The flashing was a strip of metal bent into the joint where the roof met the wall. Copper or lead or tin folded by hand and tucked under the shingles and up against the brick. The flashing sealed the gap. Every building has gaps where two materials meet and every gap is a door the water wants to walk through. The flashing was the lock on that door.

The flashing was bent on the job. The roofer took a flat sheet of copper and bent it over the edge of a board with his hands. No machine. The bend had to follow the angle of the joint exactly because the joint was never perfectly straight. The roofer read the joint the way a tailor reads a shoulder. Every joint was different and every piece of flashing was custom. The roll of self-adhesive membrane they sell at the hardware store is one size. One size does not fit anything. One size fits nothing well.

The copper flashing turned green. Twenty years of rain and sun and the copper oxidized and the green was the building's patina. The green said this flashing has been here long enough to change color and the building has been dry the whole time. New copper is bright as a penny. Old copper is green as a statue. The aluminum flashing does not change color. The aluminum stays silver forever and silver forever is the color of something that refuses to age. Refusing to age is not the same as lasting.

The flashing failed at the nail. Every piece of flashing was nailed to the wall and the nail punched a hole in the flashing and the hole was the contradiction. You sealed the gap with a piece of metal and then you punched a hole in the metal to hold it in place. The roofer solved the contradiction by putting the nail under the next piece of flashing so the overlap covered the hole. The overlap was the roofer's answer to his own question. Every good answer creates a new question. The roofer answered them all the way up the wall.

They use peel-and-stick membrane now. A rubber sheet with adhesive on one side that you press onto the joint. No nails. No bending. No copper. The membrane does not turn green because the membrane does not oxidize because the membrane is not metal. The membrane is a product of chemistry. The copper flashing was a product of a man on a roof with a pair of tin snips and an understanding of water. The understanding is the part they cannot put on a roll.

See also: Shingle, Dormer