How to Install a Shed Roof Over a Porch
Building a shed-style roof over your existing porch is an easy project that can add some curb appeal, shade and value to your home. A shed roof is a simple design that basically attaches to your house wall on one side, slants down and is supported by a beam and posts on the other end. The span of the shed roof rafters will dictate the size of the boards that you need but any span under ten feet can use a 2-by-6 inch standard construction grade board.
- Place vertical 4-by-4-inch posts over an existing footing that supports the porch floor. Attach each post using steel brackets nailed into the porch floor.
- Cut a strip of 1/2-inch thick plywood the same width as the 2-by-6 inch boards and the same length as the porch. Build a horizontal beam accros the top of the posts by nailing two 2-by-6-inch boards together with the strip of 1/2-inch plywood sandwiched between them.
- Attach the beam to the top of the post using steel brackets that are basically saddles. Be sure to use the manufacturer's recommended steel nails.
- Use a couple of the 2-by-6 boards to temporarily support the posts and beam by temporarily nailing them to the posts. Place them at 45 degrees to the ground and wedge the end into the ground for temporary support..
- Attach a 2-by-6-inch board the length of the roof to the house wall. Locate framing studs on the house to securly attach it. Use construction adhesive to help secure it. Drill 3/8-inch diameter holes through the board and use long 3/8-inch diameter lag bolts to secure the board to the wall.
- Measure and lay out roof rafters by marking the beam and the board on the wall every 16 inches.
- Nail steel joist hangers to the board on the wall using the manufacturer's recommended steel nails.
- Cut the ends of the 2-by-6 inch boards to match the angle of the slanted roof and place one board in each location where you attached the steel joist hangers.
- Place one 12 foot long, 2-by-6 inch rafter in each hanger. Each rafter sits on top of the horizontal beam and extends past it 16 to 24 inches. Nail each rafter in place as you go.
- Nail rafters to the beam by cutting a short 2-by6 inch board to place between each rafter just above the beam. These short are referred to as blocking and prevent the rafters from twisting and also give you something to nail to. Drive nails at an angle into the top of the beam at each location.
- Attach sheets of 1/2-inch plywood on top of the rafters using 8d galvanized nails. Leave a one-inch overhang around the edge.
- Staple felt tar paper over the plywood surface using a staple hammer and 3/8-inch staples. Cut along the edge of the roof evenly using a utility knife,
- Attach aluminum rain drip edging around the roof using roofing tar adhesive and 3/8-inch staples.
- Install matching roofing, making sure to leave 1/2-inch to hang over the edge of the roof. Apply roofing tar adhesive for a secure and weather tight installation. Use 3/4-inch nails to make sure you don't nail through the plywood.
Trim and Painting
- Add trim to the face of the rafters and along the side of the roof to match the existing house trim.
- Apply exterior grade wood primer over all the wood surfaces using a wide brush and roller.
- Apply a coat of exterior grade paint to match the color of your existing house or trim colors to tie the new structure into the old structure.
Things You Will Need
- 12 feet long, 2-by-6-inch boards, (the quantity wil depend on how big your porch is)
- 4-by-8 foot by 1/2-inch plywood
- 2-by-6 inch steel joist hangers
- Joist hanger nails
- 4-by-4 inch posts, 8 feet long
- 4-by-4 inch steel post anchor brackets
- 8d Galvanized nails
- 16d Galvanized nails
- Aluminum roofing rain drip edging
- Roll felt tar paper
- 3/8 inch long staple to attach felt paper
- Roofing material to match existing house
- 3/4 inch long roofing nails
- Construction adhesive
- Use boards a couple of feet longer than the roof span so you can attach a rain gutter later.
- Many ornate details can be added to this structure, such as railings and decorative trim.
- It is very important to insure that you have an adequate foundation to support the weight of the new structure.
- Place the vertical posts in as many locations as needed every 8 to 10 feet along the length of the porch.
- Place posts close to the footer locations that support the porch floor.
- If no footers are used for the porch then posts must be placed into new concrete footings.
- Use wider boards as rafters if the span is over 10 feet.