The Do's and Dont's of Shingle Flashing and What to Look For - The Exterior Company

The Do’s and Dont’s of Shingle Flashing and What to Look For

Shingle flashing refers to the thin pieces of weather-resistant metal installed on specific sections of a roof to prevent water from entering the structure. Flashing works by directing pooling water away from the area and is often a feature of roof valleys, chimneys, vents and skylights. Several materials work well for flashing, such as aluminum, copper, lead or galvanized steel.


Although flashing is a handy weatherproofing feature, it requires careful installation to be effective. This guide will teach you about the different types of shingle flashing and provide many helpful tips on proper flashing installation.


Roof Edge Flashing Types

There are many parts of a roof — and a type of flashing designed for almost every part. Below are the most common types of shingle flashing.


  • Continuous flashing: Continuous flashing, also known as “apron flashing,” is a single long piece of metal that carries water to the shingles below. Long strips of continuous flashing may have trouble flexing as the house contracts and expands over the years and, if left as is, could warp or even break. For this reason, long pieces of continuous flashing come with expansion joints, which enable them to move with the house.
  • Base flashing: Some features on roofs, such as chimneys, require two pieces of flashing. There are multiple reasons for a two-part system. It will ensure rain always hits a surface of flashing that directs it downward, it can better deal with the expansion and contraction of the roof and it’s challenging to install a single piece of flashing around chimneys, anyway. Base flashing refers to the bottom piece of this two-piece system.
  • Counter-flashing: Counter-flashing, placed above or opposite to base flashing, is the other component of this two-part system.
  • Step flashing: Step flashing refers to a rectangular flashing piece bent 90 degrees in the center. It’s best to use for roof-to-wall flashing. Multiple pieces of step flashing get installed in layers with shingles, which ensures all water flows away from the wall.
  • Skylight flashing: Although some skylight products come with flashing, in many cases, roofing professionals have to make it or buy it separately.
  • Valley flashing: Valley flashing protects the open valleys of roofs, which are vulnerable areas.
  • Drip edges: Edges of roofs feature thin metal flashing that allows water to drip off the roof without causing water damage to the home.
  • Kickout flashing: Roofers need a component to bridge the gap between the end of the step flashing and the beginning of the gutter. Kickout flashing serves to direct water away from the wall of the house and into the gutter.

Shingle Flashing Installation and Repair

Below are several short tutorials on installing metal flashing on a roof.

Disclaimer: Roofing professionals who are well-versed in the best safety requirements, practices and building codes in their area are the only people who should perform shingle installations. These instructions only serve to help you understand what you can expect from your roofing professional.


We’ll begin with how to install step flashing, which is the most time-consuming and challenging part of the installation because it requires step-by-step installation alongside the roof shingling.


When installing step flashing, keep the following in mind.


  1. Step flashing needs to get installed before the siding: Doing this will allow the siding to cover the top of the flashing. If you’re getting your step flashing repaired, the installers will have to remove and replace the siding along with the flashing.
  2. Step flashing must reach eight to 14 inches above the shingles: The National Roofing Contractors Association stipulates this requirement.


Also, before beginning any step flashing installation, you must find out whether the wall has a corner on the roof face. If it does have a wall corner, follow our first procedure. If not, follow our second one.


Installing Step Flashing With a Wall Corner

If there is a wall corner on your rooftop, you will have to make a corner flashing piece using a normal step flashing piece. Read these instructions to learn how to create a corner piece and install step flashing as usual.


  1. Install your underlayment and shingles up to where the wall starts: This step will ensure the first flashing piece, or the corner flashing, will rest on top of a shingle.
  2. Make corner flashing: Take some tin snips and cut a 45-degree line from a corner on the outside to the center fold. Once you’ve done that, cut along the center fold and take out the triangle that results. Doing so will enable you to cleanly bend the step flashing around the corner. If you’d rather not create corner flashing on your own, you can instead buy pre-bent pieces, which you can cut to size. You can also buy pieces of corrugated aluminum, which are easier to bend.
  3. Bend the corner flashing around the corner tightly: Make sure it’s sitting flat and extends a minimum of eight inches above the shingles. Then, secure it with a nail on both sides of the top edge.
  4. Set down a second piece of flashing: Take another flashing piece and set it in place. Bend it back so it overlaps the corner flashing.
  5. Apply sealant: Take out the second piece and apply sealant where the step flashing will overlap. Then, set the flashing piece back down. Hammer a nail to the flashing’s bottom, and make sure it’s high up so the next row of shingles will cover it.
  6. Continue with the shingles: Finish an entire course of shingles above this flashing piece.
  7. Apply another piece of step flashing: This piece goes where the next shingles course will begin and it must overlap the last flashing piece by a minimum of three inches. Apply some sealant where the flashing’s base will sit, and then set the flashing in place.
  8. Keep alternating between shingles and flashing: Do this until you get to the top of your roof.
  9. Flash the peak of your roof: To flash the peak, you’ll need to make another custom flashing piece. To do this, take a regular piece of step flashing and cut into its fold roughly halfway.
  10. Bend the other side to match the roof’s peak: Leave one side of your cut piece straight. Then, secure this piece by applying roofing cement and driving one nail into the base. Later, you will cover it with a ridge shingle.

Installing Step Flashing Without a Wall Corner

If the face of your roof cleanly connects to your wall without making a corner, then there will be no need to make a corner flashing piece. You will instead have to install kickout flashing, which will help direct the water into the gutter below. If you’re using copper flashing, it may be possible to make kickout flashing by hand, but if you’re using galvanized steel, bending it properly will be difficult. In this case, you should purchase a pre-made piece of kickout flashing.


Follow these steps to install kickout and step flashing.


  1. Place the kickout flashing on the roof’s base: Make sure it is snug against the wall. Then, take the piece out briefly and apply some roofing cement where it will rest.
  2. Place your first step flashing piece: Put the first step flashing piece over the starter strip’s end, making sure it leads directly into the kickout flashing. Then, secure it to the roof deck with roofing cement and two nails. The nails should go on the base of the step flashing, so you’re driving them into the deck. You should also place the nail high up, so the next shingles course will cover them up.
  3. Apply a shingle: Once you’ve secured the kickout flashing and first step flashing piece, you will need to apply a shingle. First, apply some sealant to the flashing’s base. Then, place a shingle on top of the flashing a nail it down as usual. Ensure the shingle’s bottom covers up the nail and the base of the flashing.
  4. Finish the entire course of shingles.
  5. Complete the step flashing: To do this, follow the procedure described above, starting at Step 7.

Installing Counter-Flashing on a Chimney

Chimney flashings require installation at the same time the mason is laying the bricks and mortar. Otherwise, the roofer will need to cut out a ridge to accommodate the counter-flashing and seal this indent after placing the flashing.


Follow the steps below to install counter-flashing on your chimney.


  1. Check the base flashing: Make sure the base flashing of your chimney is underneath the shingles and secured to your roof according to the manufacturer’s recommendations. If you do not have base flashing, you can install step flashing up the chimney’s side.
  2. Make an indent in the chimney: You can do this by cutting with a bit saw or diamond grinder disc. The counter-flashing will hang from this spot.
  3. Lay the counter-flashing into the indent: Ensure the counter-flashing hangs so there is at least a two-inch overlap with the base flashing.
  4. Secure the counter-flashing: Secure to the chimney and the base flashing with roofing cement.
  5. Seal the indent: Do this with roofing caulking, which will allow the counter-flashing to hang securely.

Installing a Roof Plumbing Vent Flashing Boot

This installation is generally more straightforward than flashing a chimney. Follow this procedure to install a flashing boot for a roof plumbing vent.


  1. Install shingles in the usual fashion until you reach the plumbing vent’s base.
  2. Place the flashing boot: Put the flashing boot on the plumbing vent so the base rests atop the shingles. Then, lift the boot briefly so you can apply sealant, which will hold the boot in place.
  3. Push the flashing boot firmly back down into place.
  4. Install the next shingles course: When you get to the plumbing vent, let the shingles overlap the top of the flashing.
  5. Make room for the vent: Do this by cutting out a circular piece of the shingles.
  6. Secure the shingle’s circular edge: Apply roofing cement underneath it, and also ensure that you nail it where you normally would.

Shingle Flashing Repair

You may also wonder when to repair or replace your roof flashing. Check your flashing for any of the following signs:


  • Rusting or corrosion
  • Damage or holes
  • Bending
  • Nails that are loose or missing
  • Loose flashing
  • Sealant that has dried out or is missing


If you notice any of the above common flashing problems, you may have to fix or replace your flashing.


You might also wonder whether you’ll have to replace the flashing if you’re replacing an old roof. If the original flashing is still in decent condition, and removing it will not do any damage, you may be able to reuse it. However, there is a chance the old flashing will not fit properly on specific sections of the new roof, so you should be prepared to buy new flashing wherever necessary.


Here’s how to go about repairing your flashing. Just like with installing flashing, it’s best to leave these repairs in the hands of roofing professionals.


  1. Remove shingles near or on the damaged flashing: Pry up the shingles gently. If you’re repairing step flashing, you may have to remove some undamaged flashing pieces as well.
  2. Remove any asphalt cement you see: It’s best to do this step with a chisel.
  3. Check for damage: If you noticed the flashing issue before a leak occurred, there shouldn’t be any damage to the underlying roof structure. However, you should look for damage anyway. If you notice any issues, you’ll need to get those repaired before you reinstall the flashing.
  4. Reinstall the new shingles and flashing: Make sure to follow steps in the right order, as described above. It’s especially crucial to do so when you install step flashing.

Common Incorrect Installation of Roof Flashing and How to Fix It

Improperly installed roof flashing can lead to a leaky roof, which will require immediate repairs. While you can DIY some roof flashing repairs using a patching material purchased from your local hardware store, we recommend you contact a roofing professional for fixing leaks on a roof. Also, regularly inspecting your roof can help you identify any areas of concern in your flashing before they become a severe problem.

Can I Get Flashing Fixed Without Replacing My Whole Roof?


Tiny holes or corroded spots in the flashing are a relatively easy repair. Plug pinholes with roofing cement, and patch holes up to 3/4 inches in diameter with patches made from the same material as your flashing.

To do this, you’ll first need to roughen the area surrounding the hole using sandpaper or a wire brush, then clean it. Then, cut a patch larger than the hole and attach it using roofing cement. Finally, cover the patch using more roofing cement.

Significantly corroded flashing requires replacing. To do this, you’ll need to remove several shingle rows in addition to the old flashing.


You can renew flashing seals by chipping out the existing mortar and then caulking along the flashing’s edges. To seal the joints between the chimney and the flashing, use a special masonry caulk.


To seal the seam between the step flashing and cap, use silicone caulking compound or urethane roofing cement. When working with valley flashing, you will need to lift the edges of surrounding shingles and then spread roofing cement on the flashing roughly six inches from the shingles’ edge.


If you need to reseal drip edging, you should only seal under the shingles — do not seal the drip edge flashing along the eaves.


If you’re replacing the flashing for the vent pipe, the first thing you should do is take off the shingles that cover the flange on the sides and in the back. Then, gently pry and lift the flashing off. Cut off or pull any nails. Then, place new flashing for the vent pipe on top of the vent, push it into place and nail where the shingles will cover it. Finally, replace your shingles, then cover the nails using roofing cement.


What Happens With Improper Flashing Installation?


Here are some roofing problems associated with improperly installed flashing.


  • Blow-offs: Open joints and seams eventually lead to blow-offs, where sections or all of your roof blows away.
  • Billowing: Billowing takes place when large areas of the membrane become detached and begin to flutter in high wind.
  • Tenting: Tenting refers to the phenomenon where the dimensional shortening of the roof membrane leads to roof shrinkage.

Contact The Exterior Company, Inc., to Install or Repair Your Shingle Flashing


The Exterior Company, which serves all of Central Pennsylvania from our home base in Lancaster County, is your go-to company for all roofing repairs and maintenance. Get in touch with us today to request a consultation.

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