Roll-formed aluminium sections have recently been utilised in structural systems as load-bearing members. Commonly used as flexural members, these sections are vulnerable to various buckling instabilities including web crippling failure. The current web crippling design guidelines are imperial in nature and their suitability for newly developed sections may not be accurate and reliable. Therefore, this study aims to investigate the web crippling behaviour of and design considerations for unfastened roll-formed aluminium lipped channel (ALC) sections under one-flange loading conditions. An experimental investigation was conducted for this purpose based on the AISI S909 web crippling test guidelines. Numerical simulations were subsequently conducted to extend the range of geometrical dimensions and aluminium alloy grades. A detailed assessment of the design rules given in the American, Australian, and European specifications was carried out using the acquired experimental and numerical results. Most of these guidelines were found to yield unsafe and unreliable predictions of the ultimate web crippling capacities, and therefore suitable modifications and improvement were proposed. The modified design rules predictions showed a good agreement with both experimental and numerical results. Hence it is recommended to adopt these improved design guidelines in relevant aluminium standards.