Hanging Directly from Metal Deck under NFPA 13?

10/9/2019

NFPA 13 (2016 Edition) Section 9.2.1.4.1 states:

9.2.1.4.1 Branch line hangers attached to metal deck shall be permitted only for the support of pipe 1 inch of smaller in size, by drilling or punching the vertical portion of the metal deck and using through bolts.

The Sammy X-Press has listed hangers that call out attachment directly to metal deck for pipe up through 4" in some cases.

From a code perspective, does the section above not apply, or would this be a code approved alternative? Just looking for the code logic that would allow use of listed special materials where the section above wouldn't trump this method.

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7 Comments

Wayne Ammons

10/9/2019 08:39:22 am

Products specifically LISTED for use on fire sprinkler systems are allowed by NFPA 13. Below is commentary from the 2016 edition of the NFPA 13 Handbook on this particular subject:

9.2.1.4 Metal Deck
The NFPA allowance for attachment to decking material applies only to very small diameter pipe using through-bolts. With the exception of 9.2.1.4 and that for toggle hangers in 9.2.1.1.2, hanger attachment must be made to the building structure.
Hanger manufacturers have created specialty products with listings to attach to steel deck of varying gauge. It is acceptable to use these listed products, but consideration must be given to more than just the steel to which the fastener is attached. While locally the fastener might be in compliance with the minimum deck gauge requirements of the hanger manufacturer, the deck itself must still meet the requirements of 9.2.1.3.1. For example, a ceiling flange with a specific listing is to be screwed to steel metal deck as thin as 22 gauge. While connection of the ceiling flange to the 22 gauge deck might be fine, the steel deck’s span must also be checked to see if it meets the requirements of 9.2.1.3.1 for the building. It is one thing to determine that the ceiling flange not to pull out the deck, but it is another thing to see if the deck will support the water-filled pipe plus 250 lb (115 kg) as it spans between supports.

Keep in mind, commentary from the handbook is not part of the standard itself. You might also refer to the equivalency statement at the beginning of NFPA 13 to support the use of listed products not directly covered by the standard:

1.5 Equivalency
Nothing in this standard is intended to prevent the use of systems, methods, or devices of equivalent or superior quality, strength, fire resistance, effectiveness, durability, and safety over those prescribed by this standard.

Skyler

10/9/2019 12:03:38 pm

The commentary hits it on the head. It all depends on the thickness of the deck, but NFPA 13 basically says that for 1" it doesn't matter. Composite metal decks typically range from 16 to 22 gauge, with 18 and 20 being the most typical. Metal roofs on a pre-engineered purlin structure tend to be 22 or 24 gauge. Purlin thicknesses can range wildly, but they are one of the best use cases for the Sammys you referred to.

The Sammy you referred to is FM Approved for up to 2" in 22 gauge or thicker (very common), but up to 4" requires at least 12 gauge (not very common in the wild). In any case, it is important to pay attention to that listing information on the Sammy.

It's all about the metal thickness you are attaching to.

J. Wilson

10/9/2019 10:26:49 am

The point is that if it listed by manufacturer it is acceptable. Follow all manufacturer instruction your good.

Skyler

10/9/2019 12:11:21 pm

Just noticed the actual question you posed. I would refer you to the section in the beginning of the hanging chapter (9.1.1.2) that allows an Engineer to use alternative hanging methods and lists the criteria. This is very useful for non typical situations. Since you are an Engineer, I would say you can use this section to justify the use of the Sammys you referred to (just pay close attention to the metal thickness you are attaching to).

Wayne Ammons

10/9/2019 01:57:01 pm

Skyler,

Wouldn't section 9.1.1.2 (below for others reference) refer to a hanging method or device that is not already listed or approved by a nationally recognized testing agency, i.e. UL or FM? For example, a fabricated bracket to support pipe along a wall.

9.1.1.2
Hangers certified by a registered professional engineer to include all of the following shall be an acceptable alternative to the requirements of Section 9.1:
(1) Hangers shall be designed to support five times the weight of the water-filled pipe plus 250 lb (115 kg) at each point of piping support.
(2) These points of support shall be adequate to support the system.
(3) The spacing between hangers shall not exceed the value given for the type of pipe as indicated in Table 9.2.2.1(a) or Table 9.2.2.1(b).
(4) Hanger components shall be ferrous.
(5) Detailed calculations shall be submitted, when required by the reviewing authority, showing stresses developed in hangers, piping, and fittings, and safety factors allowed.

On the Clock

10/9/2019 03:34:28 pm

I agree 100% with Wayne's comments above. Note that the building structure also must be capable of supporting the load as described in NFPA #13 (2016) 9.2.1.3.1. When they first came out (and before I knew better), I was guilty of overly-liberal use of Sammy XP's. I offer this as a caution, on my projects, the structural engineer-of-record routinely prohibits, or greatly limits hanging directly to the metal deck, regardless of the gauge of the deck. And it can vary project-to-project.

Wayne Ammons

10/9/2019 04:16:39 pm

Excellent point. Whenever we (my company) wish to hang directly to the metal decking, we always get approval from the structural engineer or GC, regardless of what we know about the steel gauge.

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