Things You'll Need
Aluminum drip edge
1¼-inch galvanized roofing nails
Ice and water shield
Electric staple gun
Flat roofs may seem a lot easier to apply roofing to and maintain than pitched roofs but they come with their one big problem. Rain and snow don't readily flow off them as they do pitched roofs. If there is any kind of crack or leak in your roofing material, you can expect water to seep into the interior of the building. Tar paper, also know as roof felt, is a heavy paper impregnated with tar which makes it waterproof. Tar paper is considered an underlayment, it goes under a more durable roofing material. It acts as an added moisture barrier.
Sweep the bare roof boards clean of any dirt and debris. If any roof boards need replacing, do it now.
Nail aluminum drip edge along all the edges of the roof using 1¼-inch galvanized roofing nails. Drip edge is a metal edging that directs rainwater to drip off the edge rather than seeping back under the tar paper. Drip edging is overlapped at the corners of the roof. For long stretches of roof line multiple sections of drip edge are needed. Overlap one end over the adjoining section an inch and push straight down, locking them into each other.
Roll out a 3-foot-wide strip of ice and water shield along each roof edge. This material is very sticky. Carefully position the front edge of the roll on top of the drip edge and unroll. Once the sticky side makes contact with the roof you can't pull it back up.
Roll out the first section of tar paper over the ice and water shield. Tack it to roof using a hammer stapler or an electric staple gun.
Overlap the next strip of tar paper over the first one by 5 inches and staple in place. Repeat all the way across the roof.
Overlap the tar paper over any metal flashing such as around a chimney or roof vent.
Tar paper can act as temporary protection from rain but the permanent roofing material should be installed over it as soon as possible. Tar paper is particularly susceptible to wind damage if not roofed over.