This study investigates the web crippling behaviour of cold-formed steel (CFS) back-to-back built-up U-shaped sections with perforated webs. In this research, the web opening was positioned at the mid-height of the web directly beneath the bearing plate. Initially, the geometrically and materially nonlinear finite element (FE) models were validated against 24 experimental tests from the literature, demonstrating excellent agreement. Specifically, the mean FE-to-experimental strength ratios (PFE/PEXP) were 1.002 and 1.001 for the Interior-Two-Flange (ITF) and Interior-Loading (IL) conditions, respectively. Subsequently, the verified nonlinear FEM models were employed to conduct an extensive parametric study comprising 198 built-up I-sections. Moreover, this extensive investigation systematically examined the effects of various parameters, including hole size, the presence of unstiffened and stiffened holes, as well as different hole shapes such as rectangular, slotted, circular, and square openings, on web crippling performance. Furthermore, the results indicate that unstiffened holes can reduce the web crippling strength by as much as 54 % compared to plain webs. In contrast, edge-stiffened holes can enhance the web crippling strength by up to 42 % relative to plain webs. These findings highlight the significant impact of web perforation geometry and stiffening on the web-crippling behaviour of CFS built-up sections.