How to Make Chimney Flashing

Chimney flashing is an important part of the structure of the chimney. Chimneys are known to leak, and it’s usually because of the flashing. You can easily spot water damage to your chimney, and the flashing should be replaced as soon as you see the damage. Doing it yourself will save you as much as several hundred dollars. Here’s what you should know.

Know How to Bend Metal

If you don’t have the tools required to bend metal, or have never done metal work before, this part is not going to be a do-it-yourself job. You will need to make straight bends in the sheet metal with a bending brake. If you aren’t experienced in making complicated bends in metal you will want to call a sheet metal fabricating shop with your measurements to do it for you.

Types of Bends Required

You will need several different types of bends in your sheet metal. Here is a list of the most common ones you will encounter.

Front Base Flashing - You will need a sheet of metal at least 12 inches wider than the width of your chimney. This may need to be adjusted once you get it home by bending the angle to match the roof slope.

Pre-Bent Step Flashing - These are commonly referred to as shingle tins. They are 8 by 8 inch pieces that will be stepped together.

Front Cap Flashing, Side Cap Flashing - This is one of the most important types of flashing to install. The cap flashing will prevent water from coming in around the cap. The cap is the most common place where water damage can occur. This is one that will probably need to be made to get it angles correctly.

Back Cap Flashing
- This is the same as the front and side cap flashing.

Finding Your Roof Slope

Before you can start bending any metal you will need to know how to find the slope of your roof. For this you will need a level and a two foot piece of scrap plywood. Cardboard works if it’s a heavy grade and it won’t bend. Write "roof" on the bottom edge. Use you’re level to draw a line that is at least a foot long on the plywood from corner and label this "run." Along the line marked "run" measure another foot section. Use a square to draw a mark from the run line to the edge of the roof line. This line should be labeled "rise." Use this as a template to find the slope of the roof. Once you have the correct dimensions for the slope you can begin to bend and cut the flashing necessary.

Making your own chimney flashing isn’t a job for the faint of heart. It’s difficult, requires special tools and exact measurements, and leaves no room for error. If you don’t think you are able to follow all the measurements and bend the metal correctly then you should choose to not make it yourself and opt to have the flashing pieces fabricated for your roof.