Where should carpet cushion (pad, underlay) be secured to the subfloor in a stretch-in installation?

The correct choice is to secure the carpet cushion along the edges and at seam locations. This method is essential for maintaining the stability and integrity of the carpet installation.

Securing the cushion along the edges helps to keep it in place, preventing movement that could lead to buckling or wrinkles in the carpet over time. Additionally, fastening the cushion at seam locations is crucial because seams are often points of stress where the carpet can shift or separate if not adequately supported. Ensuring these areas are secure minimizes the risk of damage and provides a smoother, more stable surface for the carpet itself.

This approach promotes proper performance and longevity of the carpet installation, aligning with best practices in the industry. The other options do not adequately address the need for security at critical points throughout the installation, which can compromise the overall quality and durability of the flooring.