A collateral warranty is a contractual arrangement that is directly connected to another principal contract. In other words, it is “collateral” to the main contractual arrangement. Collateral warranties are particularly popular in the building industry.s most commercial development projects are financed by institutional lenders such as banks, collateral warranties are typically a necessity. Collateral warranty is legally designed to enable a third party with interest in completion of the project to pursue a legal claim against another party involved in that project.