Roof flashing
Roof flashing is a thin material, usually galvanized steel, that professional roofers use to direct water away from critical areas of the roof, wherever the plane of the roof meets a vertical surface such as a wall or dormer. Flashing is installed to surround roof features such as vents, chimneys, and skylights. The water should run down the side of the flashing and be directed onto the shingles instead of finding its way onto the roof deck.
Installing a roof plumbing vent is practically an easier task than capping a chimney. This is how to do it:
Step One: Install the shingles as usual to the base of the pipe vent.
Step Two: Place the flashing or cap on the pipe vent so the base rests on the shingles. Momentarily lift the cap and apply sealant to hold the flashing in place.
Step Three: Firmly push the flashing down into place.
Step Four: Install the next row of shingles. When you reach the pipe vent, allow the shingles to overlap the top of the flashing.
Step Five: To make room for the vent itself, cut a circular piece of the shingles, as shown below.
Step Six: To secure the circular edge of the shingle, apply roofing cement underneath it. Also be sure to nail it where you normally would.
Types of Roof Flashing
There are almost as many types of flashing as there are parts of the roof! After all, every roof feature needs protection. Here are the important types of roof flashing you need to understand:
Continuous Flashing: Continuous flashing is also called “apron flashing” because it looks a lot like an apron. It is a single, long piece of metal that carries water down to the shingles below. Long pieces of continuous flashing will have trouble flexing as the house expands and contracts in the changing seasons. If left as is, it could break or warp and not let water in. Therefore, long pieces have built-in expansion joints so they can move with the house.
Base Flashing: Some roof features, such as chimneys, require two pieces of flashing. This ensures that rain always meets an intermittent surface that directs it downward. Additionally, it is notoriously difficult to install flashing around a chimney. Two-part flashing has another advantage: When roofing materials naturally expand and contract with weather changes, the two pieces can move, so the entire system remains secure. The flashing base (or apron) is the bottom piece.
Top flashing: Placed in front of the flashing base, or on top of the flashing base, the top flashing completes the two-part kit.
Step siding: Step siding is a rectangular piece of flashing bent 90 degrees in the center. It is used as roof-to-wall flashing. Multiple pieces of flashing will be installed in layers with shingles to ensure water flows away from the wall.
