A recent webinar on the “10% Rule” included in the 2018 International Existing Building Code (IEBC), attended by the author, discussed an exception in the code’s Section 502.5 that allows existing structural elements to remain unaltered if an addition to that structure results in a less than 10% increase in the element’s demand-to-capacity ratio. After the webinar, there remained the question, where was the companion webinar, the “5% Rule?” The 5% rule, otherwise known as the Prescriptive Compliance Method, is more straightforward and widely used. It is contained in IEBC Section 502.4 and states the following: …