How does flashing protect my roof from potential leaks?

If you go outside and look closely at your roof, you likely will see several different sections of your roof joining one another at angles. These intersecting planes form a V shape and, since the slope is downward, in heavy rain a good deal of water flows along the bottom of the V. This is all by design, since gravity is used to control and direct the water. To keep this water out of the interior of the house, something is needed to act as a waterproof carrier so that water does not flow under the roof shingles and into the interior of the house.

Vent pipe flashingYou will also notice that pipes (vents) protrude from the roof at various points, providing exhausts for plumbing fixtures and heating systems. Sometimes attic fans are installed to vent the summer heat from the attic. These holes in the roof are other obvious places where leaks can occur. If you have one or more fireplaces, the associated chimneys protruding through the roof offer more places for damaging leaks.

As a final example of potential leak sites, you may have one or more skylights installed in your roof. Since the roof had to be cut out for the skylight to be installed, once again you have a possible place for water leakage into the interior of your house.

So, how are these problem areas addressed? This is the purpose of flashing, which is composed typically of thin sheet metal installed underneath the adjoining shingles so as to form a barrier between water and the interior of the house.

The simplest flashing is that used to protect vent pipes. It consists of a piece of sheet metal with a rubber bonnet, as shown. After the vent pipe is installed, the flashing is placed over it and slid down against the roof. As the roofing shingles are installed, they overlap the sheet metal thereby causing the water to flow safely around the vent.

Flashing used in roof valleysFlashing used in the valleys (where the roofing planes intersect) are shaped like a V and once again the roofing shingles are installed over the sheet metal. In cases where one roof plane is steeper than the other so that water flows unevenly, a barrier may be placed along the V to prevent water from being forced under the opposite-side shingles.

step flashingAs a concluding example, consider how a chimney may be protected. Here, a base flashing is installed first, followed by so-called “step flashing” (because each piece steps up the roof) that is installed in grooves cut into the chimney’s mortar and overlapped by the shingles. For added protection, another layer of flashing is added. Notice that the bottom of this layer is not fastened to the step flashing so that seasonal changes that can cause movement is not impeded.

If you notice that your roof is leaking, the first thing your American Roofing and Vinyl Siding professional will do is inspect all the flashing to make sure it is intact. Repairs are relatively simple and inexpensive. Give us a call today, or complete our online estimate-request form for a free estimate on your residential roofing needs.

Let us know about your experience with flashing in the comments below!


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