What will likely reduce energy bills in areas already insulated, such as an unfinished attic floor?

Adding more insulation is a method that can certainly reduce energy bills, particularly in areas that are already insulated, like an unfinished attic floor. Proper insulation helps to maintain the desired temperature inside a home by minimizing heat transfer. In cases where the existing insulation may be inadequate, adding more insulation can significantly improve the thermal barrier, making it more difficult for heat to escape in the winter and for heat to enter in the summer. This leads to less energy being used for heating and cooling, ultimately resulting in lower energy bills.

While sealing gaps and cracks is also a beneficial practice for improving energy efficiency, the specific question places emphasis on areas that are already insulated. Gaps and cracks may allow drafts that can reduce the effectiveness of insulation, but the focus here is on enhancing the insulation itself rather than addressing those gaps. Similarly, installing energy-efficient windows and upgrading the HVAC system can also lead to energy savings, but these measures target different aspects of the home's energy use. In this context, enhancing the insulation directly correlates to improved energy efficiency for the space. Thus, increasing the amount of insulation is the most direct and relevant action to further reduce energy bills in an already insulated area like an unfinished attic floor.