The increasing electrification of heat in buildings poses significant engineering and societal challenges, requiring innovative solutions to enhance the associated transition. Paramount to this change is likely to be energy efficiency and energy flexibility. Phase change materials (PCMs) offer promising potential in demand response (DR) strategies by storing and releasing thermal energy, thereby shifting energy consumption away from peak periods. However, significant research gaps exist in optimising PCM properties, particularly the impact of the melting temperature range on energy flexibility in residential buildings. This study evaluates the thermal behaviour of PCMs with melting ranges between 2 °C and 8 °C in a cooling-dominated scenario in a residential building. The methodology utilises an EnergyPlus model. The results indicate that a wider PCM melting range (8 °C) achieves up to 0.32 kWh of power curtailment during extended DR events, outperforming narrower ranges. Additionally, a 2-h precharging strategy results in a peak demand reduction by 5% compared to a 1-h precharging period. These findings provide insights into optimising PCM-enhanced building envelopes for improved load shifting, reduced HVAC consumption, and enhanced grid interaction, supporting global energy efficiency and decarbonisation objectives.