How to Add a Carport to a Garage
Adding a carport to your garage can multiply your dry storage space and give you a covered place to keep boats, recreational vehicles and second or third cars out of the weather. You and several partners can attach a simple wood framed carport to the side of an existing garage in a weekend. Use only pressure treated lumber.
Building Attached Carport
The side of your garage must be tall enough to allow 8 feet of clearance in your carport. Locate the 2-by-8 header on the side of your garage by measuring 8 feet up from the ground at each end of the garage. Measure 1/2 inch in from the back edge of the building and mark the spot. Lift the header so the wall marks are at the header bottom; make sure it is level end-to-end. Fasten the header to the garage wall studs with the lag screws.
Lay out your carport by dropping a plumb line from each end of the header. Mark the spots where the plumb bob touches the ground. From each marked spot, attach a string to the building and measure 15 feet out. Make sure each string is perpendicular to the garage wall. On each side, drive in a stake at the 15 foot mark and tie the string to it. Then, tie a string between the two stakes. Make sure the distance between the plumb marks at the garage wall and the outer stakes is identical. Measure the diagonals from one plumb line mark to the opposite corner stake. If the measurements are identical, the layout is square to the building.
Dig a hole 2 feet deep where one of the corner stakes is located. Set in one of the poles. Check for correct distance from the wall and the opposite corner stake. Use your level to make the pole plumb. Brace it in place with 2-by-4 boards. Repeat to set a pole at the opposite corner. Repeat for two additional support poles, each spaced a third of the distance between the corner posts. Mix concrete and pour it into each pole hole. Once the concrete sets, mark 7 feet from the ground on the outside of each end pole. Lay one end of a 2-by-6 against the end of the header and the other end above the mark on the corner post. Mark the angle at the header end.
For a front support beam, fasten 2-by-6 joists to each side of the row of poles, with their tops level and at the 7 foot mark. If using 16 foot joists, cut header ends at the correct angle for a tight fit and cut the opposite ends at the same angle. Fasten joist hangers to the wall header, set 24 inches apart. Fasten joists to the hangers and to the front support beam with joist beam braces. Cut post tops level with the joists. Attach 2-by-4 braces at a 45 degree angle at each corner and each post. Nail 2-by-4 studs, spaced 18 inches apart, across the joists to support the metal roofing. Fasten sheets of metal roofing to the roofing supports. Fasten the 1-by-6 fascia board to the joist ends. Spread gravel over the carport floor.