Building a roof on a shed or anything for that matter can be a little complicated in both planning and building. I am going to explain how to build a gable roof which is what you see on houses, it’s basically a roof that slopes on both sides with a peak in the middle. Before you begin you need to check your local code for the slope of the roof. A common slope for a shed is a 5-in-12 slope, which means the roof rises 5 inches for every 12 inches of distance. This is what I will explain how to do.
First you need to brace a temporary ridge pole at the center of the cap place on an end wall and then mark the roof’s total rise on the ridge pole. To calculate the total rise you need to multiply half the length of the end wall by 5 for a 5-in-12 slope. For a 5-in-12 slope on an 8×10 foot shed, you would mark 20 inches above the cap plate. Next, lay out one 2×6 rafter by snapping a chalk line along the center of the board, then align the chalked line with the corner of the cap plate and the mark on the ridge pole. Once you have the board in position attach it in place. You are just tacking it on right now, this is not the permanent attachment.
Next, mark a plumb ridge cut on the rafter at the center of the ridge pole. Measure 13 inches from the cap plate on the rafter to mark a plumb overhang cut. Trace the cap plate onto the rafter to lay out a notch, this is called a bird’s mouth cut. make the cuts, then use the rafter as a template to lay out the others. Cut a 1×8 ridge beam 1 foot longer than the shed for a 6 inch overhang at each end. Begin by assembling braces with 1×6’s and 2×2’s at the center of the end walls to hold the beam in position at its final height. Lay out rafters on the beam 6 inches from each end and every 24 inches on center. Next you need to mark the rafter locations on the cap plates at each end and every 24 inches on center. Position each rafter against the ridge beam with the bird’s mouth cut sitting on the cap plate. Toenail the rafter to the ridge beam and cap plate with 8d (2-1/2 inch) common nails.
You need bracing in this process as well and that comes with collar ties, these are simply braces that help support the roof. Collar ties are made of 2×6’s that run parallel to the rafters. Cut one 2×6 to length and set it on the cap plates against the rafters, then trace the slope of the rafters onto it. make the cuts then use the collar tie as a template to lay out the others. Nail the collar ties to the rafters with 10d (3 inch) common nails. Cut 2×4 blocking to fill the space left on the cap plates along the eaves and nail it in place with 8d nails. Next, cut four rafters without bird’s mouths and cut two 1×8 fascias the same length as the ridge beam. Set each fascia just below the top of the rafters so sheathing will clear it and align it with the beam using a rafter. nail the rafter to the beam, then nail the fascias in place with 6d (2 inch) nails.
Cut 2×6 blocking to fit between the outer rafters at each end of the roof. Position the blocking and drive 10d common nails through the rafters into it. Install 2×4 cripple studs on the cap place of each end wall to support the roof . These cripple studs are just a stud that goes from the top plate to the rafter with a notch cut out and an angle to fit inside the roof. Lay out the notch in a stud by holding it in place and tracing along the rafter. make the cuts, then nail the stud to the rafter and the cap plate. Finally frame an opening for a gable vent between cripple studs at each end of the roof with 2×4’s. Make the opening slightly larger than the vent to be sure it will fit. A gable vent might be a little much for a shed because, well, it’s a shed. You can do this if you want but it is not necessary.
That should do it for the design and assembly for a gable roof. On paper it sounds easy but it really is complicated and time consuming. It took me a lot of roof building before I got it down. There are lots of different styles and techniques, I hope this helps you find yours. Once you have planned it out and have it laid out it gets easier but just take your time and take it one step at a time. Good luck.
