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 roof plane meets a vertical surface like a wall or a dormer. Flashing is installed to surround roof features, such as vents, chimneys and skylights. Water should run down the side of the flashing and be directed to the shingles instead of finding its way into the roof deck.
If there were no flashing against these walls, water could slowly drip into the crevice between the wall and the roof, and potentially into the home.
Damaged or improperly installed roof flashing, especially around the chimney or dormer, is one of the most common causes of roof leaks. According to the Federal Emergency Management Agency, FEMA, improper roof flashing could lead to wood rot and even deck collapse. So, chances are, if you’ve been looking into your roof and its flashing, you have questions. What is roof flashing? How do you install roof flashing? What about repairing roof flashing? You can find out here.
There are almost as many types of roof flashing as there are parts of the roof! After all, each roof feature needs protection. These are the key types of roof flashing you need to understand:
Continuous copper flashing on a shingle roof
Types of roof flashing
While there are premade flashing pieces you can purchase, many roofing professionals will cut their own roof flashing from sheet metal. They’ll use tinning snips to cut the sheets and bend them to the exact size they need while on the roof. However, if you walk into a store to buy your own flashing, be careful. There are other types of premade flashing that are not made to be used on roofs and may break if you try to install them on a roof. For example, head flashing or cap flashing protects doors and windows from water.
If you intend to install or repair roof flashing, then you’ll need to pay attention to size. The flashing for your plumbing vent needs to be large enough to surround the vent, so it should be just wider than the vent’s diameter.
Further, your step flashing pieces need to be 10 inches (254 mm) long and at least 2 inches (50 mm) wider than the exposure of the shingle you’re using. For example, 3-tab shingles usually have a 5 5/8-inch (143 mm) exposure. Typically, 10- by 8-inch (253 mm x 203 mm) flashing is chosen. Those 8 inches are more than enough to cover the exposure of typical shingles. The same size can be used to cover the longer exposure on Nordic™ shingles.
However, if you were using IKO’s Crowne SlateTM, with a 10-inch (254 mm) exposure, you’d need a 10- by 12-inch (254 mm x 304 mm) step flashing piece.
In the past, roofing professionals would use lead, or lead-coated materials, as flashing. However, roofing professionals in North America now prefer other materials:
Building codes may demand your roofing professional use a specific material for flashing. They may also list a minimum thickness. Most building codes require 26-gauge galvanized steel as a minimum. You should always check your local codes to be sure you’re following them.
In fact, if you live in Florida, you may find that your building codes call for a special flashing material, modified bitumen roofing tape:
When you install roof flashing, you will need to use a sealant. While roofing professionals occasionally use nails when flashing, they must choose whether to nail to the roof plane or the vertical wall. If nailed to both, the flashing may deform under the pressure from shifting brick or wood. When nailed only to the roof plane or vertical wall, the flashing can stay in place while the other building materials expand and contract throughout the seasons.
Roofing cement: Roofing cement creates a waterproof seal. Roofing professionals usually apply it with a trowel.
Before you learn how to install roof flashing, you need to understand that there are three primary techniques, each suitable for different areas on the roof. You’ll find that some types of flashing correspond to a specific technique.
Plumbing vent boot flashing
Disclaimer: Roof flashing should always be installed by professional roofers, who understand best practices, safety requirements and the building codes and laws in their area. These instructions are only to help homeowners understand what to expect from their roofing professional.
Step flashing is the most time-consuming of all flashing jobs on the roof because you must complete it step-by-step as you shingle up the roof. There are a few general best practices you need to know. First, step flashing must be installed before the siding, so that the siding can cover the top of the flashing. If this is a repair job, the siding must also be removed and replaced with the flashing. Second, step flashing needs to extend 8 to 14 inches above the shingles, according to the National Roofing Contractors Association (NRCA).
Also, before you start installing your flashing, you need to look to see if the wall in question has a corner on the roof face, as in the image below.
If it does, follow our first installation procedure. If it doesn’t have a corner, and simply looks like the image below, follow the second installation procedure.
Step roof flashing no wall corner
If a wall corner is on the rooftop, you will need to create a corner flashing piece using a typical step flashing piece. These instructions will tell you how to create a corner piece and how to install step flashing generally:
Roof shingle over step flashing
Step flashing on roof peak
If your roof face connects to the wall cleanly without creating a corner, then you don’t need to create a corner flashing piece. Instead, you will need to install kickout flashing to help guide the water into the gutter. While some professional roofers will make their kickout flashing by hand in copper, if you’re using galvanized steel, it will be too tough to bend properly. Instead, buy a premade kickout flashing piece.
Here’s how to install kickout and step flashing:
Chimney flashing should be installed at the same time the mason is laying the brick and mortar, or the roofer will have to cut a ridge out for the counter-flashing. Then, the roofer will have to seal this indent up, after placing the flashing.
Counter flashing on a chimney
Installing a roof plumbing vent is typically an easier task than flashing a chimney. Here is how you do it:
Do you need information about how to install the other kinds of roof flashing? IKO has already explained how to install drip edge flashing and how to install metal valley flashing.
Old roof plumbing vent flashing boot
New roof plumbing vent flashing boot
On a typical re-roofing job, where you are replacing an old or underperforming roof, it is wise to replace all flashing. Old flashing may begin to fail before the new roof’s lifespan is over. However, there are limited circumstances where a roofer may decide to reuse flashing. For example, if a roofer is doing a repair job on a relatively new roof and the flashing appears to be in good condition, it may be salvaged.
To decide whether or not your flashing can be reused, your roofer will need to remove the flashing carefully to prevent damaging it. Your roofer will then inspect it before deciding to reuse it. If your roofer is replacing the shingles around your flashing, the flashing must be removed, at least temporarily, to allow for proper installation.
Some types of flashing, like step flashing, may be more challenging to reuse because it is harder to separate from the old shingles without denting or otherwise damaging it. Typically, a roofer will replace step flashing on a new roof.
Also, your roofer should not layer new flashing on top of the old flashing. You should only have one layer of flashing on a roof at a time.
You might also wonder what damaged flashing looks like and when it should be replaced. Check over your flashing and look for:
If you find any of these problems, you may need to replace the flashing.
You may also wonder if you’ll need to replace your flashing when you’re having a new roof installed. That depends on a few factors. If the original flashing is in good condition and can be removed without damaging it, it is possible to reuse it. However, you’ll need to prioritize proper fit and seal over saving money if you want a watertight roof; so be prepared to purchase new flashing where needed.
Fixing roof flashing, just like installing flashing, is best left to roofing professionals. You should not take risks with your roof.
Though roof flashing isn’t the most dramatic element of a roof, it is one of the most important. If you find some flashing on your roof that you’re concerned about, we suggest you find a professional roofer through IKO’s Contractor Locator. A professional can help you solve all of your roof flashing problems or answer the questions you have about your specific roof.
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