Adding a gable roof to your existing roof is a great way to increase the value of your home and proves to be a cost-efficient project when you do it yourself. With some guidance and a few helpful tips, your new addition can be a success.
Where to Begin
First, you need a blueprint of your project. If your City Inspector approves, you may be allowed to hand draw your projected plan on paper, but you must include dimensions, pitch, and materials you will be using to complete the job. With any construction job, you must first obtain a permit before beginning work. Next, you need to write out a list of materials you'll be getting from the building supply.
Plumb Existing Structure, Add Cap Plate, and Metal Fasteners
Using a plumb bob, a bubble level, and a carpenters square, check your existing wall and roofline to make sure it is square and level. Then, nail 2 x 4's around the perimeter of roof area you will be adding a new structure to. This is called the Cap Plate. On the cap plate measure and mark off where the trusses will line up. The trusses need to be spaced 24 in. apart. On those marks, nail metal fasteners down so the trusses can be nailed to them.
Getting the Trusses on the Roof and Secured in Place
You need at least two helpers, (four is better) to hoist the trusses on the roof.
Beginning with only one Truss, holding it in the upside-down position, raise up to the roof. Once it is up, flips the top side up. Nail boards on any two vertical boards, angling them to meet the ground. This will strengthen it while it holds the weight of many trusses temporarily. Now, hammer two stakes into the ground. On the two stakes at the end, drill a hole in each of them. Also, likewise, drill a hole into the ends of the boards extending from the truss to the ground. Insert a bolt into each of the two boards and attach them to the two stakes. Finally, nail off the truss to the metal fasteners on the Cap Plate. Hoist up a few more trusses and lean them against the first one.
Adjoining and Placing Trusses and Prepare Rafter Tails
Using 2 x 4's, measure 24 inches plus an additional 6 in. for overhang, and 1 1/2 inches for the sub-fascia board. Nail it near the peak of the trusses. Continue to measure 2 x 4's to allow nailing at each truss until you reach the end of your roof and add the additional 6 inches and 1 1/2 inches for that end. Next, cut out slots in rafters so a 2 x 4 will sit flush with it on the Cap Plate. Finally cut slots in the underside of each rafter flush against the wall with a saws-all. This cut will be 1 1/2 inches deep to slide 2 x 4's in each slot. Nail up sheathing to the walls in a staggered pattern and nail down the decking to the roof. Finally to keep it dry, nail down roll roofing over the decking.
This completes the construction of your gable roof. You can now paint and add a composition or metal roof over your new addition. I hope this sheds some light on adding on a Gable roof to your existing structure.