Built up roof is a generic term for a roof system that is
literally built by adding layers. Build up roofs can be
installed using different waterproofing materials including
coal tar pitch, asphalt, cold application adhesive, and
modified asphalt. All systems will utilize either base sheet,
ply sheets (felts), or cap sheets in some combination. The roof
has a variety of surfacing options ranging from gravel,
asphalt, coatings, to mineral surfaced.