A material that isn't capable of igniting and burning. Metal siding and traditional three-coat stucco are examples of materials that are rated as noncombustible. Given the widespread use of composite materials -- that is, a material that is made from a combination of a few different materials, such as a fiber-cement product -- it isn't always clear whether a material is noncombustible. ASTM E-136 is a standard test procedure that is used to determine if a material qualifies as noncombustible. If in doubt, look to see if this standard is referenced. For example, technical data sheets for fiber-cement products, such as Certainteed Weatherboard and James Hardie HardiePlank siding products, state that they qualify as a noncombustible material, according to ASTM E-136.
A fiber-cement horizontal lap-siding product.
A fiber-cement lap siding product after a fire test that consisted of a flame contact exposure. The material did not ignite. Small vertical cracks developed as a result of thermal contraction.