How-to-install-flashing-before-siding, jonathan discusses the need for flashing over stone.. How to install step flashing under siding. keep water out of your home and running down the roof where it belongs with appropriate use of step flashing. step flashing is used where a roof meets a ..., are drip metal screeds needed for brick, stone, or block walls - duration: 2:48. kirk giordano plastering inc. 17,825 views. When installing new vinyl siding, window trim, also called j-channel, must be installed before hanging siding panels. although j-channel trim pieces are designed to prevent rain water from getting behind siding panels, for extra protection against water damage, you should seal the perimeter of each window with flashing tape before installing trim pieces.