What Is a Chimney Cricket Flashing and Why Is It Necessary?

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A chimney cricket flashing or roof cricket is a type of flashing located at the back of the chimney top. It directs rainwater away from the chimney, preventing water from entering and causing damage. Without a cricket, water can seep into your chimney and damage your chimney masonry and mortar.

Even though homeowners know the importance of a chimney roof flashing, they usually don’t consider it as important. This is a huge mistake as it can cost a lot in repairs.

By installing a chimney cricket you can prolong your chimney’s life. You also save yourself from paying thousands of dollars to fix the damage caused by leaking rainwater.

What Is the Purpose of a Chimney Cricket and Is It Necessary?

A chimney cricket protects your chimney from water leaks.

When it rains, rainwater from your roof flows downward. Some of this water hits the back of your chimney top and starts to collect. The pooling water eats away at the exterior chimney masonry and creates cracks inside the mortar. This causes water to leak inside your chimney, which can be catastrophic for your chimney and its parts.

To prevent water pooling, a chimney expert will install a chimney cricket. This will allow the water to flow away from the chimney and down into the gutter. This is done by building a triangular wooden structure. The structure is then covered by a metal flashing to perfectly seal the spot and prevent water from getting inside.

If you don’t want your chimney masonry to rot away, get a chimney cricket installed by a professional chimney expert.


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When Is a Chimney Cricket Required?

If water settles at the back of your chimney top or you’re facing chimney leaks, you may need a chimney cricket installed. The best way to know is by calling a certified chimney expert for a leak test.

He will spray water on your chimney using a hose and inspect your chimney, attic, and walls near your chimney for any signs of leakage.

If there is a problem, the chimney expert will recommend a cricket flashing of a certain size (according to your chimney top and roof dimensions) and provide a quote for the installation.

Chimney Cricket Code Requirements

While most building codes don’t require homeowners to install a chimney cricket, some consider it mandatory. For example, the Colorado Residential Code demands homeowners to install a chimney cricket if the width of the chimney top (parallel to the ridgeline) is more than 30″.

The code also states that the space between your chimney and the cricket should have flashing and counter flashing like the one installed in areas where the roof meets the chimney.

But if your chimney intersects the ridgeline, you do not need a chimney cricket. That’s because the chimney top in this case is above the roof, so rainwater will not collect by its walls.

How Tall Should a Chimney Cricket Be?

The steeper the chimney slope, the higher the chimney cricket needs to be. For example, if your roof has a 12-12 slope, your chimney cricket should have a height equal to ½ of the width of the chimney top. For a roof with a 6-12 slope, the height should be ¼ of the width of the chimney top.

Similarly, the height of the cricket will reduce with the reducing slope.

Chimney Saddle Flashing vs Chimney Flashing

A chimney cricket is also known as a chimney saddle. It is installed at the back of your chimney and used as a diverter to prevent water from rotting the backside of your chimney masonry.

On the other hand, a chimney flashing is installed at the points where the chimney intersects the roof. Since these parts of the roof are exposed, water can seep inside. That is why a metal flashing is installed to cover the exposed areas.

Both saddle flashing and chimney flashing play an important role in preventing chimney leaks.

Chimney Cricket flashing Installation Guide

Disclaimer: You should always get a certified chimney expert to install a chimney cricket or any other type of flashing. These professionals are equipped with the right tools. They have years of experience that help them get the job done safely, accurately, and without damaging any part of your roof or chimney.

We do not recommend homeowners do a DIY installation of their chimney cricket flashing. That’s because most of them don’t know the best practices, precautionary measures, or the building codes of their locality.

The following step-by-step guide helps homeowners know what to expect from a chimney expert:

Step 1: Calculate Chimney Cricket Dimensions

First, we have to calculate the slope of the roof:

  • Place one end of a ruler on the ridgeline of the roof. Make sure it is parallel to the ground using a level. If the bubble in the level is right in the middle, that means it is parallel to the ground.
  • Use a measuring tape to measure the distance between the ruler at a 12″ mark and the roof.
  • This will give you the slope of the roof.
  • If the distance was 4″, the slope will be 4/12.
  • For a 4/12 chimney, the height of the cricket should be ⅙ of the width of the chimney top according to the IRC code.
  • Mark the calculated height of the cricket onto the back of the chimney top.
  • Use a level and place one end of it on the mark and the other end on the roof (make sure the bubble is at the center.) Drive a nail into the roof at the point of the level.

Step 2: Remove Old Flashing

  • Use a pry bar to remove old flashing from the back of the chimney. Also, remove the shingles in a square from the chimney back to where the nail is placed. Remove all of it until only the chimney masonry and roof decking are left.
  • Waterproof the roof and the sides of the chimney where it meets the roof.
  • Install L-shaped metal flashings at the intersection of the chimney and the roof. Make sure that one part of the flashing covers the roof while the other goes up the sides of the chimney masonry.

Step 3: Construct Beam of Cricket

  • Take a 2″ by 4″ board and cut it at 2 ft.
  • Now we need to cut a slope similar to the roof slope into the board. This can be done for a 4/12 roof slope by measuring 4″ from one end of the board. Now draw a diagonal from that point to the outer edge across the 2″ by 4″ board. Cut the board along that line to create the slope.
  • Place the uncut end of the 2″ by 4″ board against the chimney back such that the slope is flat against the roof.
  • Screw the board into the roof framing using 3″ decking screws.
  • Now we have the main support beam for the cricket in place.

Step 4: Construct Rafters

  • Install two rafters that run along the back edge of your chimney between the roof and the main beam.
  • To construct the rafters, cut out the 2″ by 4″ board from the bottom edge in the same way we did for the main beam. But this time, we’ll measure the slope from the top edge of the main beam at the point where it touches the chimney’s backside.
  • When done, the beam and rafter assembly should make a ‘T’ from the top view.

Step 5: Create Plywood Triangles

  • Take a ½ ″ plywood or oriented-strand board (OSB) and cut out two pieces. Make sure they fit the triangles marked by chalk on both sides of the beam. Using a cardboard dummy first is better to make sure your measurements cover the area perfectly.
  • Make 45-degree beveled edges on the plywoods where they meet over the beam and touch the roof.
  • Fix the plywood with galvanized nails at the rafters, roof, and main beam.

Step 6: Install Protective Covering and Flashing

  • Cover the sides and edges of the newly installed cricket with a waterproof covering to protect it against rain and snow. You can use a construction stapler for the job.
  • Now install metal flashing along the sides of the cricket. Make sure the seams overlap the roof.
  • Also, cover the bent sides with metal flashing through the chimney.
  • Install an L-shaped metal flashing with one side covering the chimney while the other covers the base flashing. This is the counterflashing.

Step 7: Add Shingles

  • Use roofing nails to install shingles over the cricket and roof. Place the shingles such that the bottom half of the successive row covers the top half of the row before it. This prevents leakage.


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How Much Does It Cost to Add a Roof Cricket to a Chimney?

Installing a roof cricket can cost around $2000 to $5000. Various factors come into play when estimating the cost of a chimney cricket flashing installation. The size of the chimney directly affects the size of the cricket required and increases the cost.

Other factors include:

  • Living costs of your area
  • Roofing materials
  • Labor cost
  • Ease of accessibility
  • Condition of your chimney masonry

A chimney damaged because of water collecting at the back of the chimney top needs to be repaired or rebuilt. This will add to the total cost of the installation.

The cost of installing a chimney cricket flashing is high, but you’ll be saving yourself from chimney damage that will cost you exponentially more to repair.

And never try to do a DIY installation of your chimney cricket. You may end up damaging your chimney or rooftop. It’s also possible that the cricket was not installed properly, aggravating the problem of chimney leakage.

The Takeaway

Chimney cricket flashing is like a miniature roof installed at the back side of your chimney top. Its purpose is to divert rainwater from your rooftop and prevent it from pooling against the backside of your chimney.

With a chimney cricket installed you can prevent water damage to your chimney masonry and nearby walls. So if you don’t have a chimney cricket, get a certified chimney sweep to get it installed.

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Thomas Green

Thomas has worked in the Chimney & Fireplace field for over 12 years. He is an expert in his trade and loves to help People with their needs. Thomas Write helpful articles so that homeowners can make the most informed decisions about their fireplace and chimney.