The NFPA 13 Soffit and Cabinet Rule, as explained by NFPA Joe on YouTube, dictates the placement of sprinkler heads in relation to obstructions like soffits and cabinets. The Soffit Rule specifically addresses how to place sprinkler heads to spray under obstructions against a wall, using a formula to calculate the optimal distance from the side of the obstruction to the center of the sprinkler head. This rule applies to obstructions less than 30 inches in width. The Cabinet Rule focuses on obstructions not exceeding 24 inches in width, and it outlines the maximum distance from the wall to the center of the sprinkler head to ensure adequate coverage. Both rules aim to provide sufficient sprinkler coverage while minimizing unnecessary installations.