NFPA 101 (1-hr) or NFPA 90A (2-hr) in 4-Story Shaft?

1/21/2025

NFPA references are based on current editions. While NFPA 101, Section 30.3.1.1.4 (New Apartments) allows vertical penetrations to be protected with a 1-hour rating when sprinklered, NFPA 101, Section 30.5.2 requires HVAC equipment to comply with NFPA 90A.

According to NFPA 90A, Sections 9.1.3 and 6.8.3, a higher level of protection is required for shafts that penetrate more than four floors (2-hr fire rated and fire dampers).

Does the exception provided in NFPA 101 permit reducing the required fire rating to 1-hour for duct shafts, or does NFPA 90A take precedence?

I'm curious to hear different perspectives on this.

I can understand both sides of the issue but find it challenging to justify allowing a 1-hour fire rating for a vertical exit within a New Apartment while requiring a 2-hour fire rating for the duct shafts.

Thanks in advance.

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11 Comments

Christopher Nelson

1/21/2025 08:22:05 am

I would say this is similar to other situation where this accounting for building construction rather than stories. NFPA 101 7.1.3.2.1 requires exits 4 or more stories to be 2 hrs unless and existing building which you are not.

Im thinking this more for a Type IA/IB/IIA 3 story structure rather than 4 or more stories apartment.

Go with the normal 2 hr when connecting 4 or more stories.

Ricardo Gonzales Jr

1/21/2025 08:45:50 am

If both NFPA documents are adopted by the jurisdiction, most AHJs would use the more stringent of the two. Note the 1st word of the sentence above. It also depends on the AHJ on which department owns the building and its ratings vs. a single department responsible for it all. If it's compartmentalized, it could be the responsibility of the Mechanical, Architect or Fire Life Safety.

Pete D

1/21/2025 09:18:48 am

I'd like to echo this with caution. NFPA 101 is not adopted by all jurisdictions, and it differs from IBC. I also want to comment, if your structure is IA, as classified by Table 601 IBC and the jurisdiction is on IBC, you have a 2 hr slab rating. The vertical duct can be "shafted", which I guess is jargon/vernacular for wrapped in fire rated material to carry the rating for the slab up to the next slab. That could mean 2 layers of 5/8 type X gypsum on a minimum 3 5/8 stud wall with base of wall and head of wall fire stopping, or a 2-hr shaft wall around the duct. Typically, we're cladding the duct for aesthetics anyway. I caution that the devil is in the details. You need to ensure for a conventional wall you're using UL, cUL, or Intertek or some listing agency recognized by your jurisdiction. My last comment is, in IA construction the slab penetration must have a T, F, and L rating. Understand the difference. It must block fire, temperature increase, and the leakage of air/smoke. Fire dampers come in 1.5 hr and 3 hr, and you will use the 90 minute fire/smoke damper for the 2 hr rating. They make butterfly dampers that are inside the duct beneath the slab penetrations that operate on mechanical links and torsion springs. These are ideal if it's a bulk run of duct without any branch offs. Otherwise, if the duct is wrapped in fire-rated material, any tributaries that branch off on the intervening floors will need fire-smoke dampers, which require mechanical actuation of the fire component and electronic actuation of the smoke component with a duct detector installed within 5 feet of the damper.

Todd E Wyatt

1/21/2025 09:08:17 am

If (only) NFPA 101 Life Safety Code - 2024 (LSC) is the adopted, scoping Code for this Project, LSC takes precedence over Referenced Publications per Chapter 2 :

LSC
Chapter 2 Referenced Publications
2.1 General.
The documents referenced in this chapter, or portions of such documents, are referenced within this Code, shall be considered part of the requirements of this Code, and the following shall also apply:
(1)*Documents referenced in this chapter, or portion of such documents, SHALL ONLY BE APPLICABLE TO THE EXTENT CALLED FOR within other chapters of this Code.
(2) Where the requirements of a REFERENCED CODE OR STANDARD DIFFER from the requirements of this Code, the requirements of this Code shall GOVERN.

2.2* NFPA Publications.
NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, 2024 Edition.

NFPA 90A is referenced (32) times in LSC but NOT in the sections prescribing the fire-resistance rating (FRR) for shafts :

LSC
Chapter 8 Features of Fire Protection
8.6 Vertical Openings.
8.6.4 Shafts.
Shafts that do not extend from the bottom to the top of the building or structure shall comply with 8.6.4.1, 8.6.4.2, or 8.6.4.3, as modified by 8.6.4.4 or 8.6.4.5.
8.6.5* Required Fire Resistance Rating.
The minimum fire resistance rating for the enclosure of floor openings shall be not less than as follows:
(1) Enclosures connecting four or more stories in new construction shall be 2-HOUR FIRE BARRIERS.
A.8.6.5
The application of the 2-hour rule in buildings not divided into stories is permitted to be based on the number of levels of platforms or walkways served by the stairs.

NFPA 90A is only referenced in Chapter 8 Features of Fire Protection per the following :

8.5.5.4 Installation, Testing, and Maintenance.
8.5.5.4.1
Air-conditioning, heating, ventilating ductwork, and related equipment, including smoke dampers and combination fire and smoke dampers, shall be installed in accordance with NFPA 90A, NFPA 90B, NFPA 105, or NFPA 80, as applicable.

Jordan

9/17/2025 08:47:09 pm

Received some additional clarification from NFPA on this. Todd E Wyatt hit the nail on the head.

Yes, the HVAC shaft can have a 1- hour rating. NFPA 101, Section 2.1(2) states that NFPA 101 will take precedence over other standards that have differing requirements. Therefore, HVAC shafts can comply with the requirements of 30.3.1.1.4.

Jeff Ayers link

1/21/2025 09:41:26 am

The NFPA design standards appear to be driven by IBC building classifications. For wood Apartments its primarily Type VA & VB (4 stories or less) & Type IIIA and IIIB 5 stories of wood.

You wrote: "shafts that penetrate more than four floors (2-hr fire rated and fire dampers)" more than 4 floors places you in a Type IIIA with the exterior load bearing wall 2 hours, vertical shafts are 2 hours, steel protection is 2 hours etc., floors are 1 hour.

While Type IIIB allows combustible material on the floors and roofs (FRT not required) the floors still have 1 hour rating for penetrations similar to VA & VB.

Floor to floor penetrations (vertical openings) are typically 1 hour even though mechanical duct shafts are 2 hours.

Your question appears to be confusing 3 different terms:
Vertical openings are penetrations in the rated floor.
Shafts are rated enclosed openings around holes in the floor.
Vertical exits are stairwells with 2-hour walls (typically). Type IIIA has 3-hour walls separating the floor areas and usually has a shared wall at the stair / demising wall.

Maybe you can clarify your question, because the codes you reference do not seem to get to the heart of your question.

Jose R Figueroa

1/21/2025 11:57:43 am

The difference comes down to how NFPA 101 and NFPA 90A approach safety. NFPA 101 offers a bit more flexibility—if you install sprinklers, you might be able to reduce ratings a bit. On the other hand, NFPA 90A takes a stricter stance when it comes to HVAC shafts because they can quickly spread fire and smoke between floors. It's all about finding the right balance for fire & life safety. Consult your AHJ.

1/21/2025 12:42:58 pm

I must include NFPA92 in the discussion. The HVAC system should also be a smoke control system. The HVAC system should be built according to NFPA 90 and 92. It will meet NFPA 101 requirements automatically.

Wes

1/21/2025 12:48:38 pm

An HVAC system for a four story building does not automatically become a smoke control system under NFPA 92. A smoke control system is far more involved than an HVAC system.

Jack G

1/21/2025 12:27:09 pm

Assuming it is not HT construction or roof is not 20 ft higher than the floors.
VA— construction does not allow 13r or 13 d systems.
VB — does not allow 13 r or 13d over 2 stories.
Also to reiterate LSC codes are not a part of NFPA 13. The NFPA 13 appendix addresses that 101 is not a part of the 13 standard.
Also there are certain size closets that 101 permits you not to protect with sprinklers. This is not permitted.
Any area increases or fire rating reductions are also not permitted by the IBC.
Review the IBC commentary section sheet that charts what type system is permitted, 13, 13r, or 13 d.
There are also superscript notes that indicate ( as long as protection is extended into the area ( open wood joist s between floors, attics, balconies etc)
As HVAC floor penetrations allow exposure to all floors, thru the shaft, the rating reductions of the shafts and floors would not be allowed. ( personally, I would protect the top too, below the roof line— dry sidewall if unheated)
So it basically depends on how the building is constructed.

Mike

11/19/2025 08:54:07 am

I’m working in a multi family apartment and it has a 10 x 10 dryer duct 2 hour fire rated shaft. My blue print show a 4” 90 with 22” pipe up inside the shaft. Will this cause lint buildup and a fire. Is this Method recommended.

NFPA 101 (1-hr) or NFPA 90A (2-hr) in 4-Story Shaft?

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