Standardizing NFPA 13

NFPA 13-2016 is applicable to all sprinkler system designs and installations, with the exception of sprinkler systems in low-rise residential buildings and one- and two-family dwellings and manufactured homes.

By Raymond A. Grill, PE, FSFPE, LEED AP; Arup, Washington, D.C. October 29, 2018

Learning objectives

  • Become familiar with changes in the 2016 edition of NFPA 13: Standard for the Installation of Sprinkler Systems.
  • Obtain an understanding of the application of NFPA 13 to various building conditions, such as cloud ceilings and skylights.
  • Become familiar with the reorganization of NFPA 13 for the 2019 edition.

Standards that fire protection engineers regularly apply in daily practices are developed years in advance of them actually being adopted and enforced. The 2016 edition of NFPA 13: Standard for the Installation of Sprinkler Systems will not be applicable to your project until the jurisdiction in which you work adopts this specific edition. Many jurisdictions are still applying the 2010 edition.

Jurisdictions that have adopted the 2015 edition of the International Building Code (IBC) typically are applying the 2013 edition of NFPA 13. IBC’s 2018 edition and the 2018 edition of NFPA 101: Life Safety Code adopt the 2016 edition of NFPA 13 by reference.

While most jurisdictions adopt NFPA 13 as part of their building code adoption process, there are some authorities that adopt the most current edition of NFPA standards regardless of the edition of the building code that is applied. Most notably, the Department of Defense (DOD), General Services Administration (GSA), and Department of State typically apply the most recent edition of NFPA standards to their projects. It also may be advantageous from a risk management perspective to apply the most recent edition of a code to a project. There may be areas addressed in the most recent code that aren’t addressed in previous editions that can inform a design.

The most recent edition of a standard is typically considered to contain the latest and best information on the subject. However, if there are changes from the actual standard that are being enforced on a project, it is recommended that any deviation from the adopted standard be reviewed with the authority having jurisdiction (AHJ) during the design process.

Product manufacturers must know what criteria their products will need to meet in the future to either develop new products or modify existing products as appropriate. Installing companies need to know future requirements so they can prepare appropriate training material for their employees.

This article addresses a number of the more significant changes in the 2016 edition of NFPA 13 and discusses the new organization of the 2019 edition. Numbers in parenthesis refer to the applicable section in the 2016 edition of NFPA 13.


The subject of metric conversions was debated extensively during the development of the 2016 edition of NFPA 13. The Correlating Committee established a task group to review the metric conversions within the standard and to make recommendations for potential revisions to enhance usability outside of the United States. Previous editions of the standard used an exact conversion between U.S. customary units and metric (SI) units.

Where it was deemed appropriate by the task group and technical committees, nominal metric equivalents or approximate conversions have been provided. The standard explicitly notes in Section 1.6.3 that it is acceptable to use the exact conversion or the conversion stated in the standard even though they may not be the same. This section allows for a “soft” conversion to accommodate metric products where the standard is used outside of the United States.

Whether a design is prepared using the metric system or the imperial system will typically depend on the units used in the location of the project. Whatever units are used, the use of one system or the other should be consistently used throughout the design documents.

Storage-commodity classification

The criteria for defining Class IV commodities has been expanded to include criteria for cartoned versus exposed products. Class IV commodities can also include limited amounts of Class A plastics (expanded and unexpanded). Figures have been added within the standard that note the allowable mixtures (on a percentage-by-volume basis) of expanded and unexpanded Group A plastics for purposes of defining the commodity classification (Figures (a) and (b)).

Cellulosics, natural rubber, and nylon have been reclassified from Group B to Group A plastics. Polyvinyl fluoride (PVF) has been reclassified from a Group C plastic to a Group A plastic.

Treatment of extension fittings

A definition of extension fittings (3.5.6) and criteria for their use has been added to the standard. An extension fitting is an adapter that is used to adjust the final fit where sprinklers are installed in a finished ceiling or wall. Previous editions of the standard do not address extension fittings.

A new Section 6.4.8 has been added. Extension fittings are allowed to be used with sprinklers having a K factor of 8 or less in light or ordinary hazard occupancies only. A single extension fitting having a maximum length of 2 in. is allowed, and it is not required to be included in the hydraulic calculations.

Extension fittings longer than 2 in. are allowed if specifically listed, and they are also required to be included in the hydraulic calculations.

Air venting

A requirement has been added that each wet-pipe system using metallic pipe be provided with a vent. The vent is required to be located near a high point in the system to allow air to be removed from the system (Sections 7.1.5 and 8.16.6). The vent can consist of a manual valve, an automatic vent, or other approved means. This requirement was added to provide a means for removing trapped air and oxygen that could fuel corrosion.

It is expected that the valve will be operated after each drain-and-fill event. Only one vent is required per system. There isn’t an intent that all air that may be trapped in the system be vented. The provision of more than one vent is at the designer’s discretion.

In a multistory building with floor control valves and waterflow switches on each floor, the sprinkler system serving each floor would be considered a separate system requiring an air vent.

Galvanized pipe in dry systems

The requirement that galvanized steel pipe be used in dry and preaction systems was removed from the standard. There has been significant debate as to whether galvanization of sprinkler pipe in dry and preaction systems is effective in reducing corrosion. When a breach occurs in the zinc coating of a galvanized pipe, local corrosion will occur, which can result in pinhole leaks.

A breach in the zinc coating can occur during installation or fabrication of joining methods (rolling or cutting grooves or threading pipe). GSA and the DOD prohibit the use of galvanized pipe for dry-pipe sprinkler systems.

Sprinklers under skylights

A clarifying section ( has been added to the standard regarding the placement of sprinklers under skylights. This section notes that, for the purpose of determining the distance of a sprinkler to the ceiling, the ceiling plane shall be measured to the ceiling as if the skylight were not present. This is applicable to skylights that are less than 32 sq ft in area.

It also is important to note that the 2013 and 2016 editions allow omission of sprinklers from skylights that are less than 32 sq ft in area when they are located greater than 10 ft from another unprotected skylight or ceiling pocket.

Sprinklers under obstructions

Most designers and installers are aware that obstructions that are wider than 4 ft require sprinkler protection below the obstruction. Two new criteria have been added to the standard addressing these obstructions. One requirement mandates that sprinklers be installed no more than 12 in. from the bottom of the obstruction. This is applicable to all types of sprinklers, with the exception of residential sprinklers, which are to be installed in accordance with their listed distance below ceilings (Sections,,, and

The other requirement addresses sprinklers below round ducts that create an obstruction. It requires that the sprinklers be intermediate level/rack-storage type or otherwise shielded from the discharge of overhead sprinklers. This requirement is applicable to pendant and upright sprinklers and residential sprinklers (,, and

Clearance to storage

The section allowing wall-mounted shelving that is not located directly below a sprinkler to extend above a plane that is 18 in. below the sprinklers has been revised. The 2013 edition added the allowance with language requiring the shelving to extend above the 18-in. plane below ceiling sprinkler deflectors.

The standard does not limit the height of wall-mounted shelving that is not directly below a sprinkler and does not require that it extend above the 18-in. plane. This section permits wall-mounted shelves to be placed below the 18-in. plane underneath ceiling sprinkler deflectors or above it (

Sidewall sprinklers in soffits and above cabinets

The limitation that sidewall sprinklers be located within 4 in. of the bottom of a soffit to avoid sprinklers below the soffit has been removed. The sidewall sprinkler just needs to be located on the soffit within the spacing limitations from the ceiling (

Criteria for sidewall sprinkler installations in soffits above cabinets were previously only applicable to soffits and cabinets in residential areas and occupancies. The limitation of the use of these rules in other occupancies has been deleted (

Minimum distance from obstructions

The “three times rule” to limit the impact of obstructions on water distribution requires that standard sprinklers be located a distance away from the obstruction of at least three times the width of the obstruction. The standard notes a maximum clearance of 24 in. from an obstruction.

There has been clarifying criteria added to the rule for both standard pendant and upright spray sprinklers and sidewall standard-spray sprinklers, noting that the maximum clear distance of 24 in. is not applicable when considering vertical obstructions, such as columns ( and

The “four times rule,” which is applicable to extended-coverage and residential sprinklers, also has been revised to note that the maximum clear-distance rule is not applicable to vertical obstructions, such as columns (

Small openings and concealed spaces

A new definition for small openings has been added to the standard. A small opening is defined as an opening in a ceiling or construction features of a concealed space that allows limited amounts of heat to enter the concealed space (3.3.21). The annex section notes that a 4×2-ft diffuser would meet the definition of a small opening. If the length of the opening is greater than 4 ft, the width of the opening is limited to 8 in.

Small openings come into play when determining whether a concealed space needs to be sprinkler-protected.

Bathroom sprinkler exception

Section has been revised to make the sprinkler exception for bathrooms less than 55 sq ft, that have limited-combustible or noncombustible walls, applicable to all dwelling units. In the previous edition of the code, this exception was only applicable to dwelling units in hotels and motels.

Cloud ceilings

Cloud ceilings are architectural features that are suspended below the floor assembly above. They do not form a continuous membrane as you would find in a typical drop ceiling. In noncombustible construction, the area above a typical drop ceiling creates a noncombustible concealed space that is not required to be provided with sprinkler protection. Sprinklers are required to be installed within 12 in. of the ceiling under most conditions. In spaces with a ceiling that is noncontinuous and more than 12 in. below the floor assembly above, sprinklers would be required above and below the ceiling.

A new section in the standard has been added that allows cloud ceilings to be installed without sprinklers above them. To take advantage of the allowances, an analysis must be performed that considers the elevation of the cloud ceiling, the maximum dimension of the elements of the cloud ceiling, and the gaps between cloud elements. If specific parameters are met, sprinklers can be eliminated above the cloud ceiling. Sprinkler-coverage limitations also are driven by the size of cloud elements and the space between elements relative to the cloud-ceiling height. There are also parameters on types of sprinklers that are allowed as well as the surface of the clouds (smooth-ceiling construction). These requirements and allowances are located in Section 8.15.24 of the standard.

The criteria in this section is intended to apply to a cloud ceiling that has been installed throughout a room. This section would not allow the space above obstructions suspended from a ceiling to not be sprinklered. These obstructions are often referred to as “clouds” by interior designers and architects, but due to the large openings around the clouds, would not fall within the allowances of Section 8.15.24. The maximum space between clouds or the edge of a cloud and the wall of a room is 1 in. of gap per foot of vertical height of the cloud ceiling from the floor. Therefore, a cloud ceiling that is 10 ft above the floor could have a maximum of 10 in. between clouds or between the edge of the cloud and the wall.

The minimum dimension of the individual cloud elements and the actual gap relative to the height of the ceiling is used to determine the sprinkler coverage from Table If the actual gap is larger than 1 in./ft of ceiling height, the omission of sprinklers above the cloud ceiling is not allowed.

Sprinklers in revolving doors

A code section was added to explicitly indicate that sprinklers are not required in revolving doors (8.15.25).

Sprinkler-protected glazing

Criteria has been added to address the use of sprinklers and glazing when used as an alternative to a fire-rated wall or window protection (8.15.26). This section requires sprinklers to be listed as specific-application window sprinklers unless standard-spray sprinklers are specifically allowed by the building code. This is in reference to the allowance in the IBC for the use of closely spaced standard-spray sprinklers and glass in lieu of a 1-hour separation for atrium spaces.

This section also requires that the sprinklers be on a wet-pipe system and that glazing be heat-strengthened, tempered, or glass ceramic. The water-supply duration also is required to be at least the duration of the fire resistance that is being achieved.

Inside hose stream allowance

For combination sprinkler/standpipe systems (Class I or III) in buildings that are fully sprinkler-protected, an inside hose stream demand is not required to be included in the hydraulic calculations (


Numerous clarifications in the requirements for storage occupancies have been made in Chapters 12 through 20. For those dealing with storage occupancies, review these chapters carefully.

Air-leakage testing

A new section has been added to Chapter 25 addressing air-leakage testing of modifications to existing dry-pipe and double-interlock preaction systems. Two options for testing are provided in Section One involves a 2-hour pressure test and the other method allows a 4-hour test under normal operating pressure.

Improved usability

This article highlights many of the changes between the 2013 and 2016 editions of NFPA 13. The changes that are identified are ones thought to be of most interest to current users of the standard and should not be considered inclusive of all the changes.

The 2019 edition should prove to be much improved from a usability perspective. As can be seen by how the standard has been reorganized (see sidebar), the intent is to be able to apply the document as one would go through the steps of designing or reviewing a system. As always, the standard is in a continual state of change to allow for improvement and acceptance of new technologies and approaches.