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Author(s): Matt Klaus. Published on July 1, 2017.

Which NFPA sprinkler installation standard is best for townhouses?

BY MATT KLAUS

Townhouse construction is on the rise again—according to U.S. Census Bureau data, building starts for townhouses last year were up nearly 13 percent nationwide over those in 2015. With the increase in this construction comes the question of what type of sprinkler system is the best fit for these homes.

NFPA produces three different sprinkler system installation standards that could be used for the design of a sprinkler system in a townhouse. Ultimately, the options available to the architect and design team are based on allowances from the building code as well as on the construction features considered in the design.

While NFPA 13, Installation of Sprinkler Systems, is certainly an option for townhouse construction, the most commonly used standards for this style of home are NFPA 13R, Installation of Sprinkler Systems in Low-Rise Residential Occupancies, and NFPA 13D, Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes. In some instances, states or municipalities mandate whether NFPA 13D or NFPA 13R can be used, based on the language included in the building code or in a local amendment. In other instances, decisions made by the design team may dictate the options that are available.

The characteristic of townhouse construction that will most likely determine whether an NFPA 13R or NFPA 13D system must be installed is how the dwelling unit separations are constructed. If the townhouses are constructed in accordance with a building or residential code, where each townhouse unit (or every two units creating a “duplex” arrangement) is considered a separate structure due to the use of appropriate fire-resistance-rated construction separating each of the units, NFPA 13D may be acceptable. In this case, each individual townhouse (or every two units) would be considered a separate building in accordance with the building code and therefore the scope of NFPA 13D, which limits the application of the standard to one- and two-family homes, would be satisfied. In instances where more than two townhouses are considered to be in a single building based on the way the dwelling unit separations are constructed, NFPA 13R or NFPA 13 must be used.

There are several benefits to designing a townhouse sprinkler system to NFPA 13D versus NFPA 13R. NFPA 13D allows for the hydraulic calculations to consider either one or two sprinklers as opposed to the four required by NFPA 13R. By including fewer sprinklers in the hydraulic calculation, the water supply is not required to be as robust, which can help save money on piping by using smaller diameter pipe or on sizing a tank if that is the desired water supply. NFPA 13D also allows for the use of different piping materials, such as half-inch cross-linked polyethylene (PEX), which is flexible and can be installed relatively quickly.

The potential cost savings associated with installing an NFPA 13D system would need to be weighed against the costs of the fire-resistance-rated construction that creates the “separate buildings” arrangement. In many cases, making each townhouse a separate building requires the construction of structurally independent firewalls or back-to-back exterior walls, both of which are more expensive than the fire-resistance-rated dwelling unit assembly permitted by many jurisdictions. If the design team has already included these construction features in the design, NFPA 13D might be a good option. If they are not included, an analysis of the cost of the different types of sprinkler systems versus the cost of the different rated assemblies should be performed.

In some instances, although not mandated by most codes, an NFPA 13 system might be a good fit for larger townhouse projects. NFPA 13 systems are designed to provide both property protection and life safety; the two residential standards, by comparison, were written with life safety as the sole purpose. Where property protection is an important part of the equation, the design team may want to include the consideration for an NFPA 13 system in any cost benefit analysis that is conducted in regards to selecting the best sprinkler system for the needs of the project.

MATT KLAUS is NFPA technical services lead for fire protection engineering.