Renewable Biomass Facilitation Act of 2008 - Amends the Clean Air Act to redefine the term "renewable biomass" as: (1) materials, precommercial thinnings, or exotic species that are removed as byproducts of preventive treatments to reduce hazardous fuels, to reduce or contain disease or insect infestation, or to restore ecosystem health, that would not otherwise be used for higher-value products, and that are harvested from National Forest System land or public lands in accordance with federal and state law, land management plans, and requirements for old-growth maintenance, restoration, management direction, and large-tree retention under the Healthy Forests Restoration Act of 2003; or (2) any organic matter that is available on a renewable or recurring basis from non-federal land or Indian land held in trust by the United States or subject to a restriction against alienation imposed by the United States, including renewable plant material (including feed grains, other agricultural commodities, other plants and trees, and algae) and waste material (including crop residue, other vegetative waste material, animal waste and byproducts, and construction, food, and yard waste).