Flat roofs sometime show signs of age-related deterioration, patching various leaks may be an ongoing project. If this is the case, it may be time to call in a professional to replace the entire roof. On the other hand, if a leak is caused by either a lifted section of roofing felt, a tear or crack in the material, or a faulty section of galvanised flashing, you can successfully repair the roof yourself.
Examine your roof carefully. Although the roof may appear flat, it has a gradual slope to assist run-off. Also, because water travels, the leak may not be directly above the room with a dripping ceiling or damp walls. Sweep roofing chips to one side with a stiff-bristle broom. Look for blisters, cracks and tears or lifted seams in the roofing felt. Mark any suspect areas with a piece of chalk. Inspect all galvanised metal flashing around the perimeter, vent pipes and chimneys for raised or damaged sections. Look for evidence of dried-up standing water. These areas are indicated by concentric rings of dirt left behind when pooled water evaporates.
Cut out a square of new roofing felt with a pair of heavy scissors. The patch should overlap the blistered area by 2 inches on all sides. Round off the corners of the patch. Apply a thick layer of bitumen cement to the roof surface with a 2-inch paintbrush and carefully position the patch over the repair. Using the rubber roller, roll lengthwise and crosswise, but don't press hard enough to squeeze the adhesive out. Coat the edges of the patch with a 2-inch-wide overlapping layer of bitumen adhesive. Sprinkle roofing chips over the repair.
Lift any loose overlapping seam. Clean out debris with the1/2-inch paintbrush and treat with fungicide. Apply bitumen adhesive to the underside and flatten with the rubber roller. Place a thick plank over the repair and weigh it down with a couple of buckets filled with water to prevent the seam from curling back while the adhesive cures. Leave overnight. Apply a 2-inch overlapping patch of felt to the seam. Coat the seam with another 2-inch-wide layer of bitumen and sprinkle with roofing chips.
Sweep identified water-pooling areas thoroughly with a stiff-bristle broom. Apply a liberal coating of fungicide and allow enough time to dry. Following the manufacturer's directions, pour enough bitumen or mastic-based roofing compound into depressions to cover the pooling area. Allow time for the material to settle and then spread roofing chips over the area.