Best Way To Lay Out Sprinklers in OH Space?

7/2/2019

I'm a learning sprinkler designer and I have a question that's more about design efficiency.

When you lay out sprinklers in large Ordinary Hazard areas (assuming there's ceilings or unobstructed construction), what is the first step you take to drop sprinklers in the space?

Do you calculate the area of the room and then determine, at a minimum, how many sprinklers you need? Do you use drafting tools to automatically optimize the layout? Do you have circles around the sprinklers for approximate coverage and repeatedly shift until you like the layout?

I typically start with the area of the room and divide by 130 to determine the minimum quantity of sprinklers, then dimension each wall to start with an "optimum" spacing. I feel like this takes longer than it should, so I'm curious if there's a better approach I could be using. Any help is appreciated.

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8 Comments

Wayne Ammons

7/2/2019 08:02:23 am

This question sent my brain into overdrive as if I were sitting down with a new designer for his very first day of training. It sounds like you already have an understanding of the basics of sprinkler spacing requirements so I’ll skip to just a few thoughts on how I begin to layout a large room.

Let’s assume a large ordinary hazard room with 2’x2’ acoustical ceiling tile and basic “obstructions” to stay away from, i.e. lay-in lights, mechanical diffusers, etc. Let’s also assume your sprinklers must be located in the center of lay-in ceiling tiles and so your maximum sprinkler spacing will be 10’ x 12’ (120 sq.ft.).

One of the first things I consider is optimizing my branch line spacing. Determine the direction the structure is running and that typically determines the direction your branch lines will run. This will be your 12’ spacing between sprinklers. Next, I locate the first sprinkler in one corner of the room in the center of a tile that will be a maximum of 6’ from one wall and 5’ from the other (the half spacing rule). I visualize which tile makes the most sense to start in to miss all of the obstructions while maximizing the 10’ x 12’ spacing between sprinklers throughout the room.

This is a very simple analogy but I use this beginning thought process to get going on nearly every project, be it an office building with ceilings or a warehouse with exposed structure. Depending on the drafting program you use, there are tools that will aid you in visualizing sprinkler spacing by drawing different sized boxes around sprinklers as you insert them, or you could draw your own squares or circles to fit your specific spacing requirements. There’s the mathematical method in spacing sprinklers, which you described in your post, then there’s the practical method that considers many factors that are project specific to create the most efficient layout possible. My recommendation is to practice sprinkler layouts and review them with an experienced designer that can help you through all of the nuances of sprinkler spacing and layout. With experience, you’ll be able to visualize your layout without placing the first sprinkler all while considering spacing requirements, obstructions, hydraulics, etc. I hope this response was somewhat helpful, feel free to ask if you have additional questions. Good luck!

On the Clock

7/2/2019 10:29:52 am

Gotta be quick, but excellent points, Wayne, your design trainee is fortunate to have you. While sprinkler layout is the starting point, part of the skills one needs to eventually develop is taking into account several factors, and eventually, understanding costs. And frankly, befriend and listen to the experienced fitters. A few extra sprinklers is cheaper than an additional branch line, mains are more expensive than branch lines, etc. Of course these are over-simplified generalizations, and perhaps jumping ahead a bit for a beginning designer. Taking into account the structure, obstructions to routing the piping, HVAC, lighting layout, fabrication methods (threaded vs. grooved, pipe lengths), ease of installation, are just as important as sprinkler spacing. Aesthetics and symmetry somewhere further down on the list, depending on the project. And for sprinkler layout, it’s more squares and rectangles, not circles as in lawn sprinklers. Good question.

7/2/2019 11:41:31 am

...Oh, and if sprinklers are required above the ceiling because it's a combustible concealed space, or AHJ requirements, that may influence the methodology of spacing of the sprinklers below.

Michael

7/2/2019 12:23:09 pm

If you design it 12 foot between lines you might be able to eliminate a line or 2.

pjd

7/2/2019 10:40:12 am

I was in your shoes not terribly long ago. Good question!

So, to partially echo Wayne above, just consider that you will very seldom achieve a maxed out spacing. Even if you did, the closer to max spacing you end up, the less flexibility in the design you will have to move sprinklers where there are conflicts.

I use a temporary layer and extend lines from the inside face of the walls. Take into account that lately pipe is more expensive than sprinklers are. So, more space between lines and less space between sprinklers is ideal. Branch lines will run perpendicular to the joists/perlins. Then you will have beams or girders with columns that support the joists running parallel to the branch lines. Look at that distance between bays. If it is 50 feet or some multiple of 25, you will likely have 12-6 between branch lines, splitting the column line with a line 6-3 off of either side. If it is 30 foot bay spaces, 15'-0 between branch lines. That is maxed out for Ordinary hazard, and so your spacing down the line is limited by that to 8-8, 130/15.

After I figure out what my spacing is, I use an Offset command to make a grid with the temporary lines, then I copy a sprinkler symbol block to the intersections of a single line, then copy the line across the entire drawing.

Jake

7/2/2019 12:35:58 pm

To echo some of the previous replies, some of the software used for sprinkler design have built-in tools for head layout. I know HydraCAD has a custom tool that shows a square (or rectangle) outline around the head you are inserting so that you know where each head can be spaced to. AutoSPRINK has multiple tools to quickly layout heads efficiently. If you are using an actual sprinkler design software get familiar with every tool that it offers. When I was first starting out my colleagues were surprised at how fast I was with layout just by getting to know the software.

Karthik india

7/2/2019 02:19:45 pm

When you lay out sprinklers in large Ordinary Hazard areas (assuming there's ceilings or unobstructed construction), what is the first step you take to drop sprinklers in the space -

- answer for these it depends on your layout you draw,some of the following steps to keep in mind.
1. We have to co ordinate with other traders
2.spacing of sprinkler not more than s/2 distance
3.if ceiling is gypsum (based on spacing)or 2x2 tile (center to tile)or 4x2 (1/4 or 3/4 tile)r even I have 4x4 tile (center)
4.mainly coverage 110 to 125sqft don't space always to maximum of 130sqft. If other trades or service changes we have to provide additionally for addendum.
5.usually by practice you can get the spacing to find the best way for different projects.
6.learn NFPA obstruction rules or specification given by client
7.Am using sprinkcad software for placing heads
8.Even u can't provide head drops underneath of bigger ducts in worst case of space available between duct & ceiling, you can go with flexible droppers but to tidy to run the pipe.
9.avoid shadow area of sprinkler coverage for designing OH
10. while designing it's should not be under coverage or over coverage.

J Rob

7/5/2019 11:13:04 am

I always start in the middle of the room and lay out the heads towards the walls. Once the last heads are laid out I can shift the whole row and add one if needed. Then its copy the row and repeat in the other direction. There's always a little tweaking but 90% is done and it's pretty quick.

Best Way To Lay Out Sprinklers in OH Space?

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