Foundation (engineering)
Foundations are designed to have an adequate load capacity depending on the type of subsoil/rock supporting the foundation by a geotechnical engineer, and the footing itself may be designed structurally by a structural engineer. The primary design concerns are settlement and bearing capacity. When considering settlement, total settlement and differential settlement is normally considered. Differential settlement is when one part of a foundation settles more than another part. This can cause problems to the structure which the foundation is supporting. Expansive clay soils can also cause problems.
Construction loan
Beyond this guideline, the next most common rule is a minimum cash injection requirement. Even if, for example, a business might be able to afford a monthly payment of a loan high enough to pay for the entire construction project, many lenders would require them to instead use a certain minimum portion of their own cash to complete the project. The reason for this is both to psychologically and economically tie in the owner with the project (hopefully making it less likely that they would walk away from the project if something goes wrong), and to give the lender a cushion whereby if something goes wrong they are more likely to be able to sell the real estate at a value that would better cover the loan amount. This guideline is often termed a "loan to cost" requirement, i.e. the lender will only loan up to 85% of the project costs.