Expert advice on how to repair roof flashing and chimney flashing, prevent ice dams, and solve other roof flashing problems.

When a roof leaks, the problem is often due to leaks in and around the metal roof flashing that protects roof edges, valleys, and the junctions between roofing and obstructions such as chimneys, dormers, and vent pipes. Here we look at how to repair flashing that can cause leaks.

How to Repair Roof Flashing

Diagram of roof flashing types including chimney, continuous, drip edges, skylight, step, valley, and vent pipe.
Various Types of Roof and Skylight Flashing © Don Vandervort, HomeTips

The methods for repairing roof flashing depend upon the particular problem.

Repairing Small Holes in Roof Flashing

Step 1: Roughen the area around the hole with a wire brush or sandpaper.

Step 2: Clean the area thoroughly.

Step 3: Cut a patch larger than the hole from the same material as the flashing.

Diagram of a patch affixed with roof cement on a chimney’s base flashing.
Patch flashing with the same material as the flashing set in asphalt cement.

Step 4: Affix the patch with roofing cement.

Step 5: Cover the patch with more roofing cement.

Replacing Damaged Flashing

Flashing that is badly corroded will need to be replaced.

1. Remove Shingles and Old Flashing

Step 1: Remove several rows of shingles to access the old flashing.

Step 2: Remove the old flashing.

2. Install New Flashing

Step 1: Position the new flashing.

Step 2: Nail the new flashing in place.

Step 3: Replace the shingles and cover the nail heads with roofing cement.

Renewing Flashing Seals

The method and material for renewing flashing will depend upon the type of flashing and its location. 

1. Renew flashing seals at a chimney

Step 1: Chip out the old mortar and caulking along the edges of the flashing.

Step 2: Use special masonry caulk to seal the joints between the flashing and the chimney.

Step 3: Seal the seam between the cap and step flashing with urethane roofing cement or silicone caulking compound.

Illustration of step flashing around corners of a roof, including seams sealed with caulking.
Seal step flashing with urethane caulking.

2. Sealing Valley Flashing

Step 1: For valley flashing, lift the edges of the surrounding shingles and spread roofing cement on the flashing about 6 inches in from the edge of the shingles.

Step 2: Press the shingles down into the roofing cement.

4. Sealing Drip Edging

For drip edging, seal the upper edge beneath the shingles with roofing cement but do not seal the drip edge along the eaves.

Replacing Vent Pipe Flashing

Step 1: Remove the shingles covering the flange of the vent pipe flashing at the back and sides.

Step 2: Pry and lift off the flashing.

Step 3: Remove any nails.

Step 4: Position the new vent-pipe flashing over the vent, push it down into place, and nail where shingles will cover it.

Step 5: Replace the shingles and cover the nail heads with roofing cement.

Are Ice Dams Causing Leaks?

Leaks from ice dams are related to flashing problems—when ice dams occur, the flashing and roofing along eaves fail to prevent water from making its way up underneath the roof covering materials. For information on how to prevent ice dams, please see “How to Prevent Ice Dams.

How to Maintain Roof Flashing

Diagram of roof flashing types including chimney, continuous, drip edges, skylight, step, valley, and vent pipe.
Types of Roof Flashing ©Don Vandervort, HomeTips

Here are a few suggestions for care and maintenance of your roof flashing.

1. Preventive Tips

Step 1: Check the flashing as well as the condition of your roof shingles regularly.

Step 2: Look for loose nails and holes as well as the seals at the edges of the flashing.

Step 3: Reseal the flashing as needed using roofing cement and caulking.

2. Painting New Flashing

Step 1: Use a stiff brush and solvent to remove flaking paint, corrosion, and dirt.

Step 2: Apply a zinc-based primer and then spray on two or more light coats of rust-inhibiting metal paint.

3. Dormer Flashing

Step 1: Scrape out old caulking compound if any.

Step 2: Brush the flashing with a wire brush.

Step 3: Apply urethane roofing cement between the siding or shingles and the flashing.

Step 4: Seal any obvious seams.

About DIY Roof Repair

Unless your roof’s pitch is relatively low and you have the necessary experience, tools, and confidence to get the job done safely, be wary of doing your own roof repairs—working on a roof can be dangerous. It may be best to leave this work to a professional.

If you decide this is the case, please see our affiliate partner, HomeAdvisor, to receive free bids from local asphalt shingle roof repair pros.

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About Don Vandervort
Don Vandervort has developed his expertise for more than 30 years as a remodeler and builder, Building Editor for Sunset Books, Senior Editor at Home Magazine, author of more than 30 home improvement books, and writer of countless magazine articles. He appeared for 3 seasons on HGTV’s “The Fix,” served as MSN’s home expert for several years, and is featured as Yelp's home improvement expert. Don founded HomeTips in 1996. Read more about Don Vandervort