How to Relead a Chimney

Remove old flashing. Use a crowbar to pry off the old lead. If necessary, use a masonry chisel to break the seal between the flashing and the chimney, and to remove any roofing cement. Remove all loose mortar, pieces of cement or other debris that might keep the new flashing from providing a tight seal.

Apply roofing membrane. Place 1 foot wide strips of self-adhesive waterproof roofing membrane around the entire base of the chimney, so that they overlap the bricks by approximately four inches. Place a strip 3 feet wide across the area above the chimney, to prevent leaks on the uphill side. Chimneys situated on the very peak of the roof do not require this extra piece of membrane.

Install base flashing. Use a pair of sheet metal snips to cut a piece of pre-bent lead base flashing to the same width as the front of your chimney. Cut a 45 degree angle in each end to accommodate the slope of the roof. Secure this piece of flashing to the roof using a hammer and roofing nails. Put a small blob of polyurethane roof sealant at the base of the 45 degree angle.

Install step flashing. Cut one piece of pre-bent step flashing to allow the end to bend about 1 ½ inches around the front of the chimney. Place this piece at the lower end of the side of the chimney, allowing its front corner to overlap the base flashing you already installed. It should cover the dot of caulk, sealing the potential leak where you cut the flashing. Secure this piece of flashing with roofing nails.

Install the remaining step flashing, working your way up the chimney until you have covered the first side completely, and then back down the other side. Make sure the bottom of each piece of lead flashing sits under the corresponding course of shingles. Each piece of step flashing should also overlap the one below it, so that water runs down onto the shingles and away from the chimney.

Install the cricket. This piece of lead is also known as the saddle and keeps water running down from the top of the roof from pooling above the chimney. Place the pre-bent saddle on the uphill side of your chimney, so it overlaps the last two pieces of step flashing. Secure it using roofing nails, then apply waterproof membrane to all of the edges.

Cover the cricket. Apply shingles over all parts of the cricket that rest on the roof. Cut them along the groove of the cricket, so that only about 2 inches of metal remain exposed.

Prepare the cap for flashing. Use the grinder to cut a 1 inch deep groove into the chimney mortar just above the top of the base flashing. Brush away all dust and pieces of mortar.

Install the cap flashing. Cut the cap flashing to the same width as the front of the chimney, pushing the bent end into the groove in the mortar. Repeat for each piece of step and cricket flashing, making sure that the metal is wide enough to completely cover the top of the base flashing with an overlap of about 2 inches. Fill the groove with polyurethane sealant to secure the flashing and keep water from running between it and the chimney.