How to Attach a Roof Deck to a House

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Roof decks require secure points of attachment to a house to survive strong winds, earthquakes and the tramping feet of guests for parties or fireworks displays. Whereas standard decks rely on a ledger board attached to the house foundation and posts for support, roof decks instead involve sturdy beams on 2-by-6 boards called sill plates. The complexities of creating a safe roof deck often lead permits departments to require that an engineer or architect design and stamp your plans to verify the deck will be a solid, sturdy structure.

Things You'll Need

  • Tape measure
  • 2-by-6 pressure-treated lumber
  • Spirit level
  • Scrap wood
  • 2-by-10 or 2-by12 pressure-treated lumber
  • Chop saw
  • Galvanized lag bolts, washers and nuts
  • Hold-down brackets
  • Drill and bit set for masonry and wood
  • 3/8-inch threaded rod
  • High-strength epoxy
  • Mark the planned location of sill plates on the roof per the architectural drawings. You may need to carefully measure the distance from roof features such as ridge lines, chimneys, vent stacks, skylights or party walls of adjoining row houses, in accordance with the plans, to arrive at the sill plate locations. Expect to mark four sill plates -- two each for the front and rear beams of a simple rectangular deck -- and six sill plates for a larger or multilevel roof deck.

  • Cut a 12-inch length of 2-by-6 pressure-treated lumber to make each sill plate. Place it on its designated spot. If the roof is not level, cut shims from scrap wood to bring the sill plates horizontal and confirm with a spirit level.

  • Create beams out of doubled -- or sometimes tripled -- 2-by-10 pressure-treated lumber bolted together with galvanized lag bolts, following your approved design plan; the plan could also call for even larger 2-by-12s to create a beam for wider spans. Center the front beam on the front pair of sill plates and the back beam on the back plates, having an assistant hold each beam in turn vertically and plumb with the spirit level.

  • Press two large angle brackets, called hold-down brackets, on each sill plate on either side of the beam. Drill with a 3/8-inch wood drill bit through the sill plate and shim. Switch to a masonry bit as you continue to drill, if you are attaching the sill plate to a brick party wall, placed in the chuck of a hammer drill. Follow the architect’s instructions, which may call for inserting into the hole a 3/8-inch threaded rod acting as an anchor, embedded in quick-setting epoxy, to affix the sill plates and hold-downs.

  • Top the anchor rod with a galvanized washer and nut to secure the hold-down bracket to the sill plate and the sill plate to the roof itself. Drill with a wood bit through the holes at the top of the hold-down brackets on either side of the beam and through the beam itself, sandwiched between the brackets. Push a galvanized lag bolt through the brackets and beam, and tighten a washer and nut with a socket wrench.

  • Complete the deck by installing joists atop the beams, covered with deck boards and with corner posts on the perimeter to support a top and bottom rail and your balusters, as you would a deck at ground level.

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