Section R401 of the IRC establishes foundation requirements for residential buildings. Foundations must extend below the frost line, which varies by climate and typically ranges from 2 feet in warm climates to 4-5 feet in cold climates. The code specifies frost depths by location on a map provided in the code or established by local jurisdictions. Foundations must be constructed on undisturbed earth or properly compacted fill material that has been verified to support the building loads. Foundation materials include concrete, masonry, or untreated wood (for buildings built on posts). Concrete foundations are typically poured in place and must include footings extending below the frost line with minimum 12 inches of bearing width. Concrete compressive strength is typically specified as minimum 2,500 pounds per square inch for most residential applications. Reinforcement is required in certain concrete footing designs where bearing capacity is low or when footings bridge over areas of different settlement potential. Masonry foundations constructed of stone, brick, or concrete masonry units must be mortared with mortar composed of cement, sand, and water meeting ASTM standards. Masonry foundation walls are typically 8 inches thick for single-story residences and 12 inches for two-story buildings. Crawlspace foundations built on posts are permitted for certain building types and locations where adequate clearance under the building is provided. All foundations must be protected from water infiltration by grading that directs surface water away from the foundation and by subsurface drainage systems where groundwater is present.