Fox Blocks are listed in the building codes (IRC- Sections R404, R611 or NBCC Part 9) with specific applicability limits for residential construction. If the project meets the applicability limits within the building code, a Professional Engineer may not be required (dependent on local building department requirements). A building official has the right to request engineering and in some regions all projects require a professional’s stamp. For any projects that exceed the applicability limits, a Professional Engineer is required for the structural design. Check with your local building department.