How to Add a Carport to an Existing Wall

Written by dan aragon
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Adding a carport to the side of your existing house is a job that a beginning do-it-yourselfer can do. A carport will protect your car from harsh weather, provide a shading spot for an outdoor lunch and may even increase the value of your home.

Skill level:

Things you need

  • Three 4-inch square posts
  • Steel mounting brackets
  • Three 4-by-4 pressure-treated posts, 8 feet long
  • Twenty, 2-by-6 boards 10 feet long
  • Forty, Steel Joist Hanger
  • Six, 2-by-4 boards, 10 feet long
  • Ten sheet of 1/2 thick Plywood sheets 4 foot by 8 foot
  • Staples
  • Galvanised nails, 8 penny and 16 penny
  • Three steel saddle brackets to attach beam to posts
  • Six 80-pound bags of Ready Mix concrete

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    Layout and site preparation

  1. 1

    Determine the location of your carport against an existing house or garage wall that best suits your needs for convenience and functionality.

  2. 2

    Measure and mark three locations for foundation footings 10 feet away from the existing wall. The entire structure in this design will be 10 feet by 20 feet long.

  3. 3

    Measure and mark the location of the ledger board that will be mounted to the existing wall. A ledger board is simply a 2-by-6 board that will be bolted to the existing wall using 3 1/2-inch lag bolts and will have the joist hangers attached to it.


  1. 1

    Dig three holes at least 36 inches deep by 12 inches in diameter at the predetermined locations for the foundation footings.

  2. 2

    Fill each hole with wet concrete mix all the way to the top of the hole.

  3. 3

    Place the three steel post mounting brackets into the wet concrete before it dries. This will allow you to manipulate the position and height of each post mounting bracket. Use a line level and nylon string to make sure all brackets are exactly 10 feet from the existing wall and are at the same level.

  4. 4

    Allow the concrete to dry overnight before starting construction.


  1. 1

    Add an 8-foot 4-by-4 post to each footing by nailing them into the steel mounting brackets. Use a couple of long 2-by-4 boards to hold each post in place in a plumb position.

  2. 2

    Build a horizontal support beam across the top of all of the three posts by nailing and gluing two 2-by-6 boards together with a trimmed piece of 1/2-inch-thick plywood between them. The thickness of the two boards and the plywood will equal 31/2 inches to match the posts (actual measurement of a 4-by-4).

  3. 3

    Mount the horizontal beam on top of the posts and securely attach each post with a steel mounting bracket called a saddle.

  4. 4

    Attach a single layer 2-by-6 board to the existing wall that matches the length of the horizontal beam previously built. Use 3-inch by 3/8" diameter lag bolts and construction adhesive to attach the ledger board to the existing wall. Use a stud finder to locate the vertical studs on the existing wall. Drill holes through the ledger board at each location where there is a vertical stud. This is usually going to be every 16 or 24 inches. This step is very important.

  5. 5

    Measure and mark locations on the horizontal beam and the ledger board to mount joist hangers every 16 inches on centre for the entire length of each.

  6. 6

    Measure the distance from the joist hangers on the existing wall out to the joist hangers on the horizontal beam.

  7. 7

    Measure and cut enough 2-by-6 boards to fill each location of joist hangers. There should be a slight roof slope so the ends of each of the roof rafters should be cut at the matching angle to fit properly into the joist hanger.

  8. 8

    Nail a roof rafter 2-by-6 board into place using the manufacturer's recommended nails.


  1. 1

    Nail 1/2-inch plywood sheets to the top of the roof rafters. Trim the 4-foot-by-8-foot sheets of plywood to fit the entire roof area but make sure to leave a 1-inch length of plywood that protrudes past the edge of the end rafters and the horizontal beam.

  2. 2

    Staple 30 pound felt paper to the top of the plywood rood surface using 3/8-inch staples by starting at the edge of the roof and work your way back to the existing wall by overlapping rows about two inches. Nail aluminim rain drip edging around the perimeter of the roof to hold down all of the edges of the felt paper.

  3. 3

    Apply roofing material of your choice over the felt paper to match the existing house or garage roof.

  4. 4

    Apply a coat of primer and paint to the entire structure to match the colour of the house.

Tips and warnings

  • Make sure that the vertical support posts are aligned and level to each other.
  • If your property slopes, the height of each post must compensate for the slope.

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