How to Add a Roof Line to Cover a New Porch

Locate a connection point on the house wall or roof. Identify joists, wall plates, studs, rafters or trusses capable of supporting the new roof line. Outline the new roof line connection, on the house wall or roof with chalk or by sketching on graph paper. Mark horizontal lines to attach a shed roof, a triangle for a gable roof with slopes to the pitch of the porch rafters or trusses.

Use prefabricated trusses to frame any new roof line; they are stronger and easier to install than individual rafters for any style of roof line. Angle a shed roof from the house to the outside edge of the porch. Run gable angles perpendicular to the house, with slopes on either side of a center peak. Remove shingles or siding from the wall or roof where the new line will connect to attach the new line.

Install ledger boards on the house wall or roof to support the addition. Use 2-by-6-inch boards fastened to house framing with lag bolts, horizontal ledgers for single-slope roofs or triangular ones for gable roofs. Adapt the connection method to the house; gable trusses on a vertical wall, for instance, can be fastened directly to the framing but require angled ledgers and connecting diagonal rafters between the first truss and the roof for attachment to a sloped roof.

Mark truss locations on wall caps or ledgers with a tape measure, spaced 24 inches apart the length or width of the roof, depending on the style of the addition. Fasten single-slope rafters to the ledger and to the outside porch frame with metal rafter hangers, installed with 8d galvanized nails and a hammer. Install gable trusses by setting them upright on the porch walls and nailing the truss ends to the wall caps with 16d framing nails.