A significant number of older homes in the Netherlands are proving to be energy inefficient due to inadequate insulation. Nearly a quarter of homes built before 1945 carry the lowest energy efficiency ratings of F or G. This poor insulation is resulting in substantially higher energy bills for homeowners, potentially adding hundreds of euros to annual costs. The provinces of Drenthe, Friesland, and Zeeland have a disproportionately high concentration of these poorly insulated properties. The findings highlight the financial burden placed on owners of older housing stock as energy prices rise. Experts suggest improvements to insulation are crucial to reduce energy consumption and lower household expenses. The issue underscores the need for renovation and energy-saving measures in the existing building sector.