Lead flashing plays a very important role in keeping your roof waterproof and durable. It is a thin sheet of lead used to cover joints and edges on roofs, preventing rainwater from seeping inside. If installed properly, lead flashing can last for decades and protect your home from leaks and water damage. We’ll discuss how to install lead flashing step by step in simple and easy English so anyone can understand the process clearly
What is Lead Flashing?
Before starting the installation, it’s important to understand what lead flashing actually does. Lead flashing is usually placed around chimneys, valleys, dormer windows, roof joints, and walls. It creates a tight seal between different parts of the roof, ensuring that rainwater flows away smoothly. Because lead is flexible and durable, it can be shaped easily and withstands different weather conditions.
Lead flashing also expands and contracts naturally with temperature changes, which helps it stay in place for many years. This is why professional roofers often choose lead over other materials.
Tools and Materials You’ll Need
To install lead flashing properly, you’ll need a few basic tools and materials:
- Lead flashing rolls (choose the right thickness for your roof)
- Lead dressing tools or a lead bossing stick
- Masonry chisel and hammer
- Lead wedges or fixing clips
- Sealant or mortar mix
- Tape measure and pencil
- Safety gloves and goggles
- Ladder or scaffolding
Having the right tools ensures the job is safe, neat, and long-lasting.
1. Prepare the Area
Before you begin, make sure the working area is clean and safe. Remove any dirt, moss, or old flashing from the area where you’ll be working. Check for damaged mortar or cracks in the wall or chimney and repair them first.
It’s also important to check the weather. Always install lead flashing on a dry day to ensure the sealant and mortar set properly. Wet conditions can make the job dangerous and less effective.
2. Measure and Cut the Lead Flashing
Measure the area where the flashing will be installed. Use a tape measure to get accurate measurements for both length and width. Add a few extra centimeters to allow for overlaps and bends.
Once measured, mark the lead sheet with a pencil and cut it carefully using a sharp utility knife or tin snips. It’s better to cut several shorter pieces rather than one long strip, as shorter sections are easier to handle and shape.
Remember, lead flashing comes in different codes or thicknesses. For most domestic roofs, Code 4 or Code 5 lead flashing is commonly used.
3. Shape the Lead Flashing
Now it’s time to shape the lead to fit the surface. Lead is soft and flexible, so it can be bent or curved using a lead dresser or bossing stick.
If you are installing flashing around a chimney, you’ll need to create a step pattern known as “step flashing.” This involves cutting the lead into small rectangular pieces that overlap each other like stairs. Each step should be about 150 mm wide with an overlap of at least 100 mm to ensure proper waterproofing.
Take your time with this step—accurate shaping makes your work look professional and ensures the flashing fits tightly.
4. Cut the Chase in the Wall
To fix the lead flashing securely, you need to cut a groove (called a chase) into the mortar joint of the wall or chimney. This groove is usually about 25 mm deep and will hold the top edge of the lead.
Use a masonry chisel and hammer to make the chase carefully along the line where the flashing will sit. Once done, brush away any dust or debris to ensure a clean surface for sealing later.
5. Fit the Lead Flashing
Insert the top edge of the lead flashing into the chase. Make sure it fits tightly and sits flat against the wall or roof surface. Use lead wedges or fixing clips to hold it in place. These clips will prevent the flashing from slipping or moving over time.
Press the lead gently into the surface using a lead dresser to make it smooth and neat. Ensure there are no air gaps or loose edges where water can enter.
6. Seal the Chase
Once the flashing is securely in place, the chase needs to be sealed to make it watertight. You can use either a lead sealant or a mortar mix for this purpose. Lead sealant is flexible and long-lasting, making it a better option for most modern roofs.
Fill the chase carefully with sealant using a pointing gun, making sure it covers all gaps completely. Smooth out the sealant for a neat finish. Allow it to dry properly before testing or painting.
7. Dress the Lead Flashing
Now, gently dress the lead down over the roof surface using your lead dresser. This step ensures the flashing sits flush with the tiles or slates and directs water away efficiently.
Avoid hammering too hard, as lead can stretch or tear if excessive pressure is applied. The finished surface should look smooth, with no sharp bends or wrinkles.
8. Check and Final Touches
Once everything is in place, inspect your work carefully. Check all joints, overlaps, and sealed areas to ensure there are no gaps. Pour a small amount of water over the flashing to test if it drains properly.
If you find any loose parts, fix them immediately using extra clips or sealant. Also, clean off any dust or marks for a professional-looking finish.
Maintenance Tips for Lead Flashing
Proper maintenance will help your lead flashing last for decades. Here are a few simple tips:
- Regular inspection: Check your flashing at least twice a year, especially after storms or heavy rain.
- Clean debris: Remove leaves, moss, and dirt regularly to prevent water buildup.
- Re-seal if needed: If you notice cracks or gaps in the sealant, reapply fresh sealant immediately.
- Avoid paint or coatings: Lead naturally forms a protective layer, so avoid painting over it unless it’s a specific protective product recommended by professional
Common Mistakes to Avoid
Even small mistakes during installation can lead to leaks. Here are some common errors to watch out for:
- Not inserting the lead deep enough into the chase.
- Using overly long strips that cause the lead to sag.
- Not allowing overlaps between pieces.
- Applying sealant on wet surfaces.
- Using nails directly through the lead (this causes cracks later).
Avoiding these errors ensures your flashing remains strong and waterproof for years to come.
Why Choose Lead Flashing Over Alternatives
Some modern roofers use plastic or aluminum flashing because they are cheaper and lighter. However, lead remains the most durable and effective material. It lasts much longer, can be repaired easily, and provides a more traditional and neat finish.
Lead flashing is also eco-friendly because it’s 100% recyclable. Although the initial cost might be higher, it saves money in the long run due to its longevity and low maintenance.
Conclusion
Installing lead flashing like a roofing expert requires patience, precision, and the right tools. When done correctly, it protects your home from leaks, improves durability, and adds value to your property. Whether you’re working on a chimney, roof valley, or wall joint, following these steps carefully ensures professional and lasting results.
Lead flashing is not just a roofing accessory—it’s an essential shield that keeps your home safe and dry through every season. By learning how to install lead flashing the right way, you can ensure your roof remains strong and leak-free for many years to come.