Full basement foundations involve excavating below grade to create an entire basement level that can be finished for living space or reserved for mechanical systems. Excavation depth is typically 7 to 10 feet below grade to accommodate both the basement space and required footing depth below frost line. Typically, footings extend 3 to 4 feet below grade in colder climates to prevent frost heave damage. Foundation walls are constructed of concrete blocks, poured concrete, or stone with mortar. Concrete block walls typically have cores filled with grout or concrete. Poured concrete walls are monolithic and provide superior water resistance. The walls must be designed to withstand lateral pressure from backfill soil. Lateral earth pressure increases significantly with depth and wall thickness increases accordingly. Concrete walls are typically 10 to 12 inches thick for residential basements and may be thicker for deeper excavations. Reinforcing steel in walls provides tensile strength to resist cracking. A waterproofing coating is applied to the exterior of below-grade walls to prevent water infiltration. Some systems use internally applied waterproofing products. Perimeter drainage is critical; a perforated drain pipe around the foundation footings collects groundwater and directs it away. A sump pump may be installed to remove groundwater that accumulates in the lowest point. Interior floor drains are sometimes installed in basements that could flood. The basement slab is typically a 4-inch concrete floor with a vapor barrier beneath for moisture control. Windows or window wells provide light and egress if needed for livable space. The basement ceiling is attached to the floor joists above, which provide support for the first floor.