How to Add on to an Existing Porch or Deck

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As your needs change or your family grows, you may need to adjust the size of your porch or deck. The extension that you add to a current outdoor structure should be at the same level or have steps leading down to a lower level. Creating an extension to a porch or deck is similar to creating and installing a new structure. Before you begin your project, check with you city planning office to see if you need a building permit. Then contact your utility providers to learn if there are underground pipes or lines.

Things You'll Need

  • Saw
  • Tape measure
  • 2-by-6 lumber, cut to size
  • Nail gun
  • Nails
  • Level
  • Drill
  • Drill bit
  • 3/8-inch lag screw
  • Stakes
  • Masonry string
  • Laser level
  • Posthole digger
  • Gravel
  • 4-by-4 lumber for the posts, cut to size
  • Concrete
  • 2-by-8 lumber
  • 7-inch carriage bolts with a 3/8-inch diameter
  • 2 inch-by-6 inch joist hangers
  • 2.5-inch deck screws
  • 5/4-inch decking boards
  • Draw a scale image of your current deck or porch, followed by a sketch of how you want the structure to look with the addition. Planning the structure can help save you time and purchase the correct amount of materials. As you map out the new deck or porch, decide if you want to keep or remove the existing rails, add benches and keep any existing stairs.

  • Remove old railings and stairs that you no longer want on the existing deck, as well as plants, trees and bushes that are in the way.

  • Create ledger boards out of lengths of 2-by-6 lumber. Use nails to temporarily attach the lumber along the edges of the deck or porch, as if it was molding. As you attach the lumber, make sure it is level.

  • Create pilot holes along the midline of the ledger boards. Space the holes by 3 inches and place a 3/8-inch lag screw in each hole to permanently secure the ledger boards to the existing structure.

  • Use stakes to help you outline the perimeter of the deck or porch addition. Then tie masonry string around the stakes at the height that you want the extension. Use a laser level to help you place the masonry string at the correct height.

  • Dig holes that are 2 feet deep for the posts using a posthole digger.

  • Prepare concrete according to the manufacturer’s instructions.

  • Place 2 inches of gravel at the bottom of each hole that you dug, followed by posts cut from 4-by-4 lumber. Back fill each hole with the prepared concrete. Allow the concrete to cure. You may need to use supports to keep the posts upright as the concrete dries.

  • Secure 2-by-8 lengths of lumber to the posts to begin creating a beam system. Secure the lumber to the posts with 7-inch carriage bolts that have a 3/8-inch diameter.

  • Place 2 inch-by-6 inch joist hangers along the inside perimeter of the deck or porch, spacing them on center by 16 inches. Secure the joist hangers to the lumber with 2.5-inch deck screws.

  • Slip 2-by-8 lengths of lumber into the joist hangers and secure them together with deck screws. These lengths of lumber will help support the deck or patio floor.

  • Install the floor of the deck or porch. Arrange planks of 5/4-inch decking boards in any manner that you like and drill pilot holes into the ends of the planks. Secure the planks to the supporting lumber using deck screws. When you install the floor, butt the deck boards together.

Tips & Warnings

  • If the porch or deck is more than 6 inches off the ground, consider installing railing and steps to help increase the safety of the structure.
  • Photo Credit Ryan McVay/Photodisc/Getty Images
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