Exterior walls were sometimes built with a fire retardant sheeting in the form of asbestos paper.  If it looks like a thick gray cardboard, it may contain asbestos.  If left undisturbed and in good condition, this sheeting is considered safe.  However, if you are taking out a wall for expansion and remodeling, or if you are replacing siding and shingles, you could release many fibers in the process of drilling, sawing, and removing. Hire professionals for removing this paper. Cement asbestos board (commonly referred to as CAB) has been used in houses as sheets for straight and lap siding and has been cut and shaped as a substitute for wood shingles for roofs and exterior walls. The material is hard and brittle, normally light gray in color, was pre-drilled for fastening, and often was factory primed and painted. Since this material is mainly outside the material, it presents little hazard, unless altered by drilling, sawing, sanding.  When CAB becomes worn or damaged, spray paint it to ensure sealing in the fibers. If you must remove CAB be very careful to wet the material and cut or pull the nails so that damage or breakage of the CAB is minimized. School officials should always consult with their asbestos program manager before disturbing any cement asbestos board (CAB).