Roof flashings are an integral part of any roof system. There are many different types of flashing designs such as step flashing, saddle flashing, drip flashing, vent flashing, continuous flashing, etc. Each flashing design has a particular function in protecting the home envelope from water damage. Chimney flashing is a combination of step flashings and counter flashings. Replacing chimney flashing begins with a detailed inspection of the roof surfaces. Look for rotted wood, deteriorated shingles, or shingles that have lifted up, corroded flashings, flashings that have pulled away from the roof plane or the vertical surface, and deteriorated chimney brick or mortar joints. Make all the necessary repairs prior to replacing the chimney flashings.

Preparation  

Properly installed chimney flashings contribute to the integrity of the roof.

 

1. Remove the shingles at least 18″ from the chimney vertical surfaces all the way around. Lift the lower edge of each row of shingles with the aid of a thin crowbar. Pull the roofing nails that hold each row of shingles down. 
2. If the chimney has counter flashing, rake the mortar out of the joints at the very top edge of the counter flashing all the way around until you hit the metal flashing inside the mortar joints.
3. Remove any nails holding the counter flashing in place and remove the flashing.
4. Remove the nails in the side of the chimney that hold the step flashings in place. 
5. Remove the step flashings.

Installing the new base flashing

1. Cut a piece of flashing material that is longer than the width of the chimney. 
2. Fold it in the middle lengthwise.
3. Mark the width of the chimney on the flashing material starting from the middle of it.
4. Cut in from the top edge half way down to the bend at the edges of the chimney width markings.
5. Lay the flashing in place across the lower edge of the chimney. 
6. Secure it in place with nails installed into the chimney, not the roof.
7. Bend the tabs that were cut out down against the roof.

Installing the step flashings

1. Place the first step flashing in place at the lower edge of the chimney along the side overlapping the base flashing tabs.
2. Replace the lowest course of shingles. 
3. Install the next step flashing, followed by the next course of shingles which should overlap the step flashing at that point.
4. Follow this pattern, installing the step flashings up the side of the roof.

Installing the top flashing

1. Bend and cut the top chimney flashing to the same dimensions as you did the base flashing except cut from the bottom edge instead of the top edge.
2. Lay the top flashing in place and fasten it to the side of the chimney with nails.
3. Bend the tabs down against the roof. 
4. Finish installing the step flashings and the final courses of shingles.

Installing the counter flashing

1. Cut the counter flashings to match the length of the sides of the chimney. Cut the ends at an angle to match the angle between the side of the chimney and the slope of the roof.
2. Place the L angle side of the counter flashing into the empty mortar joint so that the lower edge of the counter flashing overlaps over the top of the step flashings.
3. Remortar the joints of the chimney where the counter flashing fits to seal each joint watertight.
4. Examine the flashings carefully and seal each joint where flashings meet each other, the chimney, or the roof surfaces with a good quality roof cement or silicone caulk. Force the cement or caulk into the joints with your fingers then add a generous amount over the top of the sealant and trim it with a putty knife.

Moss and algae form on roofs when moisture is present or lingering and the humidity is high. These organisms are difficult to remove and can damage roofing materials over time. The moss root system grows under the tabs of asphalt shingles and raises them allowing water to enter and damage the roof substrate causing dry rot.
Algae do not harm the roof, in general, but cause unsightly black stains. There are three main methods of removing moss and algae. These are mechanical, chemical, and wash down. Which method you use depends on how rapidly you want to dispose of the moss, the type of roofing material you have, and whether or not you have access to the roof of your home.

Mechanical

1. You can sweep the moss off the roof with a stiff bristle broom or brush if you have access to the roof. Sweep downward, not across the shingles or upward. Protect the shrubbery alongside the house with a tarp or plastic sheeting
2. Pressure washing is also a good cleaning alternative but keep the water pressure extremely low or you will damage your roofing material. You should be able to place your hand in the pressure stream without discomfort.

Moss and algae can damage a roof

Chemical

1. There are many different chemicals for moss removal. Some are harmful to the environment and some are biodegradable. Check the label and follow the manufacturer’s instructions.
2. In general, apply the chemical to the moss and wet it thoroughly. Allow the chemical to sit on the moss for the prescribed amount of time, then brush the dead moss off carefully with a stiff bristle broom or brush in a downward motion.
3. You can also flush the dead moss away with a stream of water or simply allow rain to do it for you.
4. Protect the shrubbery at the base of your house and keep in mind the effect the chemicals may have on your gutters, asphalt shingles, ground water, and pets.

Washdown

1. Use a stiff bristle brush to loosen the moss and then a garden hose or pressure washer under very low pressure to wash it away.
2. Once again, sweep the moss, and direct the water only in a downward direction to avoid lifting the shingle tabs or damaging the shingles.
3. You can install strips of copper or zinc sheeting under the top row of shingles near the peak of the roof. Rain will wash the metal particles down the roof and kill the moss and algae over time.

Tips

No matter which method you use, observe all safety precautions: wear a safety harness or tie yourself off with a strong rope. Wear good shoes or boots with a strong high traction sole. Stay away from the edge of the roof.

Unless your roof is very flat or you are a professional roofer, it may be best to hire a roofer or roof cleaning professional to avoid injury to yourself or the roof.