Retrofitting double glazed windows can greatly improve comfort, but common mistakes often reduce their effectiveness. One frequent issue is overlooking the condition of existing frames, which may cause air leaks or poor insulation if not assessed properly. Another mistake is ignoring ventilation needs, leading to condensation and moisture problems over time. Poor measurement and rushed installation can also affect alignment and sealing quality. At the midpoint of planning, understanding Retrofitting Double Glazed Windows requirements helps ensure compatibility with the building structure. Skipping professional assessment, using incorrect glazing thickness, and neglecting acoustic needs are further errors that impact long-term performance, durability, and overall energy efficiency.