How to Build a Roof for a Shed
A simple lean-to style roof can be built on top of a shed with 2 x 6 roof rafters, a plywood deck and rolled asphalt roofing as the roof material. With this type of roof construction, the builder will learn how to use a framing square to make an elementary cut in the roof rafter. This cut or notch needs to be made in two places on each rafter so that the timber will fit snugly on top of the two wall plates. When finished, you will have a simple lean-to style roof on top of your shed that directs all forms of precipitation off the rear end toward the ground.
Cut the rafters to length. You will want the rafters to overhang at both the back and the front of the building, so you need to add a foot at each end. This means that if the building is 10 feet wide you will want to use a 12-foot-long 2 x 6 for your rafter.
This is only part of the process, for your cut will not be a square one. To make the correct cut, you need to calculate the rise over run. This is very easy. You know the run already, for that is the width of the building, 10 feet. The rise is simply the difference in height between the front and back of the building. For instance, if the building is 10 feet high in front and 8 feet high in back, then the rise is 2 feet. So now our rise over run is 2 to 10, which can be reduced to 1 to 5. This is an important ratio that we will use when cutting the ends of the rafters as well as the notches that go over the two plates.
To cut the end, you need to mark a line with the framing rafter. To do this, lay the board out on your sawhorses and place the rafter over your board so that the corner of the square goes way past the edge of the board. Adjust the square until you get the 1 to 5 ratio in the notch of the framing square. The 1-inch distance will be toward the outside edge of the board and the 5-inch length will be toward the center of the board. Now make your mark on the board. This is your angle for your front cut. You can leave the rear part of the rafter square. You can cut all the rafters in this manner at this time. Make sure the length is the same for all.
Take one rafter and set it in place above the two plates. Line it up so that the ends overhang at both the front and back of the building. Now mark the two points of contact on the rafter and then draw an arrow indicating where the the front edge of the plate will meet the rafter after it has been cut.
Next, take your board down and lay it on a pair of sawhorses with the marks facing up. Now place your square on the board so that the outside corner lies between one set of marks. Adjust the square until you get the 1 to 5 ratio, while keeping the square in contact with the two marks. When one side of the square reads 1 inch and the other side reads 5 inches, you can make your mark, but remember the 1-inch measurement goes toward the rear of the building.
Now do the same for the other pair of marks.
Cut the notches in the rafter with a hand saw.
Put the rafter in place to see if it fits. If the rafter fits, then use it as a template to cut all remaining rafters. Make sure they are identical.
Toenail each rafter to both top plates using two framing nails at each plate. They can be either 16 or 24 inches on center.
Cut blocks to put between each rafter. Do this above each plate for the entire length of the building. This helps seal the building.
Complete the side walls of the building. It is good to wait until this point to build the side walls. Use braces to hold the front and back walls in place before this task is done.
Cover the roof with exterior grade plywood. Run the plywood at a right angle to the rafters and stagger all seams. It is a good idea to extend the plywood a few inches past the roof frame in all four directions.
Nail a drip edge to four edges of the roof. Use galvanized roofing nails to do this.
Cover the roof surface with heavy-duty felt paper. Nail or tack the paper down lightly. Start at the bottom edge and work your way up the roof.
Cover the felt paper with asphalt rolled roofing. Use roofing nails and roof cement to seal the edges and seams.
Things You Will Need
- Framing square 2 x 6's Framing nails (16 galvanized common nails) Exterior grade plywood Galvanized roofing nails Heavy weight felt paper Rolled roofing Saw horses Circular saw Crosscut hand saw Drip edge Roofing cement
- Make sure the front and back walls are plumb before you begin.
- Be careful once you start working on top of the roof. If you can apply the first row of plywood from a ladder or scaffold, then do so.