A do-it-yourself porch roof will not only provide you and your family protection from the elements, but it will also enable you to fully enjoy the use of your porch. If you possess basic carpentry skills, building a porch roof is not a difficult project. The prudent approach to planning your porch roof is to blend the roof in with the style and materials used on the roof section located above the porch.
Conduct a through inspection of the existing structure. Start with the wall where the roof will be attached to the house. Also, examine the current porch support beams and the concrete piers. Damaged components must be properly repaired to ensure that the additional weight of the new roof will have the required support.
Find out what the building codes are for porch-roof construction. Many building departments have specifications regarding the minimum allowable slope for roofs as well as approved methods for attaching the ledger board to the house framing. Comply with the minimum building code requirements, or even exceed them. You'll likely need to get a building permit before you can start your DIY porch-roof project. Usually, a building inspector must give final approval once the work is complete.
Constructing the Roof
Follow the local building code for the correct method of securing the ledger board to the house framing. The ledger board is the horizontal plank, which must be constructed of at least 2-by-6 board, that serves as the plate for attaching the roof rafters. Keep in mind, the ledger board must be positioned slightly higher than the roof support beam to account for the slope of the roof.
Use pressure-treated lumber and make sure that is straight. The ledger board must be plumb and level to ensure the proper alignment of the roof. Make the joint between the roof and the house watertight by installing Z-flashing.
Typically, employ 4-by-4 pressure-treated lumber for the posts, which will support the roof. Secure the posts in the ground with a quick-setting concrete. Make the diameter of the concrete at least 12 inches. Use a carpenter's level to check the posts' alignment. Support the post with 2-by-4s until the concrete hardens.
Strengthen the roof's structure by placing the 2-by-6 rafters 16 inches on centre. Build the support beam, which rests on the posts, out of two 2-by-6 boards. Make the beam even stronger by putting a piece of ¾-inch plywood between the two boards. When you fasten the rafters on top of the beam, use rust and corrosion-resistant galvanised nails or stainless-steel fasteners. Use the same type of fasteners to secure the other framing members.
Sheath the roof structure with 5/8-inch plywood or OSB (Oriented Strand Board). Cover the roof with the same material used on the house roof.