How to Attach a Ledger Board to Flagstone

Many local building codes require attaching decks directly to the home with a ledger board. The ledger board attaches to the home, and the edge of the deck secures to the top of the ledger board, eliminating the need for posts against the house. Attaching a ledger board requires a level surface. Mounting to a flagstone foundation presents a problem because the flagstone is often uneven. The best way to attach a ledger board to flagstone is by attaching a 1-inch-thick board to the flagstone first. The board secures directly to the uneven flagstone and provides the level surface necessary for the ledger board.

Tape measure
Helper
Chalk line
3/8-inch masonry bit
Hammer drill
Compressed air
1-inch-by-6-inch board (as long as your ledger board)
Circular saw
Drill
3/4-inch paddle bit
1/2-inch drill bit
Socket wrench
3/8-inch wedge anchors
3-inch wood lag bolts

Instructions

- 1
  Measure the height necessary for the top of the ledger board onto the flagstone foundation in two places. Ask your helper to hold one end of the chalk line as you stretch the line across the foundation wall at your marks. Snap the chalk line to make a chalk mark across the foundation.
- 2
  Move the chalk line down 4 inches and snap another line. This second line is the height your mounting anchors will install.
- 3
  Starting at one end of the second line, mark mounting holes every 16-inches with a pencil down the length of the foundation wall where you want the ledger board. Ensure that your mounting hole marks go onto flagstone and not mortar. If necessary, move marks closer together than 16 inches.
- 4
  Drill mounting holes at your marks with a 3/8-inch masonry bit and a hammer drill. The holes should be 1 inch deep. Blow out each hole with compressed air to remove flagstone and concrete dust.
- 5
  Cut a 1-inch-by-6-inch board to the same length as your ledger board with a circular saw. Mark the mounting holes onto the board with a pencil. Drill into the marks with a 3/4-inch paddle bit and a drill. Only drill 1/4 inch into the wood. Change the paddle bit to a 1/2-inch drill bit and drill through the board.
- 6
  Insert 3/8-inch wedge anchors into the mounting holes in the flagstone foundation. Hold the 1-inch-by-6-inch board in place with the assistance of your helper. Secure the board to the foundation by driving 3-inch wood lag bolts into the board and anchors with a socket wrench.
- 7
  Place your ledger board against the first board. Drive 3-inch wood lag bolts through the ledger board and the first board.

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