Running pipe under raised floor

[bdk]

I have a project where the architect would like us to run the sprinkler pipe under a raised floor to feed the area below (sleeves or core drilling to install pendent heads). This area will also be used for the HVAC supply to the same area.

Is there a place in NFPA or IBC/IFC that requires the support of piping to be UL listed, if it is located on the floor, or could a two hole strap or unistrut be used to secure the piping in place?

 

[stookeyfpe]

Hangers for sprinkler piping must be listed for fire protection service unless the design is engineered.

 

[TravisMack]

We frequently use unistrut for something like this. Technically, you aren't hanging the piping. The floor is supporting the piping. All you are doing is securing it in place for ease of installation. I believe you would still need to provide the appropriate seismic bracing if required.

 

[stookeyfpe]

As much as I respect and appreciate Travis's logic the 2002 edition of NFPA 13, section 9.1.1.4 specifies a listed assembly. Section 9.1.1.1 explicitily states that the chapter addresses the support of piping from a structure, and this was the original question.

The method of supporting the piping must be listed.

Sorry for the slow response but I have been traveling on business.

 

[SprinklerDesigner2]

Stookey is right as usual.

Unistrut is often used to support pipe feeding hose drops and supporting drops to the inspector's test connection.

This isn't listed but we all got engineer friends who can seal so get a buddy to seal a detail drawing on an 8 1/2 x 11 paper that you can xerox off.

 

[stookeyfpe]

SD2:

Don't be copying the original design and using it on other projects. In the State of Texas your described action is a violation of the Texas Engineering Practices Act and more important, each design in which a seal is affixed is based on specific conditions.

This is why I responded to Travis's question. Unistrut is a form of an adult erector set. Unistrut, like all other materials, has its own limitations.

Pay the fee, have the pipe support design prepared by a PE, install it in accordance with the engineer's design, NFPA 13, and make the AHJ happy. Anything else exposes the engineer to liability that will be directly shifted to you because you applied a design for one job onto another. It is not worth it.

What scares me about the original post is that we do not know where BDK's design is located. If he is on the West Coast, and his building is located in a high Seismic Design Category, the Unistrut category may not work for the design seismic conditions. This is what I hate about these pre-engineered building utility support systems like Unistrut. It can be so easily misused and the engineer pays with increased Errors and Omissions Insurance fees.

 

[TravisMack]

This is based on an AFSA interpret I remember from long ago. My memory of it may not be correct any longer. But, here goes:

If you are running the piping on the floor, it is being supported by the floor. The unistrut is only a "convenience" to keep the piping in place. The unistrut is doing nothing to support the piping. Therefore, it is not required to be listed.

If you install piping through open web joists, and lay it on the bottom chord of the joists, it is being supported by the bottom chord. You could in theory, use "zip ties" to hold the piping in place for convenience, as it is not a hanger. The piping is being supported by laying on the joist.

When you hang the piping, that is when you need the listed componets; such as swivel ring, AT rod and beam clamps.

Now, I have never been so brave as to try to get by with "zip ties" as that just seems strange, but I have heard rumors of contractors doing it. If you are in a building that is requiring seismic protection, then regardless of the hanger method, you still must provide the appropriate seismic bracing / restraing.

I can understand the rationale for piping on the floor being secured for convenience. After all, what is a hanger for? It is to support the piping in the air. If the piping is laid directly on the floor, then no additional support is required. You are only using the unistrut as convenience to keep it in place during the installation.

Now, supporting the piping down a column to hose drops is a different story, but can be accomplished if sealed by a Structural PE.

What say ye?

 

[stookeyfpe]

Call me old fashioned or call me a purist, but I still believe Chapter 9 applies and the hanger must be listed. The floor in the original post is a structural element designed for the support of people and equipment. The pipe hangs from underneath the floor.

The original post states that this in a plenum so an air space exists between the pipe and the supporting elements. Therefore the hanger or Unistrut or whatever system is used must be listed or the design must be sealed by a registered professional engineer.

I do not have an issue with using Unistrut in this application. In fact, I encourage it because it is an inexpensive and reliable solution. But to use it, one must comply with NFPA 13 Chapter 9 and accordingly, have the design sealed by a registered professional engineer - or use a listed hanger.

 

[TravisMack]

Stookey:

I thought he was saying the piping was laying on the concrete floor below the raised floor, not being supported from the raised floor. If it is being hung from the raised floor, then yes, all components must be listed.

What we typically do in these situations for protection of piping under a raised floor is to lay the piping on the concrete floor, then sprig up to the heads as needed. Typically, these spaces are 18-24".

So, if it is being "hung" then yes - I agree - all components must be listed. If it is being strapped to the concrete floor, then I think the unistrut anchored to the floor is perfectly fine.

 

[stookeyfpe]

Travis

The way I read the original post one could go either way. And I now understand your application and agree with your use of Unistrut. If it is laying on a structural surface, then it would not be required to be listed.

In my own humble opinion I think the NFPA 13 committee should look at this issue but I will let it go at that.

 

[bdk]

Travis & Stookey,

For clarification, the project is in MN so no need to worry about seismic bracing, and my intent was to secure the pipe to the floor with unistrut.

Thanks for the input it’s always helpful.

 

[TravisMack]

Stookey:

Again, I agree. The use of items in this should be clarified by the 13 committee for hanging and bracing. Maybe, one day, I will get on one of these committees and have fun with people

T

 

[stookeyfpe]

Travis

The problem is that the committees are populated with special interests and the folks who are needed to develop the solutions are excluded.

The sad thing is that Unistrut is probably not even aware that its materials are used in NFPA 13 systems or, even if they are, it is such a small marketshare that the cost of listing the material is not worth it to them.