Consult with your inspector to see whether you need to tear off the old roofing or if you can reroof over the existing roofing. Use flashings approved by your building department. Modified-bitumen roofing may have a granular surface as shown here or it may be smooth. If you install the smooth product, cover it with aluminum coating. These steps show a “torch-down” method, which looks a bit scary but actually is not too difficult. Renting a large propane torch is inexpensive. You can also set the sheets in adhesive; this sounds easier but is actually messier and more time-consuming. Expect to spend one or two days, working with a helper, to lay insulation and modified-bitumen roofing for a 500-square-foot roof. Before you begin, measure and make a drawing of your roof and consult with a dealer. Editor’s tip: Place the propane tank in a central location so that you can work across the roof without having to move the tank during the installation of a sheet. The tank may ice up (propane acts like a refrigerant), which will cause the flame to diminish. If this happens lift the tank and lightly heat it with the torch. If you set the nozzle onto the felt while it is still hot, it may melt the felt or set it on fire. Protect the roof with a rag, set it on a leather work glove, or overhang the nozzle beyond the roof. At all times pay attention to the nozzle when it is flaming or hot. It is possible to start a fire on the roof if you leave a hot or flaming nozzle unattended. Editor’s tip: If a flat roof meets a sloped roof, be sure to configure the flashings and roofing pieces so water has no opportunity to infiltrate as it flows downward. In some cases, this means that flashings will direct water onto the sloped roof. If the old roof worked well, copy its flashing and roofing arrangement. Visualize how water will flow and avoid places where water can puddle or flow under an overlapping roofing piece. If you have a short parapet wall, you can usually roll the roofing sheets up onto it. The sheets cannot make a tight turn, so there should be flashing or built-up roofing in the corners so the roofing can make a gentle, sweeping turn upward. Seal the top of the roofing completely.
