When building an addition on the home, roof flashing must be installed in the roof valleys and to connect the old roof with the new one. Proper installation of flashing permits rainwater to run off the roof of the house in the correct manner. Flashing should always be installed before installing roofing material.
You will need:
Step 1: Measure the amount of flashing needed for the new roof and purchase the desired type of flashing. The most popular material used for flashing is aluminum but sheet lead, premium copper, galvanized metal, and 20 to 40-pound tin are also available. Aluminum flashing should not be used when soldering multiple pieces of flashing because it cannot be soldered. Wear protective eyewear and gloves if you will be soldering.
When calculating measurements, allow for an overrun of 10 to 15 percent and some extra in case a measuring or cutting mistake is made. Flashing is typically sold in 10-foot lengths. You can use shorter pieces of flashing rather than a single long one if you overlap the shorter pieces by two inches.
Step 2: If a repair is being made in a roof valley, remove the roofing materials down to the planking prior to installing the flashing. The valley must be clean and dry. If a room addition is being attached to an existing roof, remove one or two rows of shingles from the original roof, keeping the felt paper and tar intact. In addition, you may want to remove top siding from the addition or the home prior to installing the flashing.
Step 3: Use the tin snips to cut flashing to the required length. If you are connecting two roofs, bend the flashing in the middle, using the metal break tool to correspond with the angle of the joined roofs. Flashing material usually has a width of eight inches so each roof should have four inches of flashing.
Step 4: Install the flashing where it is needed, aligning the middle of it with the grove in the valley. Ensure that half of the flashing is installed on both sides of two roofs being adjoined.
Step 5: Secure flashing to roof planking with the staple gun. Staples should be inserted down each side of the flashing, one inch from the edge of the material.
Step 6: After installing flashing in a roof valley, the roofing material should be replaced to create a waterproof barrier. Before installing shingles, apply roofing tar to provide additional protection against water backing up on the roof. When tying in two roofs, finish the new roof and install fascia board.