A detail-oriented home inspector, who is inspecting a newer multi-unit dwelling, will look for a party wall between units. Now, that information applies to newer buildings, built in the last few years. Many older duplexes and condos had no such fire protection.

The party wall is viewed from the attic, assuming there is access to do so. The party wall acts as a firewall by blocking the area, at each unit, from above the ceiling up to the roof. So, in a duplex, there would be one wall down the center and there would be two such walls at a triplex. That way, if a fire starts in one unit, while it might travel, it is slowed down by the wall.

You might be thinking that wood is flammable. True, but the design blocks the area off so roof ventilation from the other units does not "draw" the fire. Think about it, roof ventilation, to a fire, is like a chimney. As stated before, this applies to newer homes. In older buildings, access to one attic hatch often lets a person into the attic above every single unit in the complex – no party or firewalls. In fact, if there is more than one attic hatch, that can be a security issue and might allow someone who gains attic access to enter other people’s spaces. Movies, with various villains or cat burglars, have made the most of that potential security breach over the years.