Proposed Guidelines for Clearance Holes, Slots, and Washers

This report provides interim guidance for the specification of clearance holes, slots, and washers in solar photovoltaic (PV) mounting structures. It clarifies the relationship between traditional structural joints governed by AISC and RCSC provisions and alternative structural joints commonly used in PV systems that fall outside those standards. For alternative structural joints, the report outlines design considerations for hole geometry, washer dimensions, material hardness, and thickness. It also describes common failure mechanisms, including compressive yielding and washer bending over oversized holes or slots, and presents recommended practices and a design checklist to support rational joint specification.