A gambrel roof is very common on barn roofs and barn style homes. Installing flashing at areas where there is an interruption to the solid line of the pane, such as a vent pipe, roof edge, chimney, or wall is critical to avoid water leaking in at these junctions and water seeping into the roofing panels, which can cause water damage and rotting of the roofing materials and wood. The materials used to create the roof, whether shingle, tile, or metal all will need flashing underlaid at these points. Flashing is typically metal, copper or tin, and should be a continuous piece. For example, the join of a roof plane and a wall should have a continuous metal strip of flashing, bent at a 90 degree angle so that one side is flush against the wall and the other flush against the roof. Here you will find information on the steps to properly install flashing.
Step 1 - Prepare the Site
Any time you are working on a roof, you need to be extra cautious. Make sure that if you are on a high roof that you use safety ropes or harnesses. Prepare the site that will be receiving the flashing by pulling the roofing material (if already in place) back to expose the area up to six inches from the edge. If there is not yet any roofing present you don't have to worry about this step. Take care to preserve the roofing material (such as shingles) if you will be re-using it. Make sure it is clear of debris and that it is dry.
Step 2 - Install Flashing
Install the flashing working from the bottom up. Overlap (if needed) so that the top layer is the higher layer, and seal any joints with caulk or silicone to prevent moisture from seeping in at the joints. Flashing should extend out onto the plane of the roof or up the side of the wall or level at least four inches, but six is optimal. Take care with the edges of the flashing, as they will be sharp and can easily cut skin. Secure flashing in place every five inches with nails or screws. Galvanized fasteners are best as they will withstand corrosion. Make sure the flashing sits flush with the roof or wall. Make sure that the roofing material will overlap the flashing at transitions. Caulk any gaps or joints and allow the caulk twenty-four hours to cure. Flashing should also be installed at the edge of the roof to ensure moisture runoff.
Step 3 - Replace Roofing
Replace roofing, or install new roofing as appropriate. Relay shingles or sheets in the reverse order they were removed. Again working from the bottom up, the uppermost layer of roofing should overlay the lower. Secure the roofing with roofing nails or screws. A dollop of caulk under the edge of each layer closest to the flashing will help to secure the shingle edge and ensure it remains water tight.