How far should the top of an extension ladder extend above the edge of a roof when accessing a building?

The correct height for the top of an extension ladder to extend above the edge of a roof is 3 feet. This guideline is significant for ensuring safety while working at heights. The additional height provides a stable and secure point for the worker to step onto the roof, minimizing the risk of slipping off the ladder or miscalculating the reach.

When a ladder extends adequately above the roof's edge, it not only helps in providing a safe transfer from the ladder to the roof, but it also allows for better stability while the worker is on the ladder. This practice is essential in preventing accidents that could result from an inadequate extension of the ladder. Safety regulations typically establish this standard for extension ladders, emphasizing the importance of proper setup in preventing falls.

In considering the other choices, while they represent various heights that could theoretically be safe, 3 feet is a widely accepted and standard measurement for this type of task in ladder safety protocols.