For attaching cement backer-board to a sub-floor, what is the minimum length of screws to be used at the edges?

Using 2-inch screws for attaching cement backer-board to a sub-floor is based on ensuring a secure and stable installation. When securing backer-board, it is crucial to penetrate through the board and into the sub-floor adequately, providing a strong mechanical connection.

The minimum length of 2 inches allows for sufficient grip in the sub-floor material, which is often plywood or oriented strand board (OSB), ensuring that the backer-board remains firmly in place. This helps to prevent movement or loosening over time, which is essential for a flooring system meant to withstand moisture and the stress of foot traffic.

In contrast, shorter screws might not achieve the necessary depth of penetration into the sub-floor, leading to potential issues with the integrity of the flooring installation. Therefore, using 2-inch screws is a standard recommendation for achieving optimal performance and durability in flooring applications.