MeyerFire
  • Blog
  • Forum
  • TOOLKIT
    • ALL TOOLS
    • BUY THE TOOLKIT
  • UNIVERSITY
    • ALL COURSES
    • JOIN THE UNIVERSITY
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE PREP SERIES
    • PE 100-Day Marathon
  • LOGIN
    • TOOLKIT-ONLY LOGIN
    • UNIVERSITY LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • OUR CAUSE
    • ABOUT MEYERFIRE
    • JOB OPENINGS
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT
Picture

Calculate 3,000 sqft for TJI w/ Attached Gypsum?

9/28/2021

10 Comments

 
We have a hotel that is constructed with 12-inch TJI joists (composite engineered wood joists which have a continuous web, not an open web). There are gypsum ceilings attached directly to the bottom of the TJI joists. There is also at least 3.5-inches of insulation above the gypsum ceilings.
Picture
Are we required to calculate 3,000 sqft or 8 residential sprinklers, or do we meet the noted code exception below?

NFPA 13-2019 19.3.3.1.5.2(4) Item (10): Light or ordinary hazard occupancies where noncombustible or limited-combustible ceilings are attached to the bottom of composite wood joists either directly... , provided the adjacent joist channels are firestopped into volumes not exceeding 160 cubic ft, using materials equivalent to 1/2-inch gypsum board, and at least 3-1/2 inches of batt insulation is installed at the bottom of the joist channels when the ceiling is attached utilizing metal channels.
Picture
What are the "adjacent joist channels"?

And does the construction we have equal the firestopping as noted?

Does the gypsum ceiling attached to the bottom equal the firestopping, or is the firestopping something additional?

Roland Huggins wrote a good article on this issue, but I'm still not sure.
https://sprinklerage.com/sprinkler-protection-3000-ft2-modifier/

I have another senior tech convinced that this section is referring to an "unprotected" or non-firestopped combustible concealed space.

Thanks in advance.

​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
10 Comments
Mike
9/28/2021 08:13:40 am

Fire stopping is blocking perpendicular to the joists. This is the fire stopping to limit the volume.

Each joist bay needs this.

What did the estimator who sold the job anticipate?

Reply
Alex
9/28/2021 09:48:25 am

Hi Anonymous,

Awesome post! Shout out to Meyer fire for providing some great details to go along side the question as well. This is an ongoing discussion and I believe Roland did a good job within his article. With that said, I tried my best to explain my thought process.

To answer your first question, I do not believe that you require a minimum area of sprinkler operation of 3000 Square Feet. Based on NFPA 13 (2013) 11.2.3.1.4 4(j) (Same code section you listed within the question from 2019), as long as the adjacent joist channels are fire stopped into volumes not exceeding 160 Cubic Feet, you do not need to increase your design area. This leads into your second question:

Its my understanding of the code that a joist channel is what is shown in the second diagram/picture. The adjacent joist channel would be the joist channel to the left and right of the diagram. From the code, if your channels are greater than 160 cubic feet, you need to use materials equivalent of ½ in. gypsum board to block off each channel. (Example: if your joists are 16 inches on center and 12 inches deep, every foot would be slightly under 1.33 Cubic Feet. Meaning, every 120 feet, you would need to provide firestopping.

The construction you have shown matches the code as I interpret it. As far as firestopping goes, I believe the 3.5 inches of insulation is only required when you are utilizing metal channels to hang the ceiling. If you are attaching the gypsum directly to the joists, batt insulation is not required as long as the gypsum provides the same fire resistance as the insulation would.

The above is simply my understanding and interpretation of the code. I look forward to what others have to say!

Best of luck with your design,
Alex

Reply
Anonymoose
9/28/2021 01:41:07 pm

Reading that article it seems that you would need to put gypsum parallel to the joists to divide the spaces into 160 CF or less.

Question for y'all, If that's the case, would you be able to exclude the 3.5 inches in calculating the space, meaning for 12" joists you'd get about 160 SF / (8.5/12) ≈ 226 SF in area between firestopped volunes?

Just in case it hadn't been brought up, if your pipe is above the insulation, is anyone signing off on guaranteeing at least 40°F above the ceilings?

Reply
David
9/28/2021 04:48:49 pm

According to an NFSA interpretation (May 2007 #6) the volume must be calculated without taking the insulation into account. The NFSA expert of the day references intent sourced from previous editions of NFPA 13.

Side Note: I have found the Expert of the Day 2004-2018 volumes to be very helpful when interpreting NFPA 13. Thanks MeyerFire for working with NFSA on getting those published.

Reply
Anonymoose
9/28/2021 05:32:52 pm

Good to know, thanks!

David Kulbacki
9/29/2021 09:08:03 am

Looks like the 2019 edition cleared this up, and you can discount the volume taken up by the insulation. My mistake.

David Kulbacki
9/28/2021 04:52:11 pm

One thing to watch out for are the manner by which the joists are hung. I have seen quite a few joist hangers used that don't allow the joist to but hard up against the beams they are hung from. The result is that there is a gap where the joist meets the beam that will allow fire spread from joist channel to joist channel.

Reply
Mr. Quixote
9/29/2021 02:01:54 am

There is lots of confusion regarding this topic, but lets start at are sprinklers required within the TJI (Composite wood joists), assuming 13 code application of course.

Generally no, and according to 13 2019 9.2.16, as long as the JOIST CHANNELS as measured from top of insulation (note this, as it's come up in previous replies) are separated into volumes not exceeding 160 cubic ft using materials equivalent to web construction, then the areas within the joists shall not require protection. I think this is obvious, but JOIST CHANNEL is the space between each individual joist as shown in the image.

So what are "materials equivalent to web construction"? Well, TJI webs are generally just a type of OSB or thin wood substrate, and NFPA seems to imply that insulation may meet this requirement. In reality, the intent here is not "firestopping", as I typically see, but more like draft stopping. It's simply there to keep a draft from spreading throughout the structure and spreading a fire. You could typically see 2x wood, but plywood, osb, drywall, insulation seem to all be acceptable as "equivalent to web construction". .

For a 16" deep x 16" on center TJI, it would take 90' approximately to exceed the 160 cubic ft. require to sprinkler between joists. And, if that situation occurred, it may be as simply as adding a 2x block of wood to separate that area within the JOIST CHANNEL. And note that this does not include insulation depth, which can be subtracted from the area as allowed by 9.2.1.6 2019.

Now to to the more important point, do these areas as described above require an increase in design area size to 3000 sqft or 8 sprinkler heads for the residential special design requirements (residential or room design by 2022) as required by 19.3.3.1.5 2019? The answer is YES generally. However, if you look at 19.3.3.1.5 (B) (below), you will see that if there are no "adjacent areas" to extend the design area too, then the design area would not be required to be extended.

(B) The term adjacent shall apply to any sprinkler system protecting a space above, below, or
next to the qualifying concealed space except where a barrier with a fire resistance rating at
least equivalent to the water supply duration completely separates the concealed space from
the sprinklered area.

In most cases, hotels are highly compartmentalized, meaning that all of the separating walls between all areas are at least a 1 hr rated assembly, and these assemblies extend from the base floor to the floor level above. And the floor assembly is a rated 1 or 2 hour rated assembly.

In conclusion, if you end up with a hotel, light hazard (except a small ordinary hazard mech room), with TJI combustible spaces that require an increase to design area, but in reality, if all of the spaces are divided by at least a 30 min fire rating (2 layers 1/2" gypsum as defined by IBC), then you should NOT have to increase the design area.

It's not a simple question that you ask....are we required to calculate 3,000 sqft or 8 residential sprinklers, or do we meet the noted code exception below?

The answer is generally yes you must increase the area, but given that most hotels are highly compartmentalized with fire rated assemblies, you probably won't have to because all of your fire ratings will qualify as a separation of at least 30 mins.



Reply
David Kulbacki
9/29/2021 09:06:56 am

Looks like 19.3.3.1.5.2 (10) in 2019 edition would allow design area to not be increased.

Reply
RM Ballam
2/10/2022 10:55:51 am

The section requires 1/2" of gyp or equivalent. Most volumes created by composite wood joist are much smaller than the 160 cu stated in standard which means that the gyp bd. would only be required every 4th or 5th joist in most situations.
Example: 1x1.33x18=23.94, 160/23.94=6.68
The IBC, Table 722.6.2 (1) state that 1/2" gyp equals 15 minutes, It also states that 3/8" OSB (product used for TJI webs) equals 5 minutes.
Would the 3 or 4 layers of 3/8" OSB meet the equivalent of the 1/2" gyp bd. requirement?
Thanks,
Rob

Reply



Leave a Reply.

    SUBMIT A QUESTION
    Picture
    Why Sponsor?

    ALL-ACCESS

    Picture
    GET ALL OUR TOOLS

    SUBSCRIBE

    Subscribe and learn something new each day:
    I'm Interested In:

    COMMUNITY

    Top April '25 Contributors
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    Picture
    SEE LEADERBOARD

    YOUR POST

    SUBMIT A QUESTION

    PE EXAM

    Get 100 Days of Free Sample Questions right to you!
    SIGN ME UP!

    FILTERS

    All
    A1171
    ABA
    ADA
    ASCE 7
    ASME A17.1
    ASTM E1354
    Blog Thread
    Daily Discussion
    Design-documents
    EN 12845
    Explosion Protection
    Explosion-protection-prevention
    Fire Detection And Alarm Systems
    Fire Dynamics
    Flammable And Combustible Liquids
    Flammable-combustible-liquids
    FM Global
    Human-behavior
    IBC
    ICC 500
    IEBC
    IFC
    IMC
    IPC
    IRC
    ISO
    Means Of Egress
    NBC
    NFPA 1
    NFPA 10
    NFPA 101
    NFPA 11
    NFPA 110
    NFPA 1142
    NFPA 1221
    NFPA 13
    NFPA 13D
    NFPA 13R
    NFPA 14
    NFPA 15
    NFPA 16
    NFPA 17A
    NFPA 20
    NFPA 2001
    NFPA 214
    NFPA 22
    NFPA 220
    NFPA 24
    NFPA 241
    NFPA 25
    NFPA 291
    NFPA 30
    NFPA 307
    NFPA 30B
    NFPA 31
    NFPA 33
    NFPA 37
    NFPA 400
    NFPA 409
    NFPA 415
    NFPA 45
    NFPA 495
    NFPA 497
    NFPA 5000
    NFPA 502
    NFPA 54
    NFPA 55
    NFPA 654
    NFPA 68
    NFPA 70
    NFPA 701
    NFPA 72
    NFPA 75
    NFPA 770
    NFPA 82
    NFPA 855
    NFPA 90A
    NFPA 92
    NFPA 96
    NICET
    OBC
    OSHA
    Passive Building Systems
    PE Prep Guide
    PE Prep Series
    PE Sample Problems
    Poll
    Smoke Management
    Special Hazard Systems
    UFC 3-600-01
    UFC 4-021-01
    UFC 4-211-01
    UPC
    Updates
    Water Based Fire Suppression
    Weekly Exams


    ARCHIVES

    May 2025
    April 2025
    March 2025
    February 2025
    January 2025
    December 2024
    November 2024
    October 2024
    September 2024
    August 2024
    July 2024
    June 2024
    May 2024
    April 2024
    March 2024
    February 2024
    January 2024
    December 2023
    November 2023
    October 2023
    September 2023
    August 2023
    July 2023
    June 2023
    May 2023
    April 2023
    March 2023
    February 2023
    January 2023
    December 2022
    November 2022
    October 2022
    September 2022
    August 2022
    July 2022
    June 2022
    May 2022
    April 2022
    March 2022
    February 2022
    January 2022
    December 2021
    November 2021
    October 2021
    September 2021
    August 2021
    July 2021
    June 2021
    May 2021
    April 2021
    March 2021
    February 2021
    January 2021
    December 2020
    November 2020
    October 2020
    September 2020
    August 2020
    July 2020
    June 2020
    May 2020
    April 2020
    March 2020
    February 2020
    January 2020
    December 2019
    November 2019
    October 2019
    September 2019
    August 2019
    July 2019
    June 2019
    May 2019
    April 2019
    March 2019
    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    November 2016
    October 2016
    July 2016
    June 2016


    PE PREP SERIES

    SEE LEADERBOARD

    RSS Feed

Picture
​Home
Our Cause
The Blog
The Forum
PE Exam Prep
The Toolkit

MeyerFire University
​Pricing
Login
​Support
Contact Us
Picture

MeyerFire.com is a startup community built to help fire protection professionals shine.
Our goal is to improve fire protection practices worldwide. We promote the industry by creating helpful tools and resources, and by bringing together industry professionals to share their expertise.

​MeyerFire, LLC is a NICET Recognized Training Provider and International Code Council Preferred Education Provider.

All text, images, and media ​Copyright © 2016-2025 MeyerFire, LLC

We respect your privacy and personal data. See our Privacy Policy and Terms of Service. 
The views, opinions, and information found on this site represent solely the author and do not represent the opinions of any other party, nor does the presented material assume responsibility for its use. Fire protection and life safety systems constitute a critical component for public health and safety and you should consult with a licensed professional for proper design and code adherence.

Discussions are solely for the purpose of peer review and the exchange of ideas. All comments are reviewed. Comments which do not contribute, are not relevant, are spam, or are disrespectful in nature may be removed. Information presented and opinions expressed should not be relied upon as a replacement for consulting services. Some (not all) outbound links on this website, such as Amazon links, are affiliate-based where we receive a small commission for orders placed elsewhere.

  • Blog
  • Forum
  • TOOLKIT
    • ALL TOOLS
    • BUY THE TOOLKIT
  • UNIVERSITY
    • ALL COURSES
    • JOIN THE UNIVERSITY
  • PE Exam
    • PE Forum & Errata
    • PE Store
    • PE Tools
    • PE PREP SERIES
    • PE 100-Day Marathon
  • LOGIN
    • TOOLKIT-ONLY LOGIN
    • UNIVERSITY LOGIN
  • PRICING
    • SOFTWARE & TRAINING
    • STORE
  • OUR CAUSE
    • ABOUT MEYERFIRE
    • JOB OPENINGS
    • BECOME AN INSTRUCTOR
    • HELP/SUPPORT