Hydraulic Calc's Req'd for "Like-for-Like" Repair?

7/6/2022

In a strict "like-for-like" repair, are hydraulic calculations required?

Is there a code basis either way?

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13 Comments

James Phifer

7/6/2022 08:08:53 am

If it's like for like, then nothing has changed and the calculations should be fine. Must be like for like though. Same k-factor or same friction loss characteristics, same equivalent length.

Jesse

7/6/2022 08:12:22 am

That is entirely an AHJ question, and AHJs in my area differ. For most, no. But a few want updated hydraulic calculations to assess how any degradation in the latent water supply may affect design density.

Peter

7/6/2022 08:13:56 am

No. Provided that legacy system didn't use specially listed sprinklers.
Must match pipe schedule.
Must match all sprinkler characteristics. Activation temp, response, orifice.

In some cases, the AHJ may require to recalculate if a permit is pulled, but it's sufficient to show that the water supply hasn't degraded since the legacy installation.

7/6/2022 08:23:29 am

Like for like may be okay in some circumstances, however the code does change. If an old sprinkler system is to be completely redone from the alarm valve or whatever the scope of work happens to be, then everything upstream may require an upgrade. Generally work of this scope will require a permit, and the AHJ will dictate what is to be done. For example, the AHJ may want the system to be updated to current code if the existing system is not up to standards.

I would say any AHJ with knowledge of sprinkler systems would at the very least accept the old hydraulic calculations if given a current flow test that shows the water supply is still adequate.

My code basis for a new flow test being the minimum required is as follows:

NFPA 13 2013 23.1.1* Working plans shall be submitted for approval to the authority having jurisdiction before any equipment is installed or remodeled.

I would still consider this install a "remodel"

I would start by resubmitting the existing plan with a new flow test showing the old hydraulic demand is under the new water supply curve.

23.2.1.1* Where a waterflow test is used for the purposes of system design, the test shall be conducted no more than 12 months prior to working plan submittal unless otherwise approved by the authority having jurisdiction.

Hopefully your AHJ will accept this.

Dan Wilder

7/6/2022 08:32:26 am

13 19' Edition for Existing System Modifications

Nothing specifically (to my knowledge) says "Like for Like" doesn't trigger additional requirements, it just deals with "When" system modifications occur, this is what to do.

I would argue that is the required signage is on the riser, the water supply has not changed, and everything is going back in the same (just newer) that calculations would not be required.

Most of my jurisdictions follow this approach via modifications or agreements after the fact.

Glenn Berger

7/6/2022 08:34:18 am

The above is a very good discussion on this subject. Just curious, why is there going to be a "like for like" repair being preformed?

Adam Jensen

7/6/2022 10:34:37 am

I posed the question.

This is a large (multiple acre) manufacturing facility with a detached pump house. A 16' long section of 12" steel flanged pipe sprung a leak, and further investigation showed pocking throughout this section. The damage is pretty well isolated to this one section of pipe. The cause is unknown. Other repairs include several instances of ongoing leaks and excessive corrosion at threaded joints. All the work is in the pump room. Previous plans for the plant are not to be found.

Glenn Berger

7/7/2022 08:14:36 am

Recommend getting a water analysis preformed. What is the source of the water supplied to the site?

AB link

7/6/2022 08:37:36 am

You as the designer will have to decide if you are comfortable with the changes you are making - comfortable that they are not affecting the original design; pipe is the same, elevations are the same, drops are the same (flex versus hard-pipe), sprinkler heads are still flowing the same GPM as originally calculated, fittings, etc.

Is there an occupancy change? Are the changes being made in an area close to the system riser? Are you making changes to the hydraulically most demanding area? Did they remove/add walls that may affect your sprinkler spacing/demand?

In the end, it all comes down to what the AHJ wants.

We do work in Raleigh, NC and are required to provide hydraulic calculations for ALL renovations, including a one-head add. We do not have to provide a full analysis - however, we have to provide calculations back to a point on the existing system (if we have the existing system calculations showing the original demand). We design and submit system modifications referencing NFPA 13, 2016, 8.15.20.5 Revamping of Hydraulic Design Systems while also referencing the Annex note: "It is not the intent of this section to require a full hydraulic analysis of the existing piping system in addition to new sprinkler layout". (It's probably good to note that the Annex note has been removed from newer editions of NFPA).

Now... I don't necessarily agree with providing a one-head calc for a light hazard room adjacent to the riser room... however silly I think it is - I'm held to it by the AHJ's requirements for plan submittal.

Honestly... it took me longer to write this comment than it would to provide a calculation. If you're using a computer based program, it's typically a quick process. Maybe that's the answer and you'll be able to sleep at night knowing you did the "right" thing. I don't know...

Ultimately, if the AHJ doesn't have a standard regarding when to provide calculations, it's a judgement call.

Anthony

7/6/2022 08:47:02 am

In a like for like replacement 'most' code treats it as a repair and leaves it alone.

Remember if you're replacing hard pipe with flex drops that's not 'like for like' and many over seeing bodies will ask for a clac then.

sean

7/8/2022 09:13:53 pm

One question would be from the AHJ what proof does the existing system is in compliance. Could the original be pipe schedule? Were modifications made from the original design?

AHJ

7/9/2022 06:22:20 am

As an AHJ and FPE (Go Terps!), I require a scope of work letter that states the nature of the repair/replacement. In most cases, a like for like will not trigger a plans review. I also have field inspectors that usually visit the work site to view the progress and scope of work. If in his judgement, the work goes beyond the original scope, then a work stop order is issued and a formal plans review will be required in order to continue.

Work of that nature is usually done by local fire protection contractors, all if whom are known by our office, so we usually don't have any problems.

In my opinion, it really is a judgement call as to when to require formal plans for repair/replacement and like for like work.

Alex

7/9/2022 09:50:45 pm

Hi,

Responding a few days late here - spent the time away with family for the 4th.

This is too funny. I just responded on the flex head requiring calculations (before reading this question) and said if it was a like to like, I wouldn't require calcs.

I wouldn't require for a 1 for 1 if it is truly similar.

Thanks,
Alex

Hydraulic Calc's Req'd for "Like-for-Like" Repair?

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