# Underground Sprinkler Piping



## duckbill (Dec 1, 2012)

Since the Builder's Association of PA has effectivly block the adoption of any new codes beyond 2009, my question is from the 2007 NFPA 13 as referenced by the 2009 ICC Codes.  I am reviewing a structure with four buildings and three open breezeways under one roof.  This is an apartment building with open stairs to the second floor units located in the breezeways.  There is a 4" DIP supplying the sprinkler system from the authority main to a mechanical room in the basement of one of the center apartments.  From the mechanical room, the sprinkler contractor wants to run piping underslab to feed the remainder of the units.

2007, NFPA 13, Section 10.6.1 forbids pipe to be run under buildings.  Section 10.6.2 permits this installation if the pipe is in covered trenches and valved to isolate the pipe.  Has anyone encountered sprinkler piping run under the slab?  Does this section only refer to fire service mains or any sprinkler piping?


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## cda (Dec 1, 2012)

Not a good idea and have not allowed it except for about five feet into the building

Also look at Nfpa 20 says about the same thing

If this is new const would be easier and better to run outside the foot print

How many sq ft is each if these buildings??

And us it showing a riser per building??

And clarifying one roof with four buildings under it??


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## cda (Dec 1, 2012)

And the answer is??

How many sq ft is each if these buildings??

And us it showing a riser per building??

And clarifying one roof with four buildings under it??

Also 13 or 13???

Attic sprinkled???


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## duckbill (Dec 1, 2012)

Thank you for the response cda.

Yes, four buildings under one long continuous roof (250').  The four buildings are separated by an 8' space (breezeway).  This space serves as a weather protected entry for the stairs to the second floor apartments.  The breezeways are open to the elements at the front and back of the building.  The total under-roof area is about 16,000 sf.

It seems the contractor could install the main into the mechanical room with backflow, FD connection, etc., then branch back outside to the other buildings.  Does that make sense?

Needs NFPA 13 for the building area.

Risers shown in each individual building only as a connection point to the system in each buiklding.


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## duckbill (Dec 1, 2012)

Attic is sprinklered - dry system.


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## cda (Dec 1, 2012)

With out seeing a site plan hard to give a good answer

Seems like each building is not that big

Looks like could possibly run it through the attic, but only problem there is freezing

I take the breezeways are sprinkled??

Possibly run the supply through those

Is four inch going to do it?? With doing the attic

I am still thinking since they are planning underground already, just do it correctly


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## duckbill (Dec 1, 2012)

Thanks cda.

The breezeways are sprinklered.

Four inch main into one of the four buildings...the only building with a basement housing the mechanical room.

From the mechanical room, contractor shows two inch branches into each of the four buildings under the slab in the center of the structure.


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## cda (Dec 1, 2012)

Does not sound good

Once again without seeing a plan, hard to make a good call

But I do not think I would approve it


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## Builder Bob (Dec 4, 2012)

Would not recommend running piping under slab........ blow out issues if used.


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## FM William Burns (Dec 4, 2012)

Like others have mentioned, I would also *not recommend* it based on the following NFPA 13, 2010 (similar in 07)………. If this is a planned project the installer would be better advised to run a service along the utility side of the structure with individual taps/service to each building. The owner should also be advised because the potentials for damages with settling and interruption are real and much more expensive then planning for additional riser rooms/closets. Just saying……..

_10.6.1 Pipe shall not be run under buildings. [24:10.6.1]_

_*Handbook:*__ When buildings are built over existing underground piping, the piping should be rerouted around the new building for several reasons. Piping located under buildings is extremely difficult to repair, which is one of the reasons that 10.6.1 prohibits the installation of pipe under buildings. When piping under buildings requires repair, operations in the building must be curtailed, equipment may need to be moved, and the floor must be excavated. Leaks in the buried piping underneath the building can go undetected for long periods, and they can also undermine the building support. The location of system valves in the center of a building also places the system controls in the center of the building, which may not be desirable during a fire event._

_10.6.2 Where pipe must be run under buildings, special precautions shall be taken, including the following: _

_(1)_ _Arching the foundation walls over the pipe_

_(2)_ _Running pipe in covered trenches_

_(3)_ _Providing valves to isolate sections of pipe under buildings_

_[24:10.6.2]_

_*Handbook:*__ Subsection 10.6.2 outlines some of the measures that can be taken to minimize exposure to damage but that do not completely eliminate it. Where the main penetrates the foundation wall, arching of the foundation wall over the main or other means of ensuring system and structural integrity needs to be provided._


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## RJJ (Dec 4, 2012)

I agree with cda,BB and FM! This is not a good long range issue and should be avoided. The section FM cited are spot on.

Many contractors feel that the piping can be extended under ground just like plumbing drains. Not so for reasons stated.

Entering the building for a few feet to the sprinkler room the piping would need a relieving arch and thrust blocks for the 90 up sweep.


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## sdpaddler50 (Dec 4, 2012)

As others have noted fire mains under the slab is not a good thing. Have you ever seen the result of a blowout. I bet you could find some pics if you googled it. I have seen it in person sevaral times. The last one involved 175 psi pump pressure at the elbow feeding the riser and it was ugly. If that main had extended completely under the building it would probably have been red tagged.


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## RJJ (Dec 5, 2012)

Problem is with one story pad sites,like restaurants etc that have no basement in frost areas you have to come under the slab. The location of the sprinkler room needs to be located as close as possible to the penatration of the foundation and rise to the room.

I m ok with this! But would not allow extended service beyond the closest point. I would not agree with the original post condition.


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