Flashing helps to keep water from entering a house around a chimney. If water enters through cracks, seams or gaps and makes its way into a house, water can cause mold, mildew and wood rot. All three conditions threaten the structural integrity of the house because the wood becomes soft and loses its strength. Mold and mildew are dangerous for those in the home. Some molds are toxic, while others are irritants. Mold and mildew also leave the home smelling musty and old.


Roofers use a variety of materials as flashing including aluminum, copper, heavyweight felt paper, many layers of tar paper or sheet metal. Keeping the flashing tightly sealed to the roof and chimney stops the water from entering the house. Chimney flashing extends from the roofing material up the chimney to form a tight seal. Over time, exposure to hot and cold temperatures, snow, wind, ice and rain the flashing may crack or separate from the chimeny. Once the flashing develops cracks or pulls away from the base of the chimney, it is no longer an effective barrier. Keeping your flashing in good repair will save you money in the long run. Repairing flashing can be accomplished successfully by a do it yourself homeowner with the need for a professional roofer, which is another money saver.

 Safety When Working on a Roof

Tie off on safety lines to keep yourself safe on the roof.

Set up an extension ladder or scaffolding so you can reach the roof safely. If you are using an extension ladder, have a helper on the ground foot the ladder.

Set up ladders on level even ground. Do not set up a ladder on mud, loose gravel or on stairs.

Do not set an extension ladder against a window. The added weight and pressure will cause the ladder to crash through the window.

Do not work on a roof if there is snow, or ice on the roof.

Do not work on the roof while it is raining or when its dark outside.

Fixing the Flashing

Brush the dirt, dust and debris away from the base of the chimney will a small whisk broom or stiff paintbrush.

Examine the base of the chimney for cracks, splits, gaps or missing sections of flashing.

Pour asphalt roofing cement in a shallow, disposable pan or you can use a squeeze tube or tube of roofing cement that fits into a caulking gun.

Dip a trowel into the roofing cement and spread a thick layer over the damaged areas extending onto the roof and up the chimney. If you are using a squeeze tube or roofing cement in a caulking gun, make four to six thick lines of roofing cement over the damage and up the chimney and onto the roof.

 Press the roofing cement into the existing flashing with a trowel. Let the roofing cement set for five minutes or so.

Apply a thick layer of roofing cement over the flashing and about 2 to 3 inches out onto the roof and up the chimney until you touch the first mortar joint with roofing cement.

Spread and press the roofing cement into the roof and chimney with your trowel. As you get to the edge of the roofing cement, press it down very firmly to create a watertight seal. Make the edges of the repair thinner and thinner which is called feathering. Feathered edges will adhere to the existing roof and chimney better than a thick edge.


Check you’re the flashing around the chimney every fall and spring.

If the flashing is severely damaged, it will have to be replaced. No amount of roofing cement will keep a tight seal.

If there are gaps between the flasshing and roof or chimney greater than about 1/2 to 1 inch, replace the flashing.

Do not keep layering on roofing cement because you will end up will a very thick glab that won't protect your house from water damage -- only repair the damage.