What’s the difference between NFPA 13 and 13R?

Assuming sprinkler protection is required; which for most buildings constructed in this manner building size, height, and occupancy will typically require it; a key decision point is determining if NFPA 13 is needed or if NFPA 13R can be used. The primary philosophical difference between the two is that NFPA 13 has a dual purpose of property protection and life safety while NFPA 13R has the purpose of providing life safety. The video below explains some of this difference.

While the difference might seem subtle there can be a great deal of savings based on the allowances of NFPA 13R. A major perceived benefit in using 13R can be the omission of sprinklers in areas that NFPA 13 requires sprinklers including small closets, concealed spaces, and attic spaces. These attic sprinklers are where a lot of complexity can come in since they will often require a dry system, or at least some other form of freeze protection, resulting in increased up-front costs and more long-term testing and maintenance considerations. NFPA 13R systems can also result in decreased water demands and therefore result in smaller pipe diameters. A very good analysis of the differences between NFPA 13, NFPA 13R, and NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes can be found here.

Where can NFPA 13R be used in podium construction?

The podium portion of the building will need to be protected by an NFPA 13 sprinkler system. Where 3-hour separation is provided at the top of the podium as required by building codes, the upper residential portion can then be evaluated as whether it is within the scope of NFPA 13R. This includes residential occupancies that are up to and including 4 stories in height and located in buildings not exceeding 60 ft (18 m) in height above grade. If it falls within this criteria, then NFPA 13R can be utilized for the protection. While the maximum building height above grade is fixed based on the definition of height above grade, the stories themselves can be counted from the 3-hour horizontal separation. The figure below demonstrates the differences in this criteria. It is important to note that the 2021 edition of the International Building Code limits the allowance of NFPA 13R where the limitation is four stories above grade plane. This is a significant change that impacts the application of the standard. A more in-depth analysis on this can be found here.

Still a design decision

Even if 13R is permitted, nothing would prohibit the use of NFPA 13 to provide added property protection required by that standard. In fact, there are building code trade-offs that can only be used with NFPA 13 systems; and the ability to take advantage of those is not available when NFPA 13R is used. Even where that is not the case, there are cost benefits but it is important to understand the goals of NFPA 13R. While a fire in a living space should be controlled as it would be with a NFPA 13 system, a fire originating in a concealed space or in an unsprinklered attic can result in the loss of the building. If all occupants are able to safely evacuate, the system has done its job even if the building is a complete loss, whereas an NFPA 13 system should be able to protect the occupants and provide property protection.