When a roof begins to leak a check of the roof will be necessary to see what kind of repairs it will need. Examine the roof to see what type of materials are on it and whether or not a sealant like Elastomeric can be used, or if adding a new layer of rolled roofing will be possible instead of removing and replacing the roof. This can be done if there has only been one layer of roofing applied. If too many layers have been applied, replacing the roofing will be necessary.
Planning the Flat Roofing
Start by removing the existing roofing materials. While removing these materials, set aside any that are in salvageable condition. Many times the drip edge, which is attached to the perimeter edge of the roof and is under the roofing material, can be reused. Measure the roof, both lengthwise and widthwise to get the area in square feet. This will let you know how much felt paper and roll roofing to buy. If the drip edge is savable you will not need to replace it, but if it is not, take a linear measurement of the perimeter edge. This will be the amount of edge you will need to buy. Typically, drip edge comes in 10-foot lengths. Depending on the size of the roof, you will also need to purchase two to three pounds of simplex roofing nails and between two and five gallons of roofing tar.
Laying Down the Felt Paper
Whether you are laying over the other roofing surface or not, it is always best to use felt paper when putting down a new roof. Roll the felt paper along the bottom edge of the roof, working in a lengthwise direction on the roof. Nail the top of the paper down. Lay the next strip of paper down, overlapping the second piece about four to six inches over the first layer. Continue nailing the strips down until the roof is covered. Cap the roof with the drip edge covering the top edge of the felt paper and secure it tightly to the roof with nails.
Finishing the Flat Roof
Before laying the roll roofing, run a bed of roofing cement along the edge about three to four inches wide, making sure to cover where you nailed the drip edge. To lay the roll roofing, start at the bottom edge and work lengthwise up the roof as before. Make a mark four inches down from the top of your first layer. Measure the width of the layer and put a mark that far up from the mark you just made; do this at each end. Using a chalk box and strike a line across the felt paper to mark a line that you will follow to keep your next layer straight. Continue this up to the top, and lay down the strips of roll roofing and nail the top edge. When you reach the other side of the roof, nail it down and then cement over the outer edge to seal it. Check the roof for any protrusions such as pipes and vents, and cement around them to avoid leaking later.