A Party Wall is a wall between neighboring buildings with ratings that vary by occupancy: commercial and residential.

• A. 1 hour
• B. 4 hours
• C. 2 hours
• D. 3 hours

Answer: (C)

Understanding fire-resistance ratings for walls that separate different occupancies is the key here. A party wall’s job is to slow the spread of fire from one space to another and keep structural integrity long enough for people to evacuate and for firefighters to operate. When the spaces have different uses—commercial and residential—the potential fire loads and risk profiles are higher, so the separating wall is typically required to have a greater level of fire resistance.

Two hours is the common fire-resistance rating for a party wall between commercial and residential occupancies. This duration provides a practical balance: it offers meaningful protection against fire spread and preserves life safety and property without requiring the more stringent and costly higher ratings that are used in more extreme or special cases.

One hour is usually associated with interior partitions within the same occupancy, where the risk and exposure are lower. Three or four hours appear in more demanding scenarios, such as certain fire walls or exterior separations with higher exposure or hazard levels. So for a mixed commercial-residential party wall, two hours best fits the required protection level.