Cap flashing, which is installed atop the head casing, is a window’s first line of defense against water infiltration. When bending cap flashing, I like to use 20-oz. copper for both appearance and durability. Unlike aluminum, the folded copper ends can be soldered, so I don’t have to rely on caulk to seal the joint. I use 20-oz. copper because it is thin enough to work easily yet provides protection far beyond my lifetime. I use a portable sheet-metal brake, which can be rented at most home stores, to bend the flashing’s profile.
For the soldering work shown here, I use a propane soldering iron (as opposed to a torch) because an iron offers me more control over the heat, which I apply to the copper fold. You also can buy electric soldering irons at most hardware stores.
Prior to soldering the ends, I apply flux to the flashing. Flux enables the solder to adhere to the copper. I also mix 1 part Ruby flux ($4.95 for a pint) and 3 parts water in my dipping jar, which I use to keep the iron clean.