Independent tests carried out by the Forest Products Laboratory, a division of the U.S. Department of Agriculture, proved the pressure-impregnated shakes and shingles showed no significant loss of fire-retardancy after 10 years of continuous severe outdoor weathering.

In 1991, a home in Malibu, Calif. was found to have Class C pressure-impregnated fire-retardant cedar shakes that were 16 years old. Those shakes were removed from the home and tested by today's standards. They passed the Class C test with flying colors. (It's interesting to note that fire officials from Southern California were invited to attend the test but declined the invitation)....