Roof Removal Before Building Demolition
On occasion one may find that the roof of a building being demolished is removed before the building is razed. Such removal may be required when buildings are very close to one another, or when the roofing contains asbestos-containing materials.
There are two major types of roofing: "built-up roofing" and "sheet goods."
Built-up roofing contains multiple layers of felt and asphalt. Sheet goods typically consist of a single layer of material.
Courtesy of The EPA

Roof Removal Procedures for Asbestos