(This discussion is based on the laws of the Commonwealth of Massachusetts, but applies to most other parts of the country as well.  Please check the code(s) in effect your region before relying on or using this information).

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SPRINKLERS SYSTEMS FOR RESIDENTIAL BUILDINGS

Whether or not a sprinkler system is required is usually determined early in the design of a building.  A code book is opened, an architect or engineer flips to the appropriate chapter, and a decision is made.  Sprinklers are required because of the nature of the occupancy, the size of the building, the number of people expected to occupy it, and/or for other reasons.  The determination is usually straightforward.

Another one of the first steps in the design of a building is determining how large it will be.  Based on the type of construction and the use group (i.e. occupancy) classification, limits for the maximum allowable area and height are provided in a table in the building code.  For the most part, stronger, more fire-resistant structures and use groups with lesser potential for loss of life are allowed to be built larger and taller.

For most use groups, the maximum area and height are allowed to be increased if certain other "features" are incorporated into the design of the building.  One such adjustment has to do with whether or not the building has an automatic sprinkler system.

If you are an architect, or you hire architects to do work for you, chances are you've utilized sprinkler systems so that you can make your buildings larger and taller.  In our experience, the biggest mistake that architects make is assuming that all sprinkler systems are created equal.  

There are essentially two types of sprinkler systems - residential systems, and non-residential systems.  The building code allows residential systems to be used in residential buildings if certain criteria are met.  The most important point of this discussion is to emphasize the fact that BUILDINGS CANNOT BE MADE LARGER (I.E. AREAS CANNOT BE INCREASED BEYOND THE LIMITS IN THE AFOREMENTIONED TABLES) WHEN A RESIDENTIAL SPRINKLER SYSTEM IS UTILIZED.  The building code is very clear on this point, yet it is very often overlooked.    

For the purposes of this discussion, residential sprinkler systems are  those that are designed in accordance with NFPA 13R, "Standard for the Installation of Sprinkler Systems in Residential Occupancies up to and Including Four Stories in Height".  What you may or may not realize is that there are important differences between systems that are designed in accordance with NFPA 13R and those that are designed in accordance with NFPA 13 (less the "R"), "Standard for the Installation of Sprinkler Systems".  NFPA 13 (less the "R") covers the installation of sprinkler systems in MOST types of buildings.  NFPA 13R covers the installation of sprinkler systems ONLY in residential buildings up to and including four stories in height.

NFPA 13R was introduced in 1989 in an attempt to provide an economical solution to the growing problem of fire-related deaths in the home.   NFPA 13R systems are aimed more at saving lives than protecting property.   Although NFPA 13R systems inherently provide a certain level of property protection, they are not intended to save the building.  They are intended to allow occupants sufficient time to escape.  

The biggest advantage of NFPA 13R is that it allows a weaker water supply.  In many cases where an NFPA 13 (less the "R") system would require a strong city water supply or an expensive fire pump, an NFPA 13R system is achievable without either.  NFPA 13R also allows the omission of sprinklers from attics and certain bathrooms and closets.  Fewer sprinklers means lower cost, and attics in particular can get very expensive to protect because special measures need to be taken to prevent water-filled piping from freezing.  The omission of sprinklers from these areas acknowledges statistics that show a low loss of life in situations where fires start there.  That's not to say that fires don't start in these areas - indeed they do.  And without sprinklers, fires that start in these areas can grow and cause major and/or complete destruction.

If you take one thing away from this article, let it be this - you need to know what TYPE of sprinkler system is being installed in your building.  If you are building a residential building, you very well may be given (or desire) an NFPA 13R system.  If the system is to be designed in accordance with NFPA 13 (less the "R"), then you needn't be so concerned about the "increases" or building code "exceptions" you or your architect are taking.   Don't get caught making your building larger with an NFPA 13R system though.  We all know it is much more expensive to go back and fix problems later.

An important fact to note is that under some circumstances, a residential building CAN be made one story higher when a NFPA 13R system is utilized (at least in Massachusetts).  There are specific requirements and it is important to be aware of and understand these requirements.  Again, in NO circumstance can the area of a building be increased when an NFPA 13R system is utilized.

The effect of using an NFPA 13R system goes beyond the size of the building.  While this article will not cover the additional implications in detail, it will mention a few topics that professionals in the State of Massachusetts should note for further review.  This list identifies some, but not all requirements that are "relaxed" when you utilize an NFPA 13 system, but not if you utilize an NFPA 13R system.  These include:

    *  No reduction in required separation between use groups

    *  No decrease in fire resistance rating of non-loading bearing exterior walls and no increase in maximum area of exterior wall openings

    *  No omission of fire dampers where ducts pass through one-hour fire rated walls

    *  No reduction in dwelling unit separations (unless sprinklers are installed in all closets that border tenant separation walls AND in all bathrooms)

    *  No relaxation of requirements for accessible means of egress components such as exterior stairs and elevators

    *  Special auto-unlocking of doors in means of egress not allowed (i.e. all egress doors must remain unlocked at all times)

This list should not be considered exhaustive, but rather as an indicator that there are several areas where the use of an NFPA 13R system may create issues.

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Should you have any additional questions regarding residential sprinkler systems please contact us.  We can provide substantiation for the statements made in the previous paragraphs by providing excerpts from the Massachusetts Building Code.