Proper installation of step flashing is important in preventing leaks where a roof meets a wall or other vertical surface like a chimney. This article describes what step flashing is and how it is properly installed.
It is called step flashing because it is made by multiple pieces of flashing that step up the roof with each course of shingles, when it is finished it looks like steps going up the wall.
This article assumes that you are applying a new roof. The dimensions described are for a 12 inch three tab shingle. There are different flashing sizes for different types of shingles. All step flashing is installed where the roof meets the wall so the instructions below assume that you are installing step flashing somewhere along the roof to wall connection.
brief how to
In this article, you will find information about:
The roofing should be installed up past the corner by at least 7 inches before beginning to install step flashing. This is so that the first piece of flashing can go on top of the roofing, this keeps the water on top of the roof.
Start by attaching flashing at the bottom corner of the roof to wall connection. This piece of step flashing will be cut at the bend in the flashing. Cut from the corner that is over the roof at a 45 deg angle down to the bend. Put the uncut sides and bend on the horizontal joint between the roof and the wall. Bend the piece above the cut up the roof and let the piece below the cut lay flat on the roof. Nail the flashing on the top corner of the bent piece and the opposite corner on the horizontal wall.
Nailing should always be done on the wall 1/2 inch from the top of the flashing. This keeps leaks from happening where nails go thru the flashing.
Apply roofing cement from the corner across the flat side of the flashing along the nail line on the shingle. Then apply mastic from the bottom of the corner up the wall on the rake side of the flashing to the top of the flashing. The corner where the rake of the roof meets the wall is probably the most vulnerable spot because there is a hole at the corner that can easily leak if not caulked with roofing mastic properly.
The first step flashing will be installed directly over the corner flashing before a course of roofing is installed. The bottom horizontal and vertical edges will be embeded into the roofing mastic that you applied in the last step. Install a nail on the top corners. Bend the top vertical edge around the corner and nail it to the wall.
Install the next course of roofing over the corner and step flashings. Then install the next step flashing making sure the bottom edge of the flashing is installed just over the nail line on the shingle below it. Repeat this process with each course of roofing.
Flash the top by taking the last piece of flashing and measuring from just below the nail line to where the flashing touches the ridge. Cut down the fold line on the flashing to this point so it can be bent over the ridge and go down the other side of the roof. Put the piece of flashing on as you did the others and then bend the top down at the ridge. You will cover the bend down with the roofing from the other side of the roof.
After installing the roofing and step flashing on the second side of the roof you are ready to install the last piece of top flashing. It is cut just as the top flashing for the first side was and installed with the bend over the ridge. The ridge cap is installed over the top of all this.