What Is Roof Flashing?

August 5, 2021

What Is Roof Flashing And What Does It Do?

And Why Is It So Important?

If your neighbor tells you your roofer is doing some flashing up there, don’t dial 911. He’s just doing his job, promise. Roof flashing is an essential part of resurfacing a roof system. It keeps rainwater where it belongs, in your gutters, instead of sneaking under your shingles.

Anatomy Of Roof Flashing

Flashing comes in many forms, but they all have the same job: joining a vertical surface with the mostly horizontal surface of your roof while protecting against leaks at the seams. Examples of areas where this is needed are:

  • Chimneys
  • Vent Stacks
  • Solar Arrays
  • Dormers
  • Intersecting Walls

Virtually anything that sticks out of or abuts the shingled surface of your roof needs flashing. Other areas that need flashing include roof edges and gutter systems though that flashing material is called kick-out flashing. Your local building code specifies every instance that needs flashing installed, which all professional roofers are only too happy to follow.

Flashing Materials

Most building codes demand that flashing be made of galvanized steel due to its disability and resistance to corrosion. You will occasionally see flashing made of aluminum, but it must be coated and should never be placed against masonry or an unalike metal to guard against corrosive chemical reactions. Copper is a popular flashing material on high-end projects for its beauty and durability.

Flashing can be purchased pre-made, but most roofing contractors prefer to shape it on the site since you can never tell what odd shape you might encounter. Even when they purchase purpose-made flashing, there’s a more than even chance that they will have to customize it to fit properly. And when it comes to flashing, fit is everything.

Flashing Types

Roof flashing comes in several types, though it may be better to say that flashing is installed using several methods. Each method is designed to counter innate difficulties in waterproofing certain areas.

Continuous Flashing

Also known as Apron Flashing, this method uses long flashing pieces that hang like an apron from a vertical surface and down to the shingles. To keep this flashing from warping out of shape, expansion joints are placed in the apron to allow for flexing and movement in the roof.

Base Flashing

One of two pieces of flashing most often used for chimneys, base flashing is the bottom piece set around the chimney base and directly against the roof surface.

Counter Flashing

Counter flashing covers the vertical portion of the chimney and drapes down to the base flashing. This two-piece system is simpler than trying to force a single piece of flashing to do the job and also allows for expansion and contraction without losing its effectiveness against moisture.

Step Flashing

Step flashing is a series of rectangular panels set where a vertical feature meets the horizontal lines of the roof. They are set, one after the other, in a stepped fashion, to protect the seam where the two opposing areas of the home meet.

Cap Flashing

Cap flashing has a cylinder up the center that slips tightly over round roof vents. The cylinder opens to an apron that sits above the shingles and directs rainwater away from the vent opening in the roof.

Flashing Mistakes To Watch For

Installing flashing properly takes expertise and patience. Unfortunately, it is very easy to mess up a flashing installation. While mistakes can happen, there are a few items to watch out for that are simply poor performance.

Not Following The Mortar Lines

If you put flashing on a vertical surface with mortar lines, you must shape the top of the flashing to those lines. Then, you need to create 90-degree folds on the top edge. Those folds will create a direct line of contact between the flashing and the mortar, which allows for a nice, watertight seal when you place the sealant.

Some roofing contractors will just fill the mortar lines with sealant and leave the flashing flat across the mortar gap. While this will hold for a little while, it won’t hold up for the decade or more you expect from a new roof.

Skipping Edge Flashing

Not every building code demands edge of kick-out flashing in every situation, but any reputable roofing contractor will install it anyway. Edge flashing makes sure that the water is well beyond the roofing before gravity takes hold of it, which keeps the water from seeping back up under the shingles.

Using The Wrong Materials

While it is perfectly fine to manufacture flashing on-site, the flashing needs to be made of the right materials. Galvanized steel and copper are your best bets. However, the sealant used is almost more important than the metal. Roofing cement is best for securing and sealing flashing. Using standard caulk is a big no-no.

What Happens If Flashing Fails?

The quality of your flashing can make or break the lifespan of your roof. Flashing failures can cause a tremendous amount of damage before you notice you have a problem.

Flashing leaks are often quite small, which means they can be there for months before you notice watermarks in your home. However, you could have developed rotten planking, weakened joists, and insect or mold activity from the constant moisture in that area during that time.

How Do You Protect Yourself?

Since flashing leaks can take months to show themselves, you only have a couple of ways to protect yourself. The first is to get your roof inspected once a year and after any major storm. The sooner you find a problem, the less expensive the roof repair will be.

The second way is to use a roofing contractor who has been around for at least a decade and has a great online reputation. Most roofing companies fold within the first five years, so finding an established company is best. That way, if there is a problem down the line, you can feel confident that they’ll still be around when you call.

If you are concerned about the quality of work on your Houston area roof, contact us at Houston Roofing for a free inspection.

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