Question

when are extension jambs most likely to be needed? when casement windows are used when the window opening is too high when the new window is not as wide as the old window when a modern replacement window is installed in an older building

Explanation:

Extension jambs are used to fill the gap between the window frame and the wall. In older buildings, the wall thickness might be different from modern window frames. When installing a modern replacement window in an older building, extension jambs are often needed to ensure a proper fit and seal. Casement windows don't inherently require extension jambs. A window opening being too high is more about installation height rather than jamb extension. A new window not being as wide as the old one is about width adjustment, not jamb extension.

Answer:

when a modern replacement window is installed in an older building