NFPA 13 Requirement for Hyd. Calc. on Renos?

[Jeremiah187]

Has anyone gotten specific. data from NFPA or AHJ's with regards to at what point during a renovation does an existing hydraulic calc'd system require a new hydraulic calculation performed.

Existing pipe schedule system can have pipe schedule done on reno's up to 5000ft2.

I've looked through NFPA 13 2007 and have not found sepcific information on the subject. I believe it is a grey area.

And as usual the decision rests with the AHJ.

The problem arises when you do recalc. and get a lesser flow test then the original calcs performed. Is it owners responsibility to upgrade entire system to work under new flow test?

I would like an NFPA 13 code specific item to show the governments Technical Services people that the addition of one head tied into a 3" main does not require a new Calc?

Cheers to anyone with any ideas!

 

[cdafd]

Have you asked them to provide you with a section of 13 or local requirement that it does need to be done???

could see if there was a change of hazard, but not adding one head

there is 14.4.1.1 and A 14.4.1.1 nfpa 13 2002 but it seems to say calc it

I thought I saw something the other day in 13 about existing hydraulic systems and now can not find it.

 

[SprinklerDesigner2]

Depends.

I had a job once where we were adding two stinking sprinklers in a vestibule and I was required to provide a complete set of drawings showing the entire existing system with calculations.

As for AHJ's I've found the more knowledgeable they are the less they require.

 

[Jeremiah187]

"Depends" seems to be the going answer. Just out of curiosity what part of north America are you working in just for shits and giggles?

Our Local AHJ is letting experienced Sprinkler Contractors tell them, whether or not they feel a new Calc. is required. I find this may be a little biased.

Seems the local AHJ does not like taking the risk of saying yes or no. hahaha

 

[cdafd]

never mind, finally saw what I read the other day and took it out of context. Looks like they can ask for calcs

we require plans over 20 heads, put have not had a large redesign where it looked like clacs would be required, mainly adds and relocates

Like I said if there appeared change of hazard or large addition to system could see requireing it

 

[SprinklerDesigner2]

eremiah187,

I work in South Georgia moving here from Ohio/Michigan several years ago where I worked both those states and surrounding. Moved mostly due to weather and a bureacracy that is out of control.

 

[PEDARRIN2]

It is doubtful that adding a couple sprinklers would affect much. But as an engineer, I would like to at least have the zone affected recalced - just to make sure that nothing has changed since the original design was installed.

With development of areas and more loads being placed on water mains, it could be an issue.

Now, I don't think the owner should necessarily have to redo his sprinkler piping/system if there is a pressure problem, but at least it raises a red flag that there is an issue.

If needed, the sprinkler contractor who does the calc can use lower pressures/flows at his sprinklers (still remaining above the minimum)or change out some piping in the zone and get the hydraulic calcs to be acceptable. I have seen that with new construction when there is a tight pressure requirement.

 

[SprinklerDesigner2]

PEDARRIN2,

I agree and I'll make a bold statement that any certified sprinkler tech should be able to determine if calculations are needed in just a few minutes.

A store has a grid system, 4" mains 1 12" lines, and is going to be adding an entry vestibule requiring two additional sprinklers. If the vestibule is located on the side of the grid with the heads fed from one of the mains I can't conceive of a hydraulic calculation situation that the two additional sprinklers can cause.

If the vestibule is located at the end of the grid with the new sprinklers fed from a line then that would most likely present a problem. Feeding those same two heads from a new pipe fed from the end of the main wouldn't be as long as the new pipe was equal in size to the branch line grid piping.

The worst situation, perhaps even worse then coming off the grid, would be to run 100' of 1" pipe from the end of the main. It would be like having a 20' high building with a 10'x10' by 50' tall silo requiring one sprinkler adjacent to the riser. More then likely this would be your hydraulically most remote area.

Those that have experience can generally look and tell where there might be a problem right away. You've done it enough times you know especially if you're old enough to have done calculations by hand. You certainly know what an unbalanced system does.

 

[TravisMack]

As far as pipe scheduled systems go, I have been told to be careful on those because if you add a head to a branch line, you are possibly exceeding the pipe schedule.

For example, if you have 5 heads on one side of a cross main and you add a 6th, your starter piece needs to be 2" per the pipe schedule. So, at that point, I have had AHJs require calcs. You may not be able to go back to the closest main because of the schedule as well.

If it is a calculated system, unless I am working in the hydraulically remote area, I am not too concerned about calcs for adding / relocating sprinklers. We rarely take more than 1 sprinkler per 1" outlet off of the original branchline.

So, depends is a good answer. It depends on your situation at hand.

Travis Mack
MFP Design, LLC

 

[Jeremiah187]

Depends is a great answer.

Unfortunately our buddies at the Gov. do not like depends as an answer. hahah

I was hoping to get some code section or phrase so I can prove to them a calc. is not required.

But looks like it just may take some detailed explaining.

But thanx for the responses. We all need to push NFPA to add in more instructions on this subject.

 

[stookeyfpe]

Jeremiah

We do not need to be pushing NFPA for instruction. This question comes down to the selected sprinklers and the scope of work.

The 20 sprinkler rule that CDA mentioned originally come from Texas State Board of Insurance before it became the Texas Department of Insurance. That rule was used when the world revolved around the use K=5.6 or K=8.0 sprinklers. Those days are over.

With all the available sprinkler technology available, I find that simple TI's need calculations, especially when dealing with extended coverage sprinklers or sprinklers used in storage occupancies.

Depends is a broad, widely interpreted word for good reason.