Many people who have porches attached to their homes have problems with water leaks at the junction of the porch and the exterior wall of the home. These leaks are almost always caused by improper flashing installation or the absence of roof flashing altogether. Flashing works like one long shingle to make the joint between the porch roof and the house impregnable. It isn't easy to install roof flashing correctly, but it can be done if you follow the rules closely.
Prepare the area where you will install the roof flashing. If you already have faulty flashing installed, you must remove it. If siding on the house wall abuts the porch roof joint, the lowest strip should be removed to install the flashing underneath.
Measure the length of the porch roof joint to determine how much flashing you will need. Typically, flashing comes in 3 m (10 foot) long pieces. If your roof joint is longer than that, you will need to have two or more pieces soldered together to make one long piece.
Choose the material for your roof flashing. Aluminium is a popular choice of do-it-yourselfers because it's easy to work with, but it is not of the highest quality. Tin, galvanized metal, sheet lead and copper are other options, with copper being the premium choice.
Cut the flashing to size with tin snips if the porch roof joint is shorter than the length of the flashing.
Use the metal break tool to bend the flashing lengthwise in the middle according to the angle of the roof joint. Most flashing is 20 cm (8 inches) wide: 10 cm (4 inches) should go up the house wall, and 10 cm (4 inches) should go on top of the porch roof tiles.
Make a 10-degree bend on the shingle edge of the flashing approximately 1.2 cm (1/2 inch) from the edge. Waviness in the metal can develop after cutting, and this bend helps keep the flashing straight while you are installing it.
Position the flashing in the joint between the house and the porch roof. The wall portion of the flashing should be flush against the exterior wall, and the shingle portion of the flashing should be on top of the porch roof shingles.
Nail the flashing into place using galvanized roofing nails. Keep the nails as close to the edges of the flashing as possible. Nailing in the inside of the flashing will ruin its impregnability.
Replace the siding on the wall over the flashing.
Single pieces of flashing can be used instead of one long piece if you overlap them carefully.
If your roof requires multiple pieces of flashing to be joined together, do not use aluminium flashing. Aluminium cannot be soldered, and there is no other method of joining the pieces as effective as soldering. Don't use aluminium if your home is made of stucco or masonry because it will corrode faster. Always wear gloves when working with flashing because the edges are very sharp.