(a) The load bearing capacity of elements or assemblies shall be established by calculations in accordance with generally established principles of engineering design. However, when the composition or configuration of elements, assemblies or details of structural members are such that calculations of their safe load-carrying capacity and basic structural integrity cannot be accurately determined in accordance with generally established principles of engineering design, structural properties of such elements or assemblies may be established by the results of tests that are designed and certified by an architect or engineer, with the test results approved by the department.

(b) When any structural design or method of construction is substantiated by calculations and supporting data, the calculations and supporting data shall be approved by an architect or engineer and shall be submitted to the department.

(c) When the design of accessory structures is substantiated by calculations or tests, all structural plans shall be approved by the architect or engineer in charge of the total design.

(d) When any design or method of construction is substantiated by tests, all those tests shall be performed by an approved testing agency acceptable to the department or shall be directed, witnessed, and evaluated by an independent architect or engineer. All test procedures and results shall be reviewed, evaluated, and signed by an architect or engineer. The approved testing agency, architect, or engineer shall submit the evaluation of test results, calculations, and recommendations, to the department. The department may require that a representative of the department witness the test.