How to Install Step Flashing Under Siding

Step flashing is a unique type that is designed to work with siding and other types of exterior paneling and construction methods. It has a step system where the flashing is designed to be installed along inside corners, where the L-shaped flashing can be slotted under the two finish materials. For siding, it is ideal for along the upper section of the wall where it meets the eaves, as well as any other inside corners that need to be covered and protected. It goes under the waterproofing layer for the siding, with the siding covering both layers.

Vinyl step flashing
Silicone adhesive
Utility knife
Caulking gun
Tin snips

Instructions

- 1
  Install the flashing directly on top of the plywood layer that serves as the base for the siding. Use a vinyl type of flashing that can be installed with adhesive, rather than a metal type that needs to be nailed in place. Nailed flashing can lead to eventual leaks due to the fact that a nail is penetrating the plywood.
- 2
  Cut the tip off of a tube of silicone adhesive so that you have at least a 1/4-inch opening in the top and insert the tube into a caulking gun. Pull the trigger to dispense the caulking and run a bead along the backside of the L-shaped step flashing. Press the flashing into any inside corners that need to be protected and waterproofed. Cover the seams between pieces with more silicone.
- 3
  Cover the flashing as well as the rest of the wall with whatever waterproofing is recommended by your siding manufacturer, which varies by the manufacturer and the type of siding you are using. Install the siding on top of that waterproofing layer to completely cover the waterproofing and the flashing beneath, leaving behind a finished surface.

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