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While roofs are purposely constructed to allow rainwater run-off, they can often have several vertical features or protrusions, such as chimneys, parapet walls, half walls, dormers, skylights, vent pipes, and the like, where water can pool up and/or drip into the crevices between. The areas can eventually become damaged and allow water seepage and leaks into the house. To prevent this, professional roofers apply roof flashing to divert rainwater down the sides of the vertical surfaces, keeping the water from stagnating.
Flashing closes the joints between the roof and the roof features in order to protect the house from erosion and leaking. A lack of flashing or poor flashing installation can also lead to wood rot, potential shingle damage, or deck collapse, among other issues. For installation, the roofer will have to choose between nailing the flashing or using a sealant. As professional roofers may explain, nailing can involve some risk. If flashing is nailed to both the roof plane and the vertical surface, it can cause the flashing to deform from the pressure of shifting brick or wood.
The flashing will stay in place when nailed properly to only one of the surfaces, but nailing can create unnecessary holes in the roof structure. An alternative that professionals use is roofing cement, which creates a waterproof seal between the roof and the flashing. Flashing comes in various shapes and is used for different areas on the roof. For this reason, different flashing types will be installed in dissimilar ways, and the cost of flashing will vary.
If the homeowner is uncertain about having flashing installed, it should be noted that alternative materials, such as sealant or tar, are ineffective long-term. They break down, making the areas they are purposed to protect vulnerable to water. Flashing, on the other hand, is made for long-term use and, when installed properly, keeps the roof from blemishes and damage.
Types of Flashing
Flashing is vital for specific areas around the roof: where the roof abuts a wall, low points where two roof slopes converge (called valleys), roof protrusions (such as skylights) and roof edges (called rakes and eaves). Flashing is shaped into various designs depending on where it is needed along the roof.
There can be a wide variety of names assigned to each flashing style, but the list boils down to the following:
Roof Flashing Types
- Continuous Flashing. This is also known as “apron flashing” because it acts in a similar manner to an apron. It is a long, single piece of metal that is used to carry the water down to the shingles that lay below.
- Base Flashing. There are some roof features, like chimneys, that require two pieces of flashing. This is to ensure that the rain always meets a flashing surface to direct it downward. Not only that, it is notoriously difficult to install flashing around a chimney.
- Counter Flashing. This is placed opposite of base flashing, or above the base flashing. Counter flashing completes the team with the aforementioned base flashing.
- Step Flashing. This is a rectangular piece of flashing that is bent 90 degrees in the middle. It is generally used for wall flashing. In this instance, multiple pieces of flashing will be installed as layers with the shingles to make sure that the water flows away from the wall.
- Skylight Flashing. There are some skylight manufacturers that include flashing with their product, but others will require you to create it or purchase it separately. Knowing which option you have beforehand is helpful.
- Valley Flashing. Any open valleys on your roof have metal flashing in order to protect this area, which is a critical area of the roof.
- Drip Edges. At the edge of the roof, there is a thin metal flashing that allows water to drip off the roof without doing damage to the home or causing a pesky leak that can do further damage to the roof or home.
- Kickout Flashing. Roofing contractors generally need something to bridge the gap where the step flashing comes to an end and where the gutter begins. This kind of flashing is used to direct water away from the wall and down into the gutter.
There are also a few different roofing materials that you need to be aware of. In the past, this would be lead or materials that were lead-coated. Now, professionals throughout North America have switched to one of three materials.
Roof Flashing Materials
- Aluminum flashing is generally easy for roofers to form and it is also quite lightweight. There is one thing to note, however: aluminum has to be coated if it is going to be used with masonry and concrete since plain aluminum degrades and reacts when it makes contact with alkaline surfaces.
- Copper roof flashing takes soldering well and is also malleable. Not only that, it is highly durable and tends to have a longer-lasting life. On the other hand, there is some discoloring into patina, which can vary based on the homeowner. Copper flashing is routinely found around chimneys.
- Steel flashing is the most popular choice for flashing. In addition to aesthetic value, it is also malleable and, when galvanized, is corrosion-resistant.
There are building codes to be aware of that may call out a specific material. Have your roofing contractor look into this so that you can be covered in the event that a certain material is disallowed.
Identifying Roof Flashing Types
There are quite a few types of roof flashing; nearly as many as there are parts to the roof. Each roof feature requires protection, hence why there are so many different types of roof flashing. Longer pieces of continuous flashing have trouble flexing as the home contracts and expand during the changing of the seasons. If left alone, it could warp or break and fail to keep that water out. If using longer pieces, they should have built-in expansion joints so that they can move as the home does.
Another benefit to two-part flashing is that when the roofing materials expand and contract with the weather, those two pieces can move, so the system stays secure. How do you properly install roof flashing? Here are a few helpful techniques.
Roof Flashing Techniques
- Step Flashing: The best instance for step flashing is where the roof face meets a wall. An example of this is where the dormer projects out from the roof. In a spot like this, it is entirely possible that water could flow down the wall and get past the shingles into the building down below.
- Plumbing vent boot flashing: To put it simply, vent flashing has a cylindrical piece of flashing. This piece of flashing fits around the vent itself. These shingles are installed over the base or the boot. The height of the boot is meant to force water to run around the vent itself.
- Counter Flashing: Counter-flashing is commonly used to flash chimneys and involves two flashing pieces. The first piece, the base flashing, is meant to sit around the base of the chimney. The second piece, the counter-flashing itself, finds itself embedded in the chimney’s masonry. This piece sits over the base flashing. It ensures the water doesn’t slip in behind the base flashing. Professional contractors generally use counter-flashing for a litany of other purposes, but it typically involves a second piece of flashing that is set off from the first.