What is the minimum required fire resistance rating for the wall separating units in a non-sprinklered two-family dwelling?

In a non-sprinklered two-family dwelling, the minimum required fire resistance rating for the wall separating the units is set at one hour. This requirement serves to help prevent the spread of fire and smoke between the two units, thus enhancing the safety of the occupants. A fire resistance rating indicates the duration that a building element can withstand a standard fire test without collapse, which is critical in shared walls to protect both sides effectively.

A rating of one hour is standard practice as it provides adequate time for occupants to evacuate safely and for emergency services to respond to a fire incident. This level ensures that if a fire starts in one unit, there will be a reasonable time buffer to allow the other unit to remain protected from the fire's immediate effects.

The other options either do not meet the necessary standards or provide insufficient protection. For example, a rating of 30 minutes does not provide the level of safety required in this scenario, while a two-hour rating exceeds what is necessary, creating unnecessary cost and complexity in construction.