What is the primary issue with insulation that is poorly fitted to its cavity?

When insulation is poorly fitted to its cavity, the primary issue that arises is decreased energy efficiency. Properly installed insulation acts as a barrier to heat flow, which helps maintain the desired temperature inside a building. However, when insulation is not fitted correctly—such as gaps, compressions, or misalignments—it can create thermal bridges that allow heat to escape in the winter and enter in the summer. This results in an increased energy demand for heating and cooling systems, leading to higher energy costs and making it more challenging to maintain a comfortable indoor environment.

In contrast, while poorly fitted insulation may indirectly affect costs or moisture levels, those are secondary consequences. Efficiency of insulation is fundamental to its purpose. Enhanced structural support is not a concern tied to the fitting of insulation; rather, insulation is designed to provide thermal resistance and comfort, not structural integrity. Thus, the most significant impact of poor insulation fitting is the loss of energy efficiency.