What is the ideal condition for attic insulation depth to prevent heat loss?

The ideal condition for attic insulation depth to prevent heat loss is indeed above the top of floor joists. When insulation is placed at this level, it creates a barrier that helps to keep warm air in during the winter and cool air in during the summer. This depth ensures that the insulation effectively reduces thermal bridging, which occurs when heat is transferred through structural elements such as the joists themselves.

Insulation that is level with or less than the tops of the floor joists is likely insufficient to provide the necessary thermal resistance, leading to potential heat loss, especially in colder climates. By ensuring that insulation extends above this level, homeowners can better regulate their home's temperature, enhance energy efficiency, and reduce heating and cooling costs.