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Sprinkler Systems in Mixed-Use Buildings

Monday, December 22, 2014

By CAD Designer, Ahern Fire Protection

Downtown metro space is becoming more and more valuable. Because of this, many buildings are being built for more than one purpose, making them non-traditional when it comes to design. This added challenge can result in costs being much higher than they need to be in order to design and build the building. An important part of buildings is the automatic sprinkler system, which may be a small portion of the budget, but if it is not accounted for, could result in significant costs. This article will cover how to effectively design a building so that it meets fire code, but is also cost effective.

Mixed-Use Buildings

Many downtown metro areas have mixed-use buildings, which are used for more than one purpose -- such as a building with a parking garage in the basement, a retail or restaurant on the ground level, and apartments or offices on the upper floors. Even many small towns have old main street buildings that have been restored to have a business at street level with apartments above. 

Mixed-use buildings have special challenges for the design of an automatic sprinkler system in them. The spaces with different uses may require different sprinkler types and spacing based on occupancy. The International Building Code (IBC) gives many guidelines for mixed occupancy buildings in section 302.3. The code allows the spaces to be individually categorized by level of hazards and then the entire building is designed based on the most restrictive provisions. The building does not require any additional fire separations except where they are specified elsewhere. A fire separation is a wall or floor which is designed to stop the spread of fire to adjacent spaces for a certain period of time allowing occupants to escape to safety.  The other option is to use code 302.3.3 by separating the different classifications with fire separations so that different parts of the building can be designed like they are separate buildings.

NFPA 13

To understand why mixed-use buildings are potentially problematic, it is first important to understand the basics of how sprinkler systems are designed for buildings. The code that dictates the installation and design of sprinklers is the National Fire Protection Association 13 (NFPA 13). This code gives guidelines for the spacing of sprinklers and how much water they must provide to the building. NFPA 13 has different occupancy classifications based on the quantity and combustibility of the materials that are in the protected space. Light hazard, the least restrictive occupancy rating is used for buildings with conditions similar to churches, schools, and offices. The next level of occupancy is ordinary hazard which is broken down into two groups. Ordinary hazard group 1 is for areas where combustibility of materials is low, but the quantity of combustibles is moderate. An example of an ordinary hazard group 1 includes restaurant serving areas, bakeries, and car parking areas. The higher classifications, ordinary group 2 and extra hazard group 1 and 2 are the next levels of hazard in fire ratings, each one is the next step based on the amounts of heat that could potentially be given off in the given area.  These classifications are important because they dictate how close the sprinklers need to be along with the amount of water that will be demanded. While the material costs of the sprinkler heads might not be as significant in the big picture, it does mean that the pipes feeding the sprinkler heads will need to be larger to meet to water flow and pressure requirements, thus driving up costs. This will also drive up labor costs with the additional time to install and trim out the extra sprinkler heads and the larger pipe which is heavy and increasingly difficult to work with.

NFPA 13R is the residential version of NFPA 13 for residential occupancies up to and including 4 stories high. This code was designed to prevent flashover in the room where the fire originated according to the results of full scale testing performed with typical bedroom and living room furniture layouts. Flashover is the point where the temperature is so hot (around 930°F) that everything in the space will ignite. NFPA 13R is less restrictive than NFPA 13, typically requiring less sprinklers in a space and sometimes not requiring sprinklers in certain bathrooms, closets, and attics. One major area where sprinklers may be omitted is in combustible concealed space that is often formed above ceilings. NFPA 13 requires combustible concealed spaces to be sprinkled unless special requirements such as being filled with insulation and fire separations. Combustible concealed space that would need sprinkler protection above the ceilings could essentially double the amount of sprinkler heads in a building. NFPA 13R does not have this requirement with the concealed space which could have a huge cost savings for the owner. So it is desirable, if allowed, to classify a space as NFPA 13R instead using the light hazard requirements from NFPA 13. When 13R is used in a design it must be used throughout the entire building. NFPA 13R is focused more on controlling the fire to provide life safety and not concerned about saving the property.

Building Design

NFPA 13 is required to be used in buildings that have any portion that is to be used for the general public and residential occupants. NFPA 13R is for buildings that are for residential use. This means that if there is a lounge or a fitness room the ground floor, but is only limited to the residents use and not open to the public, then the building can be designed under NFPA 13R. The 13R code also clarifies that it if part of the building contains a non-residential occupancy but is incidental to the operations of the building, then 13R can still be used. This rule still seems vague, so a way to determine if it is incidental is by profit. If the non-residential portion (a store for example) is there because it gets most of its business from the building occupants, then it is incidental to the use of the building. On the other hand, if the store is fully capable of operating with limited profits from the residents of the building and instead makes its profit from the public, then it is not incidental to the use of the building – meaning that the entire building will need to be designed per NFPA 13. But, if the building is made with fire separations between the non-incidental/ non-residential portion and the residential portion of the building, each portion can be considered a separate building. This allows the residential portion of the building to be designed per NFPA 13R and only the additional spaces to be designed under NFPA 13. Depending on the building construction and the uses of the spaces, this fire separation may be required to be a fire wall, which is a vertical fire separation that has independent structures on either side that need to be able to stand on their own for the rated duration of the fire wall.

Whether or not to use the fire separations should be decided early in the design of the building.  The financial impact could be considerable because a fire separation would impact all trades involved in the project but could reduce the sprinkler system cost. The separation would require penetrations through it to be minimal and each penetration to be protected to maintain its rating. On the other hand if the building is designed so that the sprinkler system is very large, it will also cause problems to the other trades. Pipe and sprinkler heads will be more difficult to avoid and will take up space that is often needed for ductwork or plumbing. Every building is different and each one requires its own special consideration.

To conclude, mixed-use buildings are all unique, need to follow NFPA and need to use carefully planned designs to make them cost effective for the owner. Mixed use buildings could have a lot of potential problems that come up during construction and design if things like the fire sprinkler system are ignored until later on. It is important to get the sprinkler contractor on-board with the project early to help with the costs associated with the building’s design and to point out potential cost savings. This article does not focus on how sprinklers may affect a specific building, but should help with knowing what questions to start asking early on, when involved in a project with a mixed-use building.

Want more information? Contact Ahern directly!

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