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What is roof flashing?

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.

How to Repair Roof Flashing

Fixing roof flashing, just like installing flashing, is best left to roofing professionals. You should not take risks with your roof.

• Step One: Gently pry up the shingles surrounding or covering the damaged flashing. When working with step flashing, this may involve removing undamaged pieces of flashing as well.
• Step Two: Take your chisel and gently remove any asphalt cement you find.
• Step Three: If you caught the flashing problem before a leak began, there should be no damage to the underlying roof parts and structure. However, it’s important to check for damage anyway. If you find damage, then you will have to get it repaired before reinstalling the flashing.
• Step Four: Now, reinstall the new flashing and shingles. Be sure to follow the proper order, as described above, especially when installing step flashing, to ensure the flashing will stand up to water.
  

When to Repair a Roof Flashing Leak
You might also wonder when you should replace roof flashing. Check over your flashing and look for:

• Damage, holes or bending.
• Corrosion or rusting.
• Loose or missing nails.
• Dried out or missing sealant.
• Flashing that has come loose.

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.

Roof Flashing Materials

In the past, roofing professionals would use lead, or lead-coated materials, as flashing. However, roofing professionals in North America now prefer other materials:

• Aluminum: Aluminum flashing is easy for roofing professionals to form and is lightweight. However, aluminum must be coated if it is to be used with concrete and masonry, as plain aluminum reacts and degrades when it touches alkaline surfaces. In coastal areas, aluminum flashing should be coated even if it does not contact concrete or masonry, to prevent corrosion.
• Galvanized Steel: Galvanized steel is usually the material of choice for flashing. It’s malleable, has aesthetic value and, when galvanized, is corrosion-resistant.
  
• Thermoplastic: Thermoplastic roof flashings are durable and flexible, resisting UV radiation and extreme weather while being lightweight, easy to install, and simple to repair, thereby reducing overall costs and efforts.

How to Install a Roof Plumbing Vent Flashing Boot

Installing a roof plumbing vent is typically an easier task than flashing a chimney. Here is how you do it:

• Step One: Install shingles as normal up to the base of the plumbing vent.
• Step Two: Place the flashing or boot onto the plumbing vent, so the base is resting on shingles. Momentarily lift the boot and apply sealant to hold the flashing in place.
• Step Three: Firmly push the flashing back down into place.
• Step Four: Install the next course of shingles. When you reach the plumbing vent, allow the shingles to overlap the top of the flashing.
• Step Five: To make room for the vent itself, cut out a circular piece of the shingles, as shown below.
• Step Six: To secure the circular edge of the shingle, apply roofing cement beneath it. Ensure you also nail it where you normally would.