How to Put Flashing Around a Chimney: A Comprehensive Guide
Putting flashing around a chimney involves a meticulous process of integrating metal pieces to create a waterproof barrier where the chimney meets the roof. It requires careful cutting, shaping, and sealing to prevent water intrusion and protect your home from costly damage. This guide details the proper methods and materials to ensure a long-lasting, weather-resistant seal.
Understanding Chimney Flashing
Chimney flashing is a critical component of your roof’s weatherproofing system. Its primary function is to divert water away from the vulnerable joint where the chimney structure penetrates the roof. Without properly installed flashing, rainwater and snowmelt can seep into your home, leading to leaks, wood rot, mold growth, and structural damage. A chimney that lasts is a chimney that is properly flashed.
Why Chimney Flashing is Essential
Ignoring chimney flashing can have severe consequences. Even seemingly minor leaks can accumulate over time, causing extensive damage behind walls and ceilings. Identifying and addressing flashing issues early can save you thousands of dollars in repairs down the line. Prevention is always cheaper than the cure, especially when dealing with water damage.
Types of Chimney Flashing
Several types of flashing work in concert to provide complete protection:
- Base Flashing: This is the primary layer, installed where the roof meets the sides of the chimney. It’s often L-shaped and integrated with the roofing material.
- Step Flashing: Applied in overlapping pieces up the sides of the chimney, each step flashing is bent to conform to the chimney and tucks under the roofing shingles.
- Counter Flashing: This component covers the step flashing and is embedded into the chimney’s mortar joints. It prevents water from getting behind the step flashing.
- Cricket Flashing: A cricket, a small diversion roof, is installed on the uphill side of a wide chimney to divert water around it. It helps prevent water from pooling behind the chimney and seeping through.
Step-by-Step Installation Guide
This guide assumes you’re working on a standard brick or stone chimney. For other chimney types, consult a professional. Safety should be your top priority. Wear appropriate safety gear, including eye protection, gloves, and a hard hat. If you are uncomfortable working at heights, hire a qualified roofing contractor.
1. Preparation and Assessment
Before you begin, carefully inspect the existing flashing (if any) and the surrounding roofing material. Note any damage, such as rust, cracks, or missing pieces. Remove the old flashing, taking care not to damage the roofing. Clean the chimney and roof surface thoroughly with a wire brush and broom.
2. Installing Base Flashing
The base flashing is usually installed first. It consists of a single piece that covers the lower part of the chimney where it meets the roof. Measure and cut the flashing to size. Apply a generous bead of roofing sealant where the flashing will contact the roof. Slide the flashing up under the first course of shingles and secure it with roofing nails.
3. Installing Step Flashing
Step flashing is the next crucial layer. Cut individual pieces of flashing, typically 6-8 inches wide. For each course of shingles, bend a piece of flashing at a 90-degree angle. Install each piece so that one side rests against the chimney and the other side rests on top of the shingle. Secure the flashing to the chimney with roofing nails or sealant. Overlap each piece of step flashing by at least 2 inches.
4. Installing Counter Flashing
Counter flashing is designed to cover the step flashing and provide an additional layer of protection. Grind out a shallow groove (about 1 inch deep) into the mortar joints of the chimney. Bend the counter flashing to fit snugly over the step flashing. Insert the top edge of the counter flashing into the groove and secure it with mortar. Ensure the mortar completely seals the gap to prevent water intrusion. Overlap the counter flashing pieces by at least 2 inches.
5. Installing Cricket Flashing (If Needed)
If your chimney is wider than 30 inches, a cricket is recommended on the uphill side. Build a small triangular roof structure behind the chimney, using lumber and sheathing. Cover the cricket with roofing felt and then install shingles to match the existing roof. Install flashing around the cricket to divert water around the chimney.
6. Sealing and Finishing
Apply a final bead of roofing sealant along all edges of the flashing, where it meets the chimney and the roof. This will provide an extra layer of protection against water intrusion. Inspect the flashing carefully for any gaps or weak points and seal them accordingly.
Essential Tools and Materials
- Flashing Material: Aluminum, copper, or galvanized steel (choose based on your roof material and budget)
- Roofing Nails: Galvanized or stainless steel
- Roofing Sealant: High-quality, weatherproof sealant
- Mortar: Type S or Type N mortar
- Angle Grinder: With a masonry cutting wheel
- Metal Shears: For cutting flashing
- Hammer: For driving nails
- Tape Measure: For accurate measurements
- Pencil: For marking cuts
- Safety Glasses: Essential eye protection
- Gloves: To protect your hands
- Hard Hat: If working at heights
Frequently Asked Questions (FAQs)
1. What type of flashing material is best for a chimney?
The best flashing material depends on your budget and the type of roofing material you have. Copper offers the best longevity but is the most expensive. Aluminum is a good compromise between cost and durability. Galvanized steel is the least expensive but may rust over time.
2. How do I know if my chimney flashing needs repair or replacement?
Signs of damaged chimney flashing include: leaks in the attic or around the chimney, water stains on ceilings or walls, rust or corrosion on the flashing, missing or damaged pieces of flashing, and cracked or crumbling mortar around the chimney.
3. Can I install chimney flashing myself, or should I hire a professional?
Installing chimney flashing can be a complex and potentially dangerous task, especially if you’re not comfortable working at heights or with power tools. If you’re not confident in your abilities, it’s best to hire a qualified roofing contractor. Improperly installed flashing can lead to serious water damage.
4. How often should I inspect my chimney flashing?
You should inspect your chimney flashing at least once a year, preferably in the fall before winter weather arrives. Regular inspections can help you identify and address minor problems before they become major issues.
5. What is the purpose of a chimney cricket?
A chimney cricket is a small, sloped structure installed on the uphill side of a wide chimney. Its purpose is to divert water around the chimney, preventing it from pooling and potentially leaking into the house.
6. How much does it cost to replace chimney flashing?
The cost of replacing chimney flashing can vary depending on the size and complexity of the chimney, the type of flashing material used, and the labor rates in your area. Expect to pay anywhere from $300 to $2,000 or more for a professional flashing replacement.
7. What are the common mistakes to avoid when installing chimney flashing?
Common mistakes include: using the wrong type of flashing material, not overlapping the flashing pieces properly, using inadequate sealant, not embedding the counter flashing deep enough into the mortar joints, and neglecting to install a chimney cricket when needed. Proper overlap and adequate sealing are critical.
8. Can I use caulk instead of mortar to seal the counter flashing?
While caulk can be used as a temporary fix, it’s not a substitute for mortar. Mortar provides a much stronger and more durable seal that will last for many years. Caulk can dry out and crack over time, allowing water to penetrate.
9. What is the lifespan of chimney flashing?
The lifespan of chimney flashing depends on the material used and the climate. Copper flashing can last for 50 years or more, while aluminum and galvanized steel flashing may last for 20-30 years. Regular maintenance and inspections can help extend the lifespan of your flashing.
10. What is the best way to remove old mortar from the chimney joints?
The best way to remove old mortar is to use an angle grinder with a masonry cutting wheel. Wear safety glasses and a dust mask to protect yourself from debris. Carefully grind out the old mortar, being careful not to damage the bricks or stones. A chisel and hammer can also be used for smaller areas, but they are less efficient.
11. Is it necessary to use flashing tape in addition to metal flashing?
Flashing tape can provide an extra layer of protection against water intrusion, particularly in areas where the flashing is difficult to seal completely. Using flashing tape is recommended for areas with high exposure to moisture.
12. How do I protect my chimney flashing from the elements?
Regularly clean the flashing to remove debris, such as leaves and twigs. Apply a sealant to protect the flashing from corrosion. Consider installing a chimney cap to prevent rainwater from entering the chimney. Preventive maintenance is key to prolonging the life of your chimney flashing.