Sprinkler installations and obstructions

Sprinkler protection is an essential component of building fire and life safety. Sprinkler fire suppression systems are required to be installed with an understanding of the applicable standards and proper coordination among other building services throughout a project lifecycle.

By Roy Savio Fernandes, SFPE, Jensen Hughes, Dubai, United Arab Emirates April 18, 2019

Learning Objectives

  • Learn about the different types of sprinklers used in building and life safety protection.
  • Understand various obstructions to sprinkler-discharge patterns.
  • Follow correct measures to mitigate or eliminate obstructions and ensure complete sprinkler coverage.

Automatic sprinkler systems offer a level of minimum protection required by international building codes and standards, such as NFPA 5000: Building Construction and Safety Code and International Building Code (IBC)Shop drawings, installation drawings, and floor plans provide the contractor necessary guidelines on the location, spacing, and height of sprinkler deflectors 

If everything is installed according to the fire protection engineer’s specificationsthere should not be any problems, one may be led to think. However, every project site brings new challenges during sprinkler installation. Proper supervision and coordination are essential to get the installation done correctly. Even though the best efforts may have been put forward, one still comes across areas where installed sprinklers just don’t seem correct. 

Typically, one of the main areas of concern has beenand probably will continue to belarge mechanical rooms. Such rooms are found with HVAC ducts greater than 4 ft wideMore often, sprinkler coverage is found only above such large ducts, with no sprinkler coverage below the ducts 

NFPA 13-2016: Standard for the Installation of Sprinkler Systems, Chapter 8, requires additional sprinkler protection below fixed obstructions (such as cable trays and large ducts) exceeding 4 ft wide that prevent sprinkler-discharge from reaching the hazard. In accordance with NFPA 13, Section, sprinklers shall be located below the obstruction, not more than 3 infrom the outside edge of the obstruction, and within 12 in. from the bottom of the obstruction.  

However, NFPA 13 also provides certain exemptions where sprinkler protection would not be required below obstructions exceeding 4 ft wide. These may include noncombustible fixed obstructions where the bottom of the obstruction is 24 in. or less above the floor level or obstructions that are not fixed in place, such as conference tables 

Another area of exclusion by NFPA 13, Section, for sprinkler protection below such largobstructions is if the room(s) being protected is (are) not larger than 400 ft3. In such cases, sprinkler protection will only be required at the highest ceiling level.  

Lastly, there is no requirement for sprinklers below ducts if the size of the obstruction is up to 4 ft wide and located more than 18 in. below the sprinkler deflector. In this event, an adequate spray pattern develops; there is no need for additional sprinkler protection underneath. 

If the obstruction does not exceed 4 ft wide, standard pendant- and uprightspray sprinklers shall be permitted to be spaced on opposite sides of such obstructions, provided the distance from the centerline of the obstruction to the sprinklers does not exceed one-half of the allowable distance permitted between sprinklers. 

Sprinklers and obstructions

The question then arises, do we need sprinklers above such obstructions as well? We often find no sprinkler protection or coverage above such large obstructions where sprinklers have been provided below. To comply with NFPA 13, sprinklers are required above the obstruction at a distance not less than 1 in. and not more than 12 in. from the ceiling above, assuming unobstructed construction. 

Sprinkler obstructionalso are commonly found in storage rooms. Such rooms usually contain stacks of goods (pallets, merchandise) placed below the sprinkler deflectors, which may prevent the sprinkler spray pattern from reaching the hazard 

  • If goods are stacked up to within 18 in. or less directly below the sprinkler deflector, then the stacked goods are required to be reduced in storage height to a distance greater than 18 in. from the sprinkler deflector. 
  • Where shelving is installed on a wall and is not directly below sprinklers, the shelves, including storage thereon, shall be permitted to extend above the level of a place located 18 in. below the ceiling’s sprinkler deflectors 

If the obstruction in such storage rooms is not portable (such as pipes, columns, or fixtures), the sprinkler deflector is required to be repositioned away from the obstruction. NFPA 13, Chapter 8, Sections 8.6 through 8.12, provide additional guidelines that include minimum clearances required to be maintained from such obstructions.  

Besides storage rooms, for any area where continuous sprinkler obstructions are located less than or equal to 18 in. below the standard pendant and upright spray sprinkler deflector, clearances are determined based on the depth of the obstruction (as defined in NFPA 13, Table To elaborate: 

  • An obstruction height of around 3.5 in. between the deflector and bottom of obstruction is required to have sprinkler installed at a minimum of 18 in. and maximum of 24 in. from the side of the obstruction.  
  • An obstruction of around 12 in. between the deflector and bottom of obstruction is required to have a sprinkler installed at a minimum of 3.5 ft and maximum of 4 ft from the side of the obstruction. 

Let’s now take a brief look at couple of obstruction types located against the wall and how they impact standard pendant and upright spray-sprinkler coverage.  

Obstructions located against the wall that are no more than 30 in. wide shall be protected in accordance with NFPA 13, Chapter 8, Section 8.6.5 (see Figure 3): 

A: The horizontal distance from the side of the obstruction. 

B: The spacing from the bottom of the obstruction to the sprinkler deflector. 

D: The width of the obstruction. 

Obstructions located against the wall that are not more than 24 in. wide shall be protected in accordance with Chapter 8, Section 8.6.5. The maximum distance between the sprinkler and the wall shall be measured from the sprinkler to the wall behind the obstruction and not to the face of the obstruction. 


Another concern is ceiling patterns, such as ceilingbeam drops, sidewall projections, and soffits, that may cause sprinkler obstruction. NFPA 13, Chapter 8, provides guidance and required distances based on the size of the side obstruction and the horizontal distance from the obstruction to ensure adequate sprinkler coverage throughout the space being protected. 

Installing upright spray-sprinklers too close to (or touching) the ceiling level is another common occurrence that can negatively impact the sprinklers’ coverage pattern. Standard pendant and upright spray-sprinklers shall be required to be installed at a minimum of 1 in. and a maximum of 12 in. from the unobstructed ceiling above. The only exception to this rule is where ceiling-type sprinklerssuch as concealed, recessed, and flush typeshave the operating element above the ceiling and the deflector located nearer to the ceiling. These sprinkler types are required to be installed by their corresponding listing. 

In ceiling areas containing skylights, sprinklers shall be permitted to be omitted from skylights not exceeding 32 sq ft in arearegardless of hazard or classificationthat are separated by at least 10 ft horizontally from any other unprotected skylight or unprotected ceiling pocket. When a sprinkler is installed directly beneath a skylight not exceeding 32 sq ft, the distance to the ceiling shall be measured to the plane of the ceiling as if the skylight was not present. 

In areas of unobstructed ceiling construction, where a vertical change in ceiling elevation within the area of sprinkler coverage creates a distance of more than 3 ft between the upper ceiling and the sprinkler deflector, the vertical plane extending down from the ceiling at the change in elevation shall be considered a wall. Sprinklers shall then be spaced accordingly. 

For peaked roofs, sprinklers at the highest elevation shall not exceed a distance of 3 ft, measured vertically down from the peak as defined in NFPA 13, Section 8.6.4. Deflectors of sprinklers shall be aligned parallel to ceilings, roofs, or the incline of stairs. However, where sprinklers are installed in the peak below a sloped ceiling or roof surface, the sprinkler shall be installed with the deflector horizontal. Roofs having a pitch not exceeding 2:12 (16.7%) are considered horizontal, and sprinklers shall be permitted to be installed with deflectors horizontal. 

Once again, NFPA 13 provides exemptions to obstructions caused by ceiling construction types, most notably those with ceiling pockets. Exemptions for those with ceiling pockets are allowed if all of the below are met:  

  • The total volume of the unprotected ceiling pocket does not exceed 1,000 ft3. 
  • The depth of the unprotected ceiling pocket does not exceed 3 ft. 
  • The entire floor under the unprotected ceiling pocket is protected by sprinklers at the lower ceiling elevation. 
  • The total size of all unprotected ceiling pockets in the same compartment within 10 ft of each other does not exceed 1,000 ft3. 
  • The unprotected ceiling pocket has noncombustible or limitedcombustible finishes.
  • Quick-response sprinklers are used throughout the compartment. 

Lighting and emergency lighting

Emergency and exit lights serve as a vital part of building egress. Care must be taken when installing such lighting fixtures in proximity with a sprinkler deflector. Sprinklers are required to be installed away from lighting fixtures, in the horizontal orientation, at a minimum of three times the width of the side of the obstructionand up to a maximum of 24 in. away from the side of the obstruction in extra hazard occupancies. 

In light and ordinary hazard occupancies, sprinklers shall be permitted to be spaced on opposite sides of the obstruction. The distance from the centerline of the obstruction to the sprinklers must not exceed one-half the allowable distance between sprinklers, as defined in NFPA 13, Section 8.6.5 

Another type of commonly used sprinkler is the horizontal sidewall sprinkler. Due to the nature of the project site conditions and ceiling construction, sidewall sprinklers are more preferable at times in lieu of pendanttype or upright spray-sprinklers. It is important to ensure that horizontal sidewall sprinkler deflectors shall be located 6 to 12 in. or 12 to 18 in. below noncombustible and limited-combustible ceilings, respectively, where listed for such use. 

On certain occasions and for a more artistic look and finish of the areas being protected, soffits are constructed on ceilings where sidewall sprinklers are used. This aesthetic finish stands out and appears striking; however, it could also cause an obstruction to the sidewall sprinkler’s discharge pattern. If the soffits exceed more than 8 in. wide or project from the wall, pendant sprinklers shall be installed under the soffit in accordance with NFPA 13, Section 

In addition, sidewall sprinklers shall be located no closer than 4 ft from light fixtures or similar obstructions. The distances between light fixtures or similar obstructions located more than 4 ft from the sprinkler shall follow minimum clearances as described in Table of NFPA 13:  

If the distance between the obstruction and the bottom of the horizontal sidewall sprinkler is up to 4 in., then the minimum distance of 6 ft and maximum distance of 6.6 ft is required to be maintained between the sprinkler and the obstruction as described in Table of NFPA 13. 

Sidewall sprinklers also shall be located under fixed obstructions more than 4 ft wide; however, sprinklers shall not be required under obstructions that are not fixed in place, such as large conference tables. Sprinklers also shall be permitted to be spaced on opposite sides of an obstruction that is less than 4 ft wide, where the distance from the centerline of the obstruction to the sprinklers does not exceed one-half the allowable distance between sprinklers. Obstructions on the wall opposite from the sidewall sprinkler shall be permitted where the obstruction is up to 24 in. deep and 24 in. wide. 

Obstructions projecting from the same wall as the one on which the sidewall sprinkler is installed shall be in accordance with NFPA 13, Table To elaborate on the table provided in the standard: 

  • If the distance of deflector above bottom of obstruction is 1 in., it is required to have sidewall sprinkler installed at a minimum of 4 in. and maximum of 6 in. from the side of the obstruction.  
  • If the distance of deflector above bottom of obstruction is 10 in., it is required to have a sidewall sprinkler installed at a minimum of 4 ft and maximum of 4.5 ft from the side of the obstruction. 

Meeting manufacturer instructions

The fundamental principle of any fire suppression device or system is that it shall be installed in accordance with its listing or published manufacturer instructions. However, despite the best efforts of the entire project team, errors occur. Sprinkler piping is installed to follow the ceiling pattern, which may include large ceiling pockets, high-rise ceiling sections, or sloped ceilings. Depending on the type of the ceiling pattern, contractors install either pendanttype or upright spray-sprinklers. Pendantmount sprinklers are listed as pendantmount only, and upright spray-sprinklers are listed for uprightmounted installations onlyAn installation of a pendantmounttype sprinkler deflector in an upright manner, and vice versa, is in noncompliance with NFPA 13, Section 8.3.1 

Similarly, concealed sprinklers and their associated escutcheon plates form a listed assembly. Installations of sprinklers without their escutcheon plate or of concealed sprinklers in lieu of pendanttype sprinklers by removing the escutcheon plate are noncompliant with NFPA 13. Concealed sprinklers are not listed to be installed in openceiling areas. 

Rather than installing sprinklers and creating sprinkler obstructions, NFPA 13, Section 8.15, allows for sprinklers to be omitted in special situations, which include: 

  • Concealed spaces of noncombustible and limitedcombustible construction, with minimal combustible loading, having no access or not permitting occupancy or storage of combustiblesExamples include spaces used as return air for plenums and spaces with minor quantities of cabling or nonmetallic plumbing piping. 
  • Concealed spaces filled with noncombustible insulation shall not require sprinkler protection with a maximum of 2 in. air gap at the top of the space. 
  • Concealed spaces over isolated small compartments not exceeding 55 sq ft in area. 
  • Noncombustible or limitedcombustible, inaccessible vertical duct shafts, vertical electrical or mechanical shafts.
  • In noncombustible stair shafts beneath the first accessible landing and above the bottom of the shaft, if the space under the stair is blocked off so that storage cannot occur. 

Caution and precision are required when installing sprinklers to avoid some of the common obstructions described herein, or additional sprinklers shall be provided to ensure adequate coverage of the hazard. The purpose of sprinklers is to provide a level of safety both tbuilding occupants and to the building itself. Good practice, code and standard compliance, and attention to detail are the building blocks for a safe and sustainable environment provided through sprinkler protection. 

Author Bio: Roy Savio Fernandes is project director at the Jensen Hughes Dubai office. Prior to this position, he worked for several manufacturing companies.