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How to Flash a Ledger Board for a Pergola

Tim Anderson

Pergolas are projecting eaves which are normally reserved for garden areas or where you want to link a building to an open garden area or a pool. They are generally not solid roofs, but are instead simply rows of horizontal joist-like beams that run across, often times with hanging vegetation or plants providing shade for people passing below. They are attached to ledger boards along the eaves of a house, just like deck planks are attached to a ledger board for decks. And, just like decks, the ledger board needs to be flashed so water dripping from the roof doesn’t penetrate to the wall of the home.

Pergolas offer shade along the edge of a building.

Step 1

Loosen any siding that is in place along the wall above the ledger board, if necessary. Use the claw of the hammer to loosen nails, or the drill to reverse any screws holding the siding in place. Gently pry the siding element loose along the top of the ledger board across its entire length.

Step 2

Squeeze silicone adhesive onto the top edge of the ledger board along its length. Also apply silicone caulking to the vertical portion of the wall along the top of the ledger board down the entire length. Slide the Z-flashing into place so that it slides up under the siding and across the top of the ledger board in the bead of silicone, with its remaining vertical section hanging down over the face of the ledger board.

Step 3

Reattach the siding on top of the ledger board, locking the Z-flashing in place. Install your pergola sections as you would normally, attaching them to the ledger board and running across your area. For best results, wait until the silicone adhesive has dried before you install your pergolas.