To prevent water from penetrating behind the top edge of base flashing, a separate piece of flashing should be provided over the top. This flashing is known as “counter flashing” and is usually made of sheet metal (see Figure 119).
Note : Counter flashing is also required to protect the base flashing from impact and UV radiation damage. This is necessary if the base flashing is a built-up bituminous roofing membrane or made of any material that deteriorates in sunlight. Counter flashings should be installed so that they are easily removed to allow for inspection of the flexible base flashing below.