In this example, apron flashing is installed after the course of shingles immediately below the chimney is in place. The sides of chimney are flashed using pieces of base flashing installed with each course of shingles. The upper edge of each piece of flashing should extend 2 in. above each course of shingles. The lower edge should be 1/2 in above the butts of the shingles forming the next course. The base flashing must extend up the wall and onto the roof a minimum of 4 in.

The counter flashing is installed in a raggle left by the mason in steps as shown. Lead wedges or tension forming shapes are used to hold the flash ing in place and raggle is filled with a sealant.

The length of each piece of counter flashing will vary with the slope of the roof but no step should be more than 3 bricks high. The width will vary but should always be wide enough to cover 4 in. of the base flashing.