How to Install Stairs on a Deck with Lag Bolts

Building a raised deck requires the solid connection of a strong staircase for safely climbing to and from the deck surface. While you could nail the stairs in place through the end joint and into the stair stringers, the best way to create a trouble-free connection that’s unlikely to fail is through the addition of an angle bracket and lag bolts. By using the bracket and bolts, you’ll extend the mounting surface area, by connecting each stringer three times to the surface of the deck and creating a much more secure attachment joint between the staircase and deck surface.

Tape measure
2-by-6 inch plank
Circular saw
Deck nails
Hammer
Stair stringers
Carpenter’s level
Drill
4 1/2-inch framing anchor
1 1/4-inch lag bolts
3-inch wood screws
Lag shields
Stair risers
Stair treads

Instructions

- 1
  Measure the length of the deck on the side that you intend to place the stairs with a tape measure.
- 2
  Cut a 2-by-6 inch plank to the required length with a circular saw. Place the plank onto the posts along the installation edge, with the top of the board against the bottom of the deck joist along the edge. Nail the board into place with three deck nails through the board and into each post. This will extend the length of the joist and give you enough space to set the stair stringers.
- 3
  Place the stair stringers against the side of the deck with the base of the stringers on the poured concrete pad. Check the distance between the stringers at the top and base of the wood to make certain the spacing is the same throughout. Place a carpenter’s level across the stringers to make sure the treads of the stringers are level. Mark the location of the stringers onto the joists on the edge of the deck, including the one you just installed, with a pencil. Remove the staircase.
- 4
  Drill two holes through the joist about 2 inches apart where each of the stair stringers would meet the deck.
- 5
  Return the stringers to the deck. Use the holes through the joist to create pilot holes into the rear of the stringers about 1-inch deep. Drive 3-inch wood screws through the holes in the joists and into the back of the boards with a drill and a screw set.
- 6
  Place 4 1/2-inch framing anchors against the inside edges of the stringers. Mark the mounting holes in the anchors against the stringers and the front of the deck joists. Remove the anchors then drill holes that are 1-inch deep through all of the markings.
- 7
  Replace the anchors then drive 1 1/4-inch lag bolts through the anchors and into the joists and the sides of the stringer.
- 8
  Place anchor bolts along the base of the stringer against the concrete pad. Mark the location on the pad and the stringer with the pencil. Drill 1-inch holes into the stringer with the drill then use a masonry bit to drill the 1-inch holes into the concrete slab.
- 9
  Hammer lag shields into the concrete until they’re flush with the concrete surface. Drive lag bots through the anchors and into the stringers then drive the bolts through the anchors and into the lag shields on the pad.
- 10
  Attach the stair risers and treads after installing the stringers by nailing them onto the stringers to complete the staircase installation.

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