How to Install a Chimney Cricket to Prevent Leaks
A chimney cricket is a triangular metal structure installed behind your chimney to divert water away from the base and prevent leaks.
Installing a chimney cricket involves measuring the chimney, cutting flashing material, and securing it with proper sealant and fasteners.
What Is a Chimney Cricket and Why You Need One
Your chimney sits on your roof like a big rock in a stream. Water flows around it, but some gets trapped behind it. That’s where problems start.
A chimney cricket acts like a tiny roof behind your chimney. It slopes water away instead of letting it pool. Think of it as an umbrella that never gets wet but keeps everything else dry.
Signs You Need a Cricket Installation
Water stains on your ceiling near the chimney mean trouble. You might see:
- Dark spots or discoloration on interior walls
- Peeling paint around the fireplace
- Musty smells in rooms near the chimney
- Ice buildup behind the chimney in winter
Don’t wait for major damage. These signs tell you water is already finding its way inside.
Tools and Materials You’ll Need
Essential Tools for the Job
- Measuring tape
- Tin snips or metal cutting shears
- Drill with masonry bits
- Hammer
- Chalk line
- Level
- Safety harness and non-slip shoes
Materials You’ll Purchase
- Sheet metal (aluminum or copper work best)
- Roofing cement or polyurethane sealant
- Masonry screws or roofing nails
- Metal primer and paint (if using aluminum)
I found that copper lasts longer than aluminum but costs more upfront. Many experts say aluminum gives you good value for most homes.
Safety First: Roof Work Precautions
Weather and Timing Considerations
Never attempt this work on wet or windy days. Your roof becomes a skating rink when damp. Pick a calm, dry day with temperatures above 45°F.
Morning hours often work best. The roof stays cooler and less slippery.
Personal Protection Equipment
Wear rubber-soled shoes with good grip. A safety harness isn’t optional – it’s lifesaving equipment. Attach it to a solid anchor point away from your work area.
Keep someone else around while you work. They don’t need to climb up, but having another person nearby adds safety.
Step 1: Measuring Your Chimney
Getting Accurate Dimensions
Measure the width of your chimney at its base. Then measure from the back of the chimney to where you want the cricket to end on the roof.
Most crickets extend 2-3 feet behind the chimney. Going further doesn’t help much. Going shorter leaves you vulnerable to water problems.
Calculating the Slope
Your cricket needs enough slope to shed water quickly. A 1-inch rise for every 12 inches of length works well. So if your cricket extends 24 inches, it should rise 2 inches.
| Cricket Length | Recommended Rise | Slope Angle |
|---|---|---|
| 18 inches | 1.5 inches | 4.8 degrees |
| 24 inches | 2 inches | 4.8 degrees |
| 36 inches | 3 inches | 4.8 degrees |
Step 2: Creating Your Cricket Template
Drawing the Pattern
Use cardboard to make a template first. This saves expensive metal if you make mistakes. Draw a triangle with your measured base width and desired length.
Add 3-4 inches on each side for overlap. These flaps will tuck under your existing shingles.
Testing the Fit
Hold your cardboard template against the chimney. Does it sit flush? Does water have a clear path to flow away? Adjust before cutting metal.
Step 3: Cutting and Shaping the Metal
Transferring Your Pattern
Lay your metal sheet flat. Trace around your cardboard template with a marker. Double-check your measurements before cutting.
Making Clean Cuts
Good tin snips make this job much easier. Cut slowly and follow your lines. Rushed cuts create jagged edges that won’t seal properly.
File any rough edges smooth. Sharp metal edges can cut through sealants and create new leak points.
Forming the Cricket Shape
Bend your metal along the center line to create the triangular shape. The peak should point away from your chimney. Make crisp, clean bends.
Step 4: Installing the Cricket Base
Preparing the Roof Surface
Clean the area behind your chimney. Remove any debris, loose shingles, or old sealant. The metal needs solid contact with the roof.
You might need to lift a few shingles to slide the cricket underneath. Do this gently to avoid tearing the shingles.
Positioning for Proper Drainage
Place the cricket so water flows toward the sides of your chimney, not straight down the roof. This prevents water from backing up under shingles.
The highest point should sit flush against the chimney base. The outer edges should lie flat against the roof.
Step 5: Securing the Cricket
Fastening to the Roof
Drill pilot holes through the metal and into the roof decking. Use masonry screws if you’re hitting concrete or brick. Regular roofing screws work for wood.
Don’t over-tighten. You want the metal snug but not dimpled or warped.
Fastening to the Chimney
The upper edge must attach securely to the chimney itself. Masonry screws work best here. Drill carefully to avoid cracking bricks or mortar.
Step 6: Sealing and Weatherproofing
Choosing the Right Sealant
I researched different sealant types and found polyurethane works better than basic roofing cement. It stays flexible as temperatures change and lasts longer.
Silicone sealants work too, but they’re harder to paint if you want to match your roof color.
Applying Sealant Properly
Clean all surfaces before sealing. Run a continuous bead of sealant where the metal meets the chimney. Don’t leave gaps.
Seal under the side flaps where they meet the roof. Water loves to find these small openings.
Smoothing the Seal
Use your finger or a plastic tool to smooth sealant joints. This creates better adhesion and looks neater. Work quickly before the sealant starts setting up.
Step 7: Final Inspection and Testing
Checking Your Work
Walk around your chimney and look for gaps or loose spots. Wiggle the cricket gently. It should feel solid and immovable.
Pour a bucket of water behind the chimney and watch how it flows. Water should move quickly away without pooling anywhere.
Testing with Weather
The real test comes with the first good rainstorm. Check your interior walls and ceiling for any new water signs after heavy rain.
Common Installation Mistakes to Avoid
Making the Cricket Too Small
A tiny cricket won’t divert enough water. Size it properly for your chimney width and roof slope.
Poor Sealant Application
Rushing the sealing step causes most failures. Take time to clean surfaces and apply sealant thoroughly.
Inadequate Fastening
Wind can lift poorly secured crickets. Use enough fasteners and place them strategically.
Maintenance and Longevity Tips
Regular Inspection Schedule
Check your cricket every spring and fall. Look for loose fasteners, cracked sealant, or metal damage.
Clear any debris that collects around the cricket. Leaves and twigs can block water flow.
When to Call Professionals
Large chimneys or complex roof layouts might need professional help. If your chimney is wider than 30 inches, consider hiring experienced roofers.
Steep roofs also increase difficulty and danger. Your safety is worth more than the money you’d save doing it yourself.
Conclusion
Installing a chimney cricket protects your home from expensive water damage. With proper tools, materials, and careful attention to sealing, you can complete this project in a weekend. The key is taking your time with measurements and weatherproofing. A well-installed cricket will protect your home for decades, making this one of the best investments you can make in your roof system. Remember to prioritize safety throughout the process, and don’t hesitate to call professionals if your situation seems beyond your skill level.
How long does a chimney cricket typically last?
A properly installed copper cricket can last 50+ years, while aluminum crickets typically last 20-30 years with proper maintenance. The sealants may need refreshing every 10-15 years regardless of the metal type.
Can I install a cricket over existing shingles?
Yes, you can install a cricket over existing shingles by carefully lifting them and sliding the cricket flashing underneath. The key is ensuring proper overlap and sealing without damaging the existing roofing material.
What’s the minimum chimney size that needs a cricket?
Chimneys wider than 24 inches typically benefit from crickets, but any chimney that shows signs of water pooling behind it should have one installed regardless of size. Local building codes may have specific requirements.
Do metal crickets need to be painted?
Copper crickets develop a natural patina and don’t require painting. Aluminum crickets benefit from primer and paint to prevent corrosion and match your roof color. Use high-quality metal paint designed for outdoor exposure.
What happens if I don’t install a cricket on a wide chimney?
Water will continue pooling behind the chimney, leading to roof deck rot, interior water damage, ice dam formation, and potential structural problems. The repair costs typically far exceed the cost of installing a cricket preventively.
