A listed flame spread index of ____ or less is required when codes specify fire retardant treated wood.

The requirement for a flame spread index of 25 or less for fire retardant treated wood is based on building codes and safety regulations aimed at minimizing fire hazards in residential construction. Fire retardant treated wood is specifically designed to slow down the spread of flames, giving occupants more time to escape and limiting property damage during a fire.

A flame spread index of 25 or less indicates that the material has been tested and found to possess adequate fire-resistance properties. This level of performance aligns with the standards established by the National Fire Protection Association (NFPA) and various building codes, which categorize materials based on their flame spread characteristics.

In practical terms, this means that when fire retardant treated wood is utilized in construction, it must effectively contribute to fire safety by resisting ignition and slowing the flame spread to help protect both life and property.