With annual rainfall averaging almost 50 inches per year in the Greater Houston Metropolitan Area, how your home sheds water is important to its health and longevity. Our rain often comes as a deluge, pouring thousands of gallons of water on your roof within hours. In torrential rains the water can overshoot full gutters and flow straight down the walls. This is NOT where you want water to go. The water will find its way past the siding and into the wall structure.
Why is this more of a problem now than in the past? Roof structures used to be more simple; even two-story homes tended to have minimal angles and levels of roofing. Currently, homes are being designed with extra levels and angles of roofing to make the home look aesthetically pleasing. Every time the roof changes angle or height, it needs flashing. By keeping water from leaking in these edges, flashing is the most important detail for a roof. There are different types of flashing for use in different areas. But the three types of flashing that can generally be seen after the roof is installed are drip edge flashing, step flashing, and diverter / kickout flashing.
Drip edge flashing is an “L” shaped piece of metal that is installed along the edges of the roof. They direct water away from the roof and into the gutter, if there is one. Without this flashing, water can be driven beneath the shingles where it can penetrate the soffit, which will deteriorate.
Step flashing can be seen at intersections of the roof and a wall. The wall siding should begin 2 inches above the roof shingles. The siding and shingles should never be closer because water will wick up into the siding and deteriorate it. This is the most common failure point of all siding, including cement board. Step flashing is applied beneath the shingles and the siding to assist the movement of water downward into a gutter or over the edge. The separation should be able to be seen.
Diverter or kickout flashing has several common applications. The most important use of diverter flashing is to turn water away from the wall and into the gutter. This prevents gallons of water dumping down the side of the house and entering the wall structure beneath. This is a required detail that is often missed even on new homes. The need for diverter flashing also applies to brick homes and not just other types of siding. Today’s more complicated styles of roofing demand more areas of diverter flashing and it’s easy to miss a few places. This is trouble waiting to happen.
Another shape of diverter flashing fits into the bottom of a valley where two angles come together and is a low point. This flashing slows the water down and forces it to the sides and into the gutters. It is a tremendous help in protecting the ground beneath from being pounded into muddy pools by fast and furious deluges. A final shape of diverter flashing is a simple large “L” shape that is installed at the bottom of the roof above areas for protection of equipment. These are commonly seen above A/C units and improve the cabinet’s ability to protect the equipment.
As a final note: If you are having a roof replaced, make sure the company does not use your old flashing or vent penetrations to save money. Reputable roofing companies wouldn’t allow that because the old flashing does not seal properly and can allow water under the new composition roofing.
While there are several different types of flashing, they all serve the purpose of keeping the storm water shedding from your roof and out of the house where it can deteriorate the structure.