Duplex and legal units are separated by a ________.

Duplex and legal units are typically separated by a firewall that extends up and into the attic. This type of firewall serves as a crucial safety feature, providing the necessary fire protection between the two units. It is designed to prevent the spread of fire from one unit to another and is often constructed to meet specific building codes and standards regarding fire resistance.

By extending into the attic, the firewall helps ensure that there are no gaps or openings that could allow fire to travel upward and potentially compromise safety by reaching other sections of the building. This construction method is especially important in multi-family dwellings and ensures compliance with local fire safety regulations.

Other types of walls, such as partition walls or common walls, may not have the same fire-resistance characteristics as a properly constructed firewall, which is specifically engineered for this purpose. Thus, the focus on fire safety makes the firewall the correct choice in this context.