Windows used as guardrails: a subtlety worth knowing In relation to guardrail conditions or walls acting as guards, what is an infill panel? → Answer When a horizontal mullion (transom) or handrail is located at guardrail height or below, the glazing beneath that mullion will act as an infill panel. Infill panels are subject to concentrated load requirements equal to half of the guardrail load, in addition to wind load. What this means in practice The interior glass lite of the insulated glass unit will generally need to be tempered. For balustrades, the glazing must be tempered or laminated; refer to CSA A500, Table 6.1. Disclaimer: this is provided for informational purposes only  and each project must be verified by a qualified engineer