The application of built-up roofing is a specialized operation that requires particular experience and special equipment; it is therefore advisable to employ an experienced roofing concern to lay or repair this type of roofing.
Built-up roofings are used for roofs with a low pitch and consist of several layers of bituminous impregnated felt, lapped and cemented together with a bitumen which is usually heated. Fine gravel or slag is then spread over the top layer to provide a weathering surface. If properly applied, built-up roofings should not require major repairs or for or a long time.
When a leak occurs in a built-up roof, flashings at parapet walls, skylights, and vents should be carefully inspected, because the initial failures usually occur at these locations. Bituminous flashings are made of saturated felt and flashing cement. Flashing cement should be forced behind the felt if it has separated from the wall at the upper edge, and the edge sealed with a strip of bituminous-saturated cotton fabric 4 inches wide, embedded in and coated with flashing cement.
A break in the flashing should be repaired by applying saturated flashing felt in pieces extending not less that 6 inches in all directions beyond the break, cementing it to the flashing and coating it with flashing cement. Sheet-metal flashings which have a ferrous-metal base, such as zinc-coated sheet iron, should be painted with corrosion-resistant paint or, if badly weathered, replaced with new flashing.
Bare spots on a built-up roof where the mineral surfacing is not properly embedded should be swept or scraped clean, a heavy coating of hot bitumen applied, and additional gravel `or slag spread over the area.
Felts which have disintegrated should be cut away and replaced with new felt of the same kind. The new felt should be mopped in place, allowing at least one additional layer of felt to extend not less than 6 inches beyond the other layers.
When necessary to resurface a built-up roof, the old roofing may be left partly in place or removed entirely. If left in place, the mineral surfacing should be scraped off and removed and the entire roof swept clean. Holes or cracks in the old roof covering should be mopped with hot bitumen and covered with roofing felt followed by another application of bitumen before the new roofing is applied. If the old roofing is to be entirely removed, the deck should be repaired and made ready for new roofing. In either case, the new roofing should be applied according to manufacturer’s specifications and directions.