Foundations and the extensive site work often needed to prepare for them can be costly, particularly where it is hilly and in areas with shallow soils. Slabs are often one of the cheapest methods to build a foundation. Many contractors in the area prefer to construct four-foot frost walls under the slab. However, frost-protected shallow foundations (i.e. monolithic concrete slabs for heated structures) are a way to minimize the depth of excavation and potentially save in costs. The addition of insulation along the exterior of the foundation (both vertical and horizontal), as shown in Figure 1, protects against frost damage.
A comparison of average foundation costs, according to Home Advisor, suggest that a monolithic concrete slab is about 22% the cost of a full basement poured concrete foundation, based on national average prices.