What is the correct method for installing double layers of rigid board insulation?

The correct method for installing double layers of rigid board insulation is to stagger and offset the boards. This approach creates a more effective thermal barrier by reducing thermal bridging. When the seams of one layer are offset from the seams of the layer beneath it, it minimizes the potential for heat loss through those seams.

Using a vertically staggered and offset installation allows for increased continuity of the insulation layer, ensuring that there are no straight lines where heat can escape. This method helps maintain overall thermal performance and contributes to the energy efficiency of the building envelope.

The other options may compromise insulation effectiveness or structural integrity. For instance, aligning layers horizontally and flush could create straight seams that allow for thermal bridging, reducing the insulation’s effectiveness. Similarly, overlapping without alignment might not provide a tight seal, and installing in a single continuous layer fails to take advantage of the benefits provided by staggered seams, which enhances the overall insulation performance.