How to Extend a Deck

Extend your deck rather than replace it to create the outdoor entertainment space of your dreams.

wooden deck in backyard of modern house

John Granen

Project Overview
  • Working Time: 12 hours
  • Total Time: 2 days
  • Skill Level: Advanced
  • Estimated Cost: $300 to $800

Short on space for outdoor entertainment? Put the demolition tools away, because there's no reason to tear out a deck simply because it's too small. Instead, consider extending your existing deck to create more room. Let's face it, things can get a little tight once you add a grill, an outdoor dining table, and a chair or two. Luckily, extending your deck is a relatively simple process.

With the right tools, a helping hand, and our step-by-step deck extension tutorial, you can increase the size of your deck over the weekend.

Before You Begin

There are a couple of things to consider before getting started on your DIY deck extension.

  1. Reference your local building codes or HOA rules and guidelines before making any outdoor additions. The last thing you want is to spend money and time on a project that will have to be undone.
  2. Inspect your existing deck's materials for structural integrity. If there's any doubt that the materials are in good enough shape to support the new components, you're better off getting a second opinion from a contractor before moving forward. They will be able to inspect and replace any compromised materials.

Deck boards that look bad on the surface aren't indicative of structural damage. In many cases, the damage is purely cosmetic and can be solved by resurfacing and refinishing the entire deck once the deck extension is complete.

What You'll Need

Equipment / Tools

  • Measuring tape
  • Circular saw
  • Hammer drill
  • Drill
  • Drill bits
  • Hammer
  • Post-hole diggers
  • Shovel
  • Wheelbarrow
  • 4' level


  • 2x6 pressure-treated joists
  • 2x12 pressure-treated beam
  • 4x4 ground-contact posts
  • joist hangers
  • gravel (optional)
  • quick-setting concrete
  • 3" exterior wood screws
  • 3-1/2" concrete lag bolts with matching masonry bit
  • Scrap boards
  • 5/4" pressure-treated deck boards
  • Water-diverting flashing (optional)


How to Extend a Deck

  1. Remove Railing

    Remove the railing, balusters, and any exterior trim that might get in the way of the deck extension. If your deck boards are damaged or you plan to replace any deck boards, remove them along with any nails or screws.

  2. Measure and Mark the Building

    Most decks are attached to a house or other structure, so, if you plan to increase the width along the structure, measure the distance you wish to expand the deck and check to make sure there is solid material to fasten a ledger board to, as well as no obstacles like water spigots, windows, and drain pipes. Mark the measurement on the wall with a pencil.

  3. Cut and Attach Ledger

    Cut the ledger board to the length, then enlist a helper to assist you in holding it in place. Place a 4-foot level on top of the ledger to ensure it is sitting perfectly level, then drill through the board and into the wall using a masonry bit and a hammer drill, as the wall is likely cinderblock or concrete. Fasten the ledger to the wall using concrete lag bolts.

    If attaching your ledger board requires you to remove siding, flash the top of the ledger using water-diverting flashing before reinstalling siding. This will prevent water from running behind the ledger directly into your wall.

  4. Measure and Cut End Joists

    Cut your end joists to the proper length to extend the length of your deck. The end joist attached to the end of your new ledger will be the full length of the deck, while the end joist on the opposite side will be the full length of the deck minus the length of the existing structure.

  5. Attach End Joists

    Attach the longer end joist at the end of the new ledger using wood screws to toenail the board. Place a scrap support board with its end resting on the ground at the free end of the joist. Place a level on top of the joist, adjust the joist until it's level, then screw it into the scrap board temporarily. Repeat this process on the other side using the shorter board.

    To make it easier to install the posts later on, position your temporary supports back 1 to 2 feet from the ends of the board.

  6. Cut and Attach Band Joist

    Measure and cut the band joist to the full width of the deck, using the existing deck and the new ledger board as your reference point. Hold the band joist up against each end joist and screw through the band joist into the end joists.

  7. Check for Square

    Check the frame for square by placing a large framing square in each corner. Adjust the frame as needed by scooting the temporary supports with a hammer.

  8. Measure and Cut Corner Posts

    Cut the corner posts to length. Find this length by combining the height of the railing, the measurement from the top of the deck to the ground, as well as your local building code's requirements for the amount of the post that should be underground. Remember, you can always cut more off afterward if you leave a little excess.

  9. Bury and Attach the Posts

    Check your local building codes for deck-post hole requirements. They will specify the necessary depth of the hole, as well as if you should use gravel, cement, or both. Dig and set the posts in each corner following these requirements, placing the posts on the inside of each corner.

    Once the posts are in the ground, screw through the outer joists into each post.

  10. Cut and Attach Beam

    Cut a 2x12 beam to the length of the band joist and screw it to the inside of the posts, pressed against the bottom edges of the end joists. Depending on your deck extension size and your local codes, you may need additional posts and beams to support the weight of the deck.

  11. Cut and Attach Joists

    Cut and attach your inner joists using your local building codes to determine your joist centers. Typically, joists will be positioned every 16 inches. Screw through the band joists into the ends of the joists, then attach the other end using joist hangers on the ledger.

  12. Replace Deck Boards, Balusters, and Rails

    Replace the deck boards, balusters, and rails once the frame is complete.

  13. Seal the Wood

    Seal new wood using your preferred deck sealer. For best results, sand and refinish the existing deck boards.

Related Articles