Flashing comes in many shapes and sizes. There are roof, chimney, window, siding, vent pipe and many other flashings. While most are metal it is possible for a flashing to be some other, waterproof, material.
The basic premise of a flashing is to collect water from above and route it out and away from the house onto the next surface below. It is possible to have many different flashings that water runs across between the top of a house and the point where it eventually falls off. As long as flashings are all installed properly there is no way for harmful amounts of water to get into a house.
Understanding how flashings work and are installed can be a very complex matter. A good analogy that makes the concept easy to understand is that an improperly or poorly installed flashing is the equivalent of tucking your raincoat inside your pants. You’ll quickly discover that you are “flashed” incorrectly.
A very common mistake is to omit flashing and use a liquid sealant product or “caulk”. Caulking will often keep water out of a building for a period of time but will almost always crack, split, deteriorate and leak and some point. Properly installed metal flashings will outlast virtually every other exterior covering or siding type which is the reason they are used.
While it would be nearby impossible to list every flashing that may be found in a house, the following is a list of the more common ones you are likely to find:
Z-Metal Flashing: This is typically installed horizontally at the transition between two siding materials, above deck ledger boards, or over trim boards that are installed above windows. The purpose is to provide a metal “transition” between the two materials to keep water out.
Drip Edge Flashing: This is installed between the edge of the roof and the back/upper edge of the gutter. The purpose is to bridge the gap between the roof and gutter and ensure that all storm runoff is routed off of the roof and into the gutter.
Rake Flashing: This is installed along the sloped edge of a roof. Similar to all other flashings, the upper edge goes beneath the material above (in this case the shingles) and on top of the material below (in this case the barge rafter or trim board).
Pipe Vent Flashing: These can be found around plumbing vents pipes, furnace vent pipes or metal fireplace flues. When these pipes are cut through the roof there must be some way to seal the gap between the pipe and the roof. The flashing is placed on the roof deck and the roofing materials are wrapped around it in a manner to keep the rain water coming down the roof out of the hole that the pipe makes in the roof.
Step Flashing: This is most often metal 6″ X 6″ squares that are bent at a 90 degree angle and placed at the siding to roof seams around the house. The upper edge is installed under the siding and the lower edge is placed on top of roof surface below. In most cases, there is one flashing installed for each row or “course” of roofing materials.
Kick-out Flashing: This is actually part of the step flashing described above. When a siding to roof seam terminates into a gutter certain steps must be made to ensure the water is routed away from the house and into the gutters. A kick-out flashing consists of a piece of step flashing that is bent at the bottom edge and diverts water out away from the house and into the gutter.
Chimney Counter-Flashing: This actually consists of two separate flashing systems that work together to keep water from seeping into the seam between a chimney and a roof. The first part consists of step flashing pieces that are placed under the roofing material and up against the chimney. Next, metal flashing pieces must be set into the mortar joints between the chimney’s bricks and bent over the exposed upward seam left by the step flashing below.