What is the maximum distance an underground main can be installed under the building to the riser location without additional requirements?

According to NFPA 13, Standard for the Installation of Sprinkler Systems, underground piping installed beneath a building generally requires specific protection methods, such as being placed in a concrete trench or enclosed in a pipe sleeve. However, the standard provides an exception for short pipe runs. If the length of the underground pipe extending under the building to the system riser is 10 ft (3 m) or less, these additional protective measures are not required. This exception facilitates installations where the riser is located just inside a foundation wall.

A. 2 ft (0.6 m): This distance is overly restrictive and is not the maximum allowance specified in the NFPA 13 standard.

B. 5 ft (1.5 m): This value is less than the maximum permitted distance; the standard allows for a longer run before requiring protection.

D. 15 ft (4.6 m): Any pipe run exceeding 10 ft (3 m) under a building would mandate the implementation of additional protective measures.

1. NFPA 13, Standard for the Installation of Sprinkler Systems, 2022 Edition. Section 10.4.3.1.1 states, "Where the pipe is not more than 10 ft (3.0 m) in length under the building, the requirements of 10.4.3.1 shall not apply."

2. NFPA 13, Standard for the Installation of Sprinkler Systems, 2019 Edition. Section 10.4.3.1.1 provides the identical exception: "Where the pipe is not more than 10 ft (3 m) in length under the building, the requirements of 10.4.3.1 shall not apply."

3. Oklahoma State University, College of Engineering, Architecture and Technology. Fire Protection & Safety Engineering Technology (FPST) course materials for FPST 3333, Water-Based Fire Protection Systems. Course lectures on underground piping installation reference the exceptions outlined in NFPA 13, Chapter 10, including the 10 ft (3 m) rule for unprotected pipe under a building.