Deck Flashing Installation

Deck flashing is a critical component of any outdoor deck that is attached to a house or other permanent structure. It prevents water from collecting around the ledger board, which supports nearly half the weight of the deck. It also keeps moisture from entering the space between the deck and the foundation of the house. Without proper flashing, water can damage both your deck and your home, and can even contribute to deck collapse.

Types of Flashing

Choose the best type of flashing for your particular deck project and budget. Aluminum flashing is common, but it can contribute to corrosion of nails and other surfaces. Copper is more expensive, but it resists corrosion. You can also purchase waterproof membranes that adhere to the exterior wall and ledger board surface. These membranes are easier to manipulate than aluminum or copper and they resist deterioration.

Aluminum or Vinyl Siding

Remove the aluminum or vinyl siding up to 6 inches above the top edge of your ledger board before installing flashing. Slide the flashing up at least 3 inches behind the siding. Replace the siding before completing the deck. Leave enough flashing that you can bend it over the top of the ledger board, and bend the edge over the front of the ledger board.


Remove the stucco up to 6 inches above the top of the ledger board. Also, remove the backing that was installed between the wire mesh and the stucco. Slide the flashing up at least 3 inches under the wire mesh. If the nails holding the mesh to the structure are in the way, remove them with a hand-held reciprocating saw or a hacksaw. Bend the lower end of the flashing over the ledger board.

Installing Flashing for an Existing Deck

Pull up the three or four deck boards closest to the structure. Install the flashing in the same manner as with a new deck. Add a joist to act as a nailer for the deck boards you pulled up. Place the deck boards back into position and refasten them.

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