How to Repair Deck Ledger Flashing

Water is the silent enemy of any deck. When the flashing between your deck ledger board and the house siding fails, it directs moisture directly into your home's rim joist, leading to structural rot that can compromise the entire deck's connection. Repairing this is not just an aesthetic fix; it is a critical structural intervention to ensure your ledger board remains dry and sound. Done well, this repair creates a watertight shingle effect where the house siding overlaps the flashing, which in turn overlaps the ledger board. The secret lies in ensuring that no water can track behind the metal. Take your time with the sealant and ensure the flashing is properly tucked behind your house wrap or building paper, as this prevents water from bypassing your barrier entirely.

  1. Expose the ledger board. Remove the lower few rows of siding directly above the deck ledger. Carefully pry them loose to expose the house wrap and the top of the ledger board.
  2. Check for hidden rot. Check the ledger board and the rim joist of the house for soft or spongy wood. If you can push a screwdriver into the wood easily, you have structural rot that needs professional attention before proceeding.
  3. Prepare the surface. Scrape away old, cracked caulk and debris from the gap between the ledger and the house. Use a wire brush to remove any loose paint or wood fibers to ensure a clean surface for the new flashing.
  4. Slide flashing behind wrap. Measure and cut Z-flashing to the length of your ledger. Slide the top flange behind the house wrap, ensuring it overlaps the top of the ledger board by at least two inches.
  5. Create the watertight seal. Apply a generous bead of high-grade exterior-rated polyurethane sealant along the top edge where the flashing meets the wall. Smooth it out with a damp cloth or finger to ensure a watertight transition.
  6. Close up the wall. Reattach the siding pieces you removed earlier, ensuring they sit slightly above the ledger to allow for expansion and drainage. Replace any damaged nails with new stainless steel siding nails.