RESOURCES
CODE & STANDARD REFERENCES
- NFPA 13 – 2022: 9.5.3.2 Maximum Distance from Sprinklers to Walls (all sprinkler types)
- NFPA 13 – 2022: 9.5.3.3 Minimum Distance from Sprinklers to Walls (all sprinkler types)
- NFPA 13 – 2022: 10.2.5.2 Maximum Distance from Sprinklers to Walls (standard spray uprights & pendents)
- NFPA 13 – 2022: 10.2.5.2.3 Small Room Rule
- NFPA 13 – 2022: 3.3.40 Definition of Compartment
## TRANSCRIPT
Sprinkler-to-Wall Spacing for Stardard Spray Uprights and Pendents.
INTRODUCTION In our last segment, we looked at maximum and minimum distances for sprinkler to adjacent sprinkler. We looked at the requirements in NFPA 13 and looked at the different caveats that those rules bring with them. So, in this segment, we're moving on to the next step. Looking at the allowable distance between sprinklers and walls. There are minimums and maximums to pay attention to here as well. As a quick reminder, there are several rules that come into play with sprinkler spacing. #1 - Distance Between Sprinklers #2 - Distance Between Sprinklers and Walls #3 - Coverage Area per Sprinkler #4 – The Distance Between the Ceiling and the Roof and the Sprinkler #5 – The Distance from Sprinklers to Obstructions #6 – The Distance from Sprinklers to Heat Sources Here, let’s look specifically at number 2. Let’s look at our maximum limit first, the maximum distance from a sprinkler to a wall. SPRINKLER-TO-WALL DISTANCE Now, Chapter 9, which covers all sprinkler types and specifically section 9.5.3.2 lays this out for all sprinklers and it’s pretty straightforward. The maximum distance from a sprinkler to a wall shall not exceed half of the allowable distance between sprinklers. So how is this measured? Well, it's measured perpendicular to the wall. SPACING NEAR FURNITURE AND GLASS What if there is furniture? Furniture like portable wardrobes, lockers, cabinets, or trophy cases? Well, in those cases, in all those cases, we measure to the wall behind the furniture, not the front face of the furniture. This was actually modified in NFPA 13 in the 2022 edition to account for all furniture, not just portable wardrobes, lockers or cabinets. What about if there are windows? Do you measure to the face of the glass or the face of the wall? Well, as long as there is no additional floor space created by that window, then the measurement can just be to the face of the wall, not to the window. So even if there's a little window sill, we're still allowed to space to the face of the wall just as long as there's no additional floor space created. If the floor space is created, well, we space to the glass. ODD CORNERS Now what if we get into odd corners? What if there's some acute angular space? Now, I'll be honest, I've been waiting decades since geometry class to finally make use of the word acute. So, thanks for providing me that opportunity. To answer this, we go to chapter 10. We get a little reprieve on our half of the allowable sprinkler spacing distance rule. It's chapter 10 so this is specific to standard spray upright impendent sprinklers. But where we have in a regular or angled wall, and all points on the floor that are attributed to that sprinkler are no more than ¾ or 0.75 times the allowable sprinkler spacing distance, and the maximum distance from a sprinkler to a wall isn't exceeded when measuring perpendicular to each wall. Then the one half the allowable spacing rule doesn't apply. Here's a look at this rule in plan view with the sprinkler in red and the angled walls nearby in gray. It's essentially a pizza slice of a room where the architect had some late Friday afternoon deadline and just turned in this awful mess. Here are the limits of what the rule in NFPA 13 allows. So, it's half the distance to the wall as usual, that is measured perpendicular to each wall, so we've done that here. And the distance to the far corner cannot be more than 0.75 times the spacing. So, let's say our maximum spacing is 15 feet or 4.6 meters, that would mean this distance to the far corner cannot be more than 11.25 feet or 3.45 meters. Now let's look at an example with real measurements. Here, measuring perpendicular to the wall, our sprinkler is within half of the allowable sprinkler spacing distance, so that's good. And all points on the floor, if we measure from the furthest point in that room, all points on the floor within 0.75 times the maximum allowable sprinkler spacing. So, this sprinkler is allowed by code to cover this odd corner. Now let's cut this pizza slice like it's a kid's party. This is the project where the architect forgot about this room altogether. Here, we still meet the half the distance measurement when measuring perpendicular to each wall. But some parts of that floor area, the most remote part of the floor area is not covered by 0.75 times the maximum spacing rule. So, in this scenario, this sprinkler does not cover this corner by code. This would not be a code compliant layout. THE SMALL ROOM RULE So still thinking big picture, we're talking about maximum spacing from a sprinkler to the wall. We have one other exception in NFPA 13 that applies to Standard Spray Pendents and Pprights and it's one of my favorites, the Small Room Rule. Now for some reason, this exception is often overlooked. It seems like just about every time I lay out a system in a set of shop drawings and I use the Small Room Rule, I get some kind of review comments saying I have over space to a wall. A little education here goes a long way. So, what is the small room rule? NFPA 13 Section 10.2.5.2.3, the same section that gives us our maximum spacing distance from sprinklers to walls, states that the one-half-maximum-distance rule, that’s ½ our sprinkler spacing distance is what we’re afforded to a wall, it does not apply within small rooms as defined in 3.3.206. Under the small room rule, sprinklers are allowed to be up to 9 feet (2.7 meters) from any single (just one) wall. The sprinkler spacing limitations and area limitations still cannot be exceeded. So that's our sprinkler to sprinkler spacing and our area per sprinkler. What does that mean? It means when we have a small room that qualifies as a small room and is defined as a compartment, we'll get it in a second, that we can space to one single wall more than our 7 ½ ft (or 2.3 meters). We can space up to in that scenario, 9 feet (2.7 meters). Why does this rule exist? Well, for one, it allows the designer to better accommodate lights, diffusers, or other obstructions within small rooms that would otherwise require at least one more sprinkler. It also is acknowledging that for a small room only the sprinklers in the room should operate and they will operate at a higher operating pressure, which has a better spray pattern, it results in more flow for those fewer sprinklers. It's basically giving us just a little extra grace, a little extra tolerance to say that a small room isn't gonna fail a whole sprinkler system just because the distance to one wall is slightly over what's allowed in code. So, what is a Small Room? How do we define that? Well, NFPA 13 gives us the definition. That’s Section 3.3.206and it defines a small room as a compartment of light hazard occupancy, having unobstructed construction and having a floor area that's not over 800 square feet (74 square meters). Further, as it does come up, what is a compartment? Are we talking about a room that has to have nothing but doors and windows? Are we talking about something else? Well, a compartment is also defined in NFPA 13. And the definition is that a compartment is completely enclosed by walls and a ceiling with the only allowed openings having a lintel depth that's that space above a door or an opening of 8 inches (200 millimeters) from the ceiling, and a total width of the opening, not over 8-ft wide (2.4 meters wide). If there are no other openings, then a single opening of 36 inches (900 millimeters) is allowed. That's all it gives us from the definitions of NFPA 13. So, even if there is an opening in that room, if we've got a lentil above that opening, it's still considered a compartment and therefore it would still be defined as a small room. EXAMPLE USING THE SMALL ROOM RULE So, as an example, if we are light hazard, unobstructed, and we have a compartment that's not over 800 square feet (74 square meters), then we're allowed to space sprinklers to one single wall up to 9 feet (2.7 meters). Where do I see this come up? Offices and exam rooms. Business offices and healthcare exam rooms are often smaller sized rooms where spacing is just over what would otherwise be allowed by code. They often have lights and diffusers somewhere around the middle and these rooms repeat over and over and over so if you've got single person offices, well, those might be along an entire exterior wall of an office building or if you have healthcare exam rooms, those might repeat over and over and over and over. That's where the small room rule really comes into play. We can get a significant amount of savings, less sprinklers, less pipe to those sprinklers and all of that by using the small room rule, which just gives us a little bit more grace on the distance that's required from a sprinkler to a wall. In this example, the one we're looking at, this qualifies as a small room and a compartment under NFPA 13. So, you can see sprinklers are spaced at these distances and only to one wall are we allowed up to 9 feet (2.7 meters). And it's only because of this small room allowance. When you're saying, Joe, this doesn't look like a small room, but look at it. If you run the area on it, we're under 500 square feet for this entire room. This is light hazard, it's unobstructed. We have a suspended ceiling. So with the small room rule, this room is code compliant with the layout as it is. Without this rule, we would have to add another row of sprinklers, even though the room's relatively small. CURVED SURFACES Outside the small room rule, what about curved surfaces? I haven't run into this one myself, but you would measure at the floor level from the wall or at the intersection of the curve surface and the floor as the distance from the sprinkler to the wall. And that distance can't be more than one-half the allowable sprinklers spacing distance. MINIMUM DSTANCE TO WALL Now you mentioned a minimum distance too. What is that? 4 inches. Well, actually 4 inches (100 mm) from the nearest wall measured again perpendicular to the wall. That's pretty much all there is to the minimum. Why is there a 4 inches (100 mm) minimum distance to the wall? Well, in general, we don't want to see the spray from a sprinkler hit the wall, come back and start to affect its own spray pattern. So that's why we have a minimum distance to the wall. The only time I've seen this coming to play is with renovation when somebody builds a wall and no one moves a sprinkler and nobody's paying attention to the sprinkler. I've seen it happen then. The other cases in very small closets (and it would be a lot smaller than this one) where the ceiling space is taken up by lights and other things. In those cases, it can get pretty tight as well. But the rule is the same for standard spray sprinklers, 4 inches (100 mm) to prevent discharge from interrupting the sprinkler zone discharge pattern. SUMMARY In this segment, we focus specifically on Standard Spray Pendent and upright sprinklers. We looked at the rules that dictate minimum and maximum distances from sprinklers to walls. In general, our limit for a sprinkler to a wall is half of the allowable sprinkler spacing. These are measured to the wall, perpendicular to the wall. However, there are some exceptions. These include odd corners, curved walls, and a small room rule. In our next segment, we're gonna use these dimensions from sprinkler-to-sprinkler and from sprinkler-to-wall to get our coverage area for each sprinkler that rounds out the key trifecta, if you will, of sprinkler spacing rules in the two-dimensional plane. I’m Joe Meyer, this is MeyerFire University.
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