a cricket solves

On a sloped roof, everything runs downhill until it hits the chimney. On the uphill side, water, wet leaves, pine needles and snow pile up in the flat corner between the roof and the brick. That corner stays wet longer than any other part of the roof, and the flashing there, usually a back pan turned up the chimney, takes the most punishment.

A narrow chimney sheds that water around its sides without much trouble. A wide one acts like a dam. Leaves build into a damp mat, snow drifts against the brick, and in winter ice can build up behind it as snow melts by day and refreezes at night. The water that sits there finds every gap in the flashing and every open mortar joint just above it.

Signs the back of the chimney is the problem

Leaks from the uphill corner have a recognizable pattern. They tend to show on the ceiling or in the attic on the side of the chimney facing up the roof, and they are often worst after heavy snow or during long, steady rain rather than brief storms.

• Stains or rot in the attic on the uphill face of the chimney
• A mat of leaves or debris behind the chimney seen from the ground or a window
• Ice building behind the chimney in winter
• Rust or patching tar on the back pan flashing
• Mortar joints washed out on the back face of the chimney just above the roof

What a cricket looks like

From the side it looks like a tiny roof with its own ridge, sitting behind the chimney and pointing up the slope. It is framed with wood on top of the roof deck, covered with sheathing, then roofed and flashed so it ties into the main roof on both sides and into the back of the chimney. Two small valleys form where it meets the main roof, carrying water down past each side of the chimney.

Some are covered with the same shingles as the rest of the roof. Others are covered entirely in sheet metal, such as copper or coated steel, which is common on steeper roofs, slate roofs or where the cricket is small.

Cricket vs saddle

Most roofers use the two words for the same thing. Some use saddle for a smaller version, or for one made entirely of formed metal, and cricket for a framed one covered in roofing. Either way, the job is the same: give water a slope to run off the back of the chimney instead of a flat corner to sit in.

Whatever the name, size matters. A cricket should span the full width of the chimney and rise high enough that its slope actually carries water away; a token wedge of metal that only covers the middle of the back face leaves wet corners at both ends. On slate and tile roofs, where the main roof is steep and the materials are brittle, the cricket is often fully metal and soldered, and the work is planned around the roofing so pieces are not cracked in the process.

Do you need one?

A chimney that sits on the ridge of the roof has no uphill side, so it needs no cricket. A narrow chimney on a slope may do fine with good step, back pan and counter flashing. A wide chimney partway down a slope is the classic case for a cricket, especially if it has a history of leaking at the back. Many building codes require a cricket on chimneys above a certain width on sloped roofs; the threshold and details are set by the code your town has adopted, so a roofer or building department can confirm it for your house.

Many rowhouses have flat or nearly flat roofs. On those, the issue is ponding water around the chimney base rather than water rushing down a slope. The answer there is usually tapered insulation or roofing that builds a slight slope away from the chimney, plus well-sealed base flashing and counter flashing, not a classic peaked cricket.

• On the ridge: no cricket is needed; step and counter flashing on both slopes do the job
• Narrow and partway down a slope: sometimes; a good back pan may be enough, with a cricket if it keeps leaking
• Wide and partway down a slope: usually; a framed cricket with lined valleys
• Flat or low-slope roof: no peaked cricket; tapered roofing and sealed base flashing instead

Cricket flashing

The flashing is what keeps a cricket dry. Metal runs up the back of the chimney under the counter flashing, the cricket's own roofing laps over the main roof, and the valleys where the cricket meets the main roof are lined so water runs cleanly down both sides. A cricket with poor flashing can leak just like the corner it replaced, and a cricket covered in tar instead of properly flashed is a common source of repeat leaks.

On older chimneys, the counter flashing above the cricket is often surface-mounted and caulked. Setting it into a ground mortar joint makes the whole assembly more durable.

When it is added and what the work involves

The easiest time to add one is when the roof is being replaced or the chimney flashing is being redone, since the area is already open. The old back pan comes off, the cricket is framed and sheathed on the deck, underlayment and roofing go on, the valleys are lined, and new flashing and counter flashing tie everything into the brick.

If your chimney keeps leaking at the back corner, ask whether a cricket belongs there as part of the flashing repair. Also have the crown, cap and mortar above the roof checked, since water entering higher up can run down and appear at the same spot.

What a homeowner can see without climbing

From the yard or an upper window, look behind the chimney for a pile of leaves or a dark, wet patch on the roof. In winter, notice whether ice builds up behind it after snow. Check gutters below that side for granules and debris. Leave the roof itself to someone with fall protection, especially in wet or icy weather.

If you already have a cricket, the same checks apply: debris in its valleys, lifted metal where it meets the brick, and stains in the attic below it after a storm.