Installing any type of roof, laying down the felt underlayment is always one of the first steps. This underlayment is used as a water barrier and helps protect the roof from leaking. Putting down felt on a flat roof is similar to laying it down on a sloped roof. Flat roofs can be easier to work with and less time consuming. Any homeowner with the proper instructions can lay down a flat roof.
Pull up all the existing felt from the roof with a hammer or pry bar to remove it. Remove all nails that are set in place. Pull up all three layers of existing felt, being careful not to pull up the plywood underneath.
Lay out the second piece and overlap it a few inches. Nail it on the roof in the same manner as the first and continue down the roof until you reach the edge. Cut the felt to size at the end with a utility knife if necessary.