How to Install Sheet Metal Flashing on Your Roof

What You'll Need
Sheet Metal Flashing
Tin Snips
Metal Break Tool
Staple Gun
Roofing Tar

Sheet metal flashing installation is done prior to the installation of shingles. The flashing is used to channel water down to a gutter or directly to the ground. It also plays an important role in keeping water from entering the attic.

Step 1 – Material Preparation

Determine where the flashing will be installed – e.g. roof valleys, around chimneys and vents. Measure the length required, and purchase sufficient materials from a local store. There are different types of metal flashings available. There are those made of lead, copper, and iron. But the best one for the job is aluminum. If the flashings are to be overlapped and require soldering, use galvanized iron, copper, lead or any other material aside from aluminum.

Step 2 – Roof Preparation

Cover the roof with felt paper. If the flashing is to be replaced on a finished roof, remove the shingles covering the flashing and remove it accordingly. There is no need to remove and replace the felt paper. Clean the surfaces carefully and use a portable vacuum to remove any debris that could make the surface of the roof uneven.

Step 3 – Cut and Fold the Flashing Material

Cut the flashing material with tin snips according to the required length. Make the cuts square. For valleys, fold the material lengthwise, using a metal break tool. Create the bend at the middle of the length. Since the material is usually 8 inches in width, the bend should be made to create 2 4-inch sides. For chimneys and vents, be sure that the flashing covers at least 3 inches on all sides.

Step 4 – Install the Flashing

For valleys, position the material in between 2 roofs. The middle portion should be positioned exactly at the joints. Check to make sure that both sides of the bend are flush with the roof, without any errors in the bend angle. For vents and chimneys, ensure that the flashing materials are flush with all sides to ensure they do not leak. Attach the staples to secure it to the roof. The staples should be at least 1 inch from the edge of the material and spaced at least 6 inches from each other. Flashings around vents and chimneys should be stapled both on the inside and outside edges.

Step 5 – Install the Roofing Material

To ensure that the flashings are protected from the effects of external elements, cover them with shingles or roofing tiles. If the installation is done for repairs, re-install the tiles or shingles previously removed. To provide additional protection, apply a coat of roofing tar before installing the roofing materials.


When installing sheet metal flashing for vents, the edges, especially the upper portion of the flashing, should always be covered with shingles to prevent water from leaking into the attic. Remove the shingles around the vent prior to installing the flashing. When the installation is complete, re-place the shingles to conceal the metal from view. Test the area by pouring water around it and check for any sign of leaks underneath the roof.