What are the Top 5 differences between NFPA 13, 13R and 13D?
This is somewhat of a loaded question, and the answer has changed somewhat frequently. Each code cycle introduces new changes and each of these standards, so, in a way this is an evolving answer.
Also, I'm kind of stepping out and talking about big picture generalizations here.
When we have a handbook with commentary on a standard that is over 1000 pages long, then it would be very naive of me to say that I could summarize the entire standard in a quick 4-minute video.
What I would like to address today is the big picture differences between these three standards. The only way to vet the full recourse of differences for your project is to learn and know and look up the differences for your particular project. Again, today we're looking at a very high-level big picture impacts between these three standards.
Major Difference #1: Objectives
As a starting point, each of these standards has different objectives. 13D and 13R are designed primarily with the intent for life safety, with the goal of extending the amount of time that we have to escape a burning building. NFPA 13D and R include a purpose specifically to prevent flashover in the room where the fire originates, when that room is sprinklered. NFPA 13R goes on to state that it also provides some level of property protection.
That is different than the goal of NFPA 13, which is to provide both life safety and property protection.
Major Difference #2: Limitations for Use
NFPA 13D and 13R both carry significant limitations on when they are allowed to be used.
In our last three videos we discussed this in a lot more detail, but as a short recap, 13D is intended for one and two family homes and 13R is intended for low rise residential occupancies. Both the building code and the standards themselves carry major limitations on when these are allowed to be used.
NFPA 13 does not carry these same limitations.
Major Difference #3: Allowable Code Reductions
NFPA 13 systems are more robust and offer higher levels of protection than 13R or 13D. As a result, the building code provides us some relief on other code requirements that still impact our buildings. NFPA 13 systems allow taller building heights, potentially additional stories, potentially larger buildings, reduction in occupancy separations, reduction in draft stopping requirements, reduction in requirements for manual pull stations on the fire alarm side, and a number of other benefits. Many of these benefits are exclusive to using an NFPA 13 sprinkler system.
Major difference #4: Sprinkler Omissions
There are a number of specific areas in a structure where 13D and sometimes 13R allow sprinklers to be omitted where 13 would require that protection. This is especially true in wood construction buildings which is very common for single family homes, and duplexes, and apartments, and other residential buildings. I want to talk about a few major impact areas in specific, but again be very mindful that these requirements are changing all the time. More and more we’re seeing that the building code will overrule some of these requirements out of 13, 13R, and 13D, especially when it comes to high-risk areas like attics and combustible overhangs.
So be sure to go back and reference the building code and see if it overrules any of the standards here. That's going to be at a Section 903 out of the building code if we're in the International Building Code.
Attics. NFPA 13R and 13D up through the 2019 edition allows sprinklers to be omitted within combustible attics.
There's some exceptions there and big picture. This is what we're talking about.
NFPA 13 carry some limited exceptions, but generally large combustible attics needs sprinkler protection. Attics in large open combustible spaces often require dry systems. And when they’re dry, we need steel pipe and all of the equipment associated with the dry systems. Think compressor. Think dry valve. For many projects I come across when we’re doing estimating, it's these dry systems that have the biggest cost impact when we jump from an NFPA 13R to an NFPA 13 system. Again, a new big caveat, check the building code and make sure the building code doesn't override this difference between the two standards. Recently, there have been countless number of examples of major attic fires that resulted in total building losses that were 13R buildings, so this is a sensitive and recent topic that could change very soon.
Combustible Concealed spaces. NFPA 13 has a number of exceptions for protecting concealed spaces. Perhaps the most common is for noncombustible construction or when combustible concealed spaces are filled with noncombustible insulation. If a combustible concealed space doesn't meet these stringent requirements, then the combustible concealed space under NFPA 13 will require sprinkler protection. There’s an entire catalog of lines of concealed space sprinklers that are specifically designed for this type of application. I find on many of my projects this comes into play with the floor ceiling cavities, voids above exterior soffits, within overhangs, and even combustible concealed spaces above porte cochere ceilings.
The next one is small closets. NFPA 13 requires sprinklers within closets unless the building is specifically a hotel or motel with a closet under 24 square feet or specifically a hospital with a closet that is less than six square feet. In both of these cases, the closet has to have a noncombustible surface. NFPA 13R and 13D are more generous when it comes to closets as long as the closet has a noncombustible surface and is less than 24 square feet, then 13R and 13D both have exceptions that have been in the standard up through the 2019 editions.
Closets on the exteriors require protection under 13, but 13R and 13D also have exceptions for protecting these spaces.
Finally, there's a handful of other areas where there are differences between the standards. If I'm working on a hotel where there are 300 rooms with the same setup, then sprinkler protection of a closet or a porch or a balcony could start to seriously impact the overall cost.
It's not just one sprinkler in one closet. This is 300 sprinklers in 300 closets. And that starts to add up. Some of these other areas where the standards differ are concealed spaces that include only ventilation equipment, or what I commonly hear is VTAC closets. Others are elevator machine rooms, garages, and carports, porches, and penthouse equipment rooms..
Major Difference #5: Hydraulic Calculations
Now personally, I think the differences between 13 and 13R in terms of the calculations are a bit overstated. Pipe size in an NFPA 13R system can be similar than an NFPA 13 system, but that's not always the case. Let's start with the maximum number of calculated sprinklers when we do our hydraulic calculations. NFPA 13D, the least restrictive of the three standards, only requires up to two sprinklers be calculated. There's some limitations based on ceiling heights and such, but in general most 13D calculations will involve 2 sprinklers with the density of .05 GPM per square feet.
NFPA 13R has the same density of .05 GPM per square feet, but the calculation steps up to calculate as many sprinklers are in a compartment up to four sprinklers.
Lastly, using residential type sprinklers in an NFPA 13 system, the calculation will involve 4 adjacent sprinklers at a .10 GPM per square foot density for new buildings. Existing buildings are allowed to use the listed values for the sprinklers, so that density could be lower. NFPA 13 also requires a hose allowance, but we can add that at the riser or the street and doesn't have to impact the pipe size inside the building.
Some contractors I've spoken with about the hydraulic calculations, they make it out to be a huge difference in cost. And I can see that in some cases. But if we're comparing CPDC systems with larger compartments or larger rooms within the building, then an NFPA 13R in an NFPA 13 calculation could end up looking fairly similar. We’ll get into this in more detail later, but just keep in mind that a .05 and a .10 density is the minimum required density for the sprinkler across its coverage area. If a sprinkler requires a minimum pressure in order to achieve some larger spacing, then the minimum pressure may actually be the driver for the sprinkler and not the density. Both the minimum pressure on the listing of the sprinkler and the density have to be considered in the calc because it's the higher of the two that is applied in our hydraulic calculation. Sometimes, the sprinkler pressure will be the driver and sometimes the density will be the driver.
Just as a quick example, I recently had an NFPA 13R project where I was using residential sprinklers and trying to keep the overall flow down. The listing of a K 4.9 sprinkler required a 7 PSI minimum pressure just to use its 14 foot by 14 foot spacing. Based on my compartment size and the way the sprinklers laid out, I was actually achieving a density of .13 GPM per square foot at my remote area even though 13R only requires a .05 GPM per square foot density. In this case, being that I was calculating four sprinklers, and NFPA 13 and a 13R calculation would have looked exactly the same. That won't always be the case, but it's just important to begin to understand that just because the density in 13 is twice that of 13R, doesn't mean the results are gonna be dramatically different. It depends really on the project and the layout of the rooms, layout of the sprinklers, and how that configuration ends up.
To recap, our major differences are different goals of the standards, that they have different limitations for when they can even be used, that they have different code allowances for the rest of the structure, that they have different areas where sprinklers can be omitted, and the hydraulic calculations are different from a high-level overview. These are my top 5 differences between the three standards, NFPA 13, 13R and 13D.
I'm Joe Meyer, this is MeyerFire University.
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