# Fire Alarms on Wood TJI Ceiling (Exposed)



## eyan50495 (Jun 21, 2020)

Hi All

I am trying to determine the fire alarm requirement for a composite wood joist (TJI / Glulam) ceiling. Ceiling height is 12' floor to floor with 24" TJIs.

Although I have an answer from the local fire alarm contractor and know that our county fire marshal points to NFPA 72, I still want to see where this requirement is in the code or if it is something the fire marshal is adding.

This is a commercial building 1 story + basement, mercantile use. Looking at NFPA 72 (2019), 17.7.3.2.4 lists the requirements for 'SOLID JOISTS'. Then it calculates the spacing of fire alarm detectors based on a percentage of depth of the structure to the ceiling height. 

I don't see anything about composite joists/beams like TJIs and I am well aware they combust differently than solid or dimensional lumber. Is there a definition of solid joist or a requirement for composite joists I am missing? Similarly what would the requirement be if it was a steel joist? Is that considered 'solid'?

For reference, the FA contractor says that if the ceiling were to be left exposed, a fire alarm detector would be required between each joist (joists are 12" - 16" O.C.) which sounds ridiculous. The solution would be to put drywall over the entire ceiling so it could be considered a 'smooth ceiling'.

Thank you


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## cda (Jun 21, 2020)

Will have to look at 72, yes possibly the spacing between joists, may require smoke detectors in each pocket. 

For spacing, It should not matter what the joists are made of, as long as solid.


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## cda (Jun 21, 2020)

Outdated info


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## cda (Jun 21, 2020)

I am into pictures,

See if this helps


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## cda (Jun 21, 2020)

Why are smoke detectors being installed??

What type of occupancy??

Where is the requirement coming from


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## cda (Jun 21, 2020)

You have 2 feet deep joists??


If so looks like this applies::

Now just have to figure on the spacing between the joists

(2)
For ceilings with beam depths equal to or greater than 10 percent of the ceiling height (0.1 _H_), the following shall apply:


(a)
Where beam spacing is equal to or greater than 40 percent of the ceiling height (0.4 _H_), spot-type detectors shall be located on the ceiling in each beam pocket.


(b)
Where beam spacing is less than 40 percent of the ceiling height (0.4 _H_), the following shall be permitted for spot detectors:

i.
Smooth ceiling spacing in the direction parallel to the beams and at one-half smooth ceiling spacing in the direction perpendicular to the beams


ii.
Location of detectors either on the ceiling or on the bottom of the beams


Sorry I do not do math.


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>


Web or bar joists are not considered solid joists unless the top chord is over 4 in. (100 mm) deep, in which case, only the top chord is considered a ceiling obstruction.


3.3.40.4 Solid Joist Construction.
Ceilings that have solid structural or solid nonstructural members projecting down from the ceiling surface for a distance of more than 4 in. (100 mm) and spaced at intervals of 36 in. (910 mm) or less, center to center. (SIG-IDS)


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## eyan50495 (Jun 22, 2020)

cda said:


> Will have to look at 72, yes possibly the spacing between joists, may require smoke detectors in each pocket.
> 
> For spacing, It should not matter what the joists are made of, as long as solid.


That would make sense. I'd imagine one would treat the smoke detection of an open web steel joist and a wood truss the same vs. a wide flange or glu-lam.


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## cda (Jun 22, 2020)

eyan50495 said:


> That would make sense. I'd imagine one would treat the smoke detection of an open web steel joist and a wood truss the same vs. a wide flange or glu-lam.




Web or bar joists are not considered solid joists unless the top chord is over 4 in. (100 mm) deep, in which case, only the top chord is considered a ceiling obstruction.


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## mtlogcabin (Jun 22, 2020)

I-joist are manufactured with knock outs so use them and it is no longer "solid" webbing. Smoke will travel quickly through a 1 inch hole


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## ADAguy (Jun 22, 2020)

unsure about this comment?


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## eyan50495 (Jun 22, 2020)

cda said:


> Why are smoke detectors being installed??
> 
> What type of occupancy??
> 
> Where is the requirement coming from



The local fire ordinance from the county is stricter than the state code and requires Fire Alarms for all Mercantile type occupancies regardless of size. 

The fire marshal claims that NFPA 72 forces the building to either have a drywalled ceiling or, if left exposed, to have a fire alarm in between each and every joist in volumes based on squarefootage.

Trying to find that code section...


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## eyan50495 (Jun 22, 2020)

ADAguy said:


> unsure about this comment?



I guess he is saying that a wooden TJI can have large holes to allow ducts and other penetrations which would make it quite easy for smoke to pass through. I imagine that, that would actually help the fire alarms detect smoke?

I don't see a passage in NFPA 72 that talks about TJIs or goes into those level of details.


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## mtlogcabin (Jun 22, 2020)

https://www.techsupport.weyerhaeuse...8770-Is-there-a-top-or-bottom-to-a-TJI-joist-

Structurally, no, TJI® joists are manufactured without camber and with uniform properties regardless of orientation. However, the location of the pre-punched knockout holes will tend to be nearer one flange, so a builder might choose to install them with the holes down, to ease wiring or plumbing installations. Installing TJI® joists in a roof, with the holes near the top, might allow a builder to gain some cross ventilation from joist bay to joist bay.


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## cda (Jun 22, 2020)

eyan50495 said:


> The local fire ordinance from the county is stricter than the state code and requires Fire Alarms for all Mercantile type occupancies regardless of size.
> 
> The fire marshal claims that NFPA 72 forces the building to either have a drywalled ceiling or, if left exposed, to have a fire alarm in between each and every joist in volumes based on squarefootage.
> 
> Trying to find that code section...




Can you post the language requiring the fire alarm system


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## cda (Jun 22, 2020)

eyan50495 said:


> The local fire ordinance from the county is stricter than the state code and requires Fire Alarms for all Mercantile type occupancies regardless of size.
> 
> The fire marshal claims that NFPA 72 forces the building to either have a drywalled ceiling or, if left exposed, to have a fire alarm in between each and every joist in volumes based on squarefootage.
> 
> Trying to find that code section...




You cited it

From NFPA 72

If the joists are over a certain size deep and a certain size oc than, required in each cavity.

The same thing happens with fire sprinklers.


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## cda (Jun 22, 2020)

Does the building have a fire sprinkler system??!


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## cda (Jun 22, 2020)

eyan50495 said:


> I guess he is saying that a wooden TJI can have large holes to allow ducts and other penetrations which would make it quite easy for smoke to pass through. I imagine that, that would actually help the fire alarms detect smoke?
> 
> I don't see a passage in NFPA 72 that talks about TJIs or goes into those level of details.




Don’t guarantee this, so check the results 


Hit the sd beam tab and do the calculations



https://drive.google.com/file/d/15PEEYRVXup8u3ZABvtk2X843KYAN8Agv/view


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## FM William Burns (Jun 23, 2020)

The referenced code section being discussed and allegedly required NFPA 72 [17.7.3.2.4.2] and the sub-sectional criteria is correct. Don’t get hung up on the composite wood joist TJI v. solid. The material is considered solid (by mass) and as defined and if the area meets the sub-sectional criteria for detectors there will be one detector required for each pocket.

Read NFPA 72, 2019 [A7.7.3.2.4.2] which explains the rationale phenomenon for the detector coverage based on a potential fire’s heat plume and effects on smoke rise in pocketed beam construction.

The same phenomenon effects the levels of CO in a compartment fire but thats another discussion as is the fire effect on composite wood joist construction.......


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## eyan50495 (Jun 26, 2020)

OK UPDATE: There is certainly something wrong between what the FA Engineer is saying and what the FA Sub is claiming. 

Here's out situation: 2' Beams over a 10'-6" *clear *ceiling height. Not sure if you use clear ceiling height or ceiling height from top of finish to top of beam but I will use the more severe scenario. A 2' Beam would equate to 19% of the clear ceiling height.

County Fire Marshal points to NFPA 72. NFPA 72 17.7.3.2.4.2 states that a beam  >10% (0.1 H) but <40% (0.4 H) the following shall be permitted for spot detectors:

I. Smooth ceiling spacing in the direction parallel to the beams and at 1/2 smooth ceiling spacing in the direction perpendicular to the beams.
II. Location of detectors either on the ceiling or on the bottom of the beams.

The FA sub is claiming we need a spot-type detector located in EACH beam pocket but the NFPA says that only applies to >40%. Clearly he is misinformed?


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## cda (Jun 26, 2020)

eyan50495 said:


> OK UPDATE: There is certainly something wrong between what the FA Engineer is saying and what the FA Sub is claiming.
> 
> Here's out situation: 2' Beams over a 10'-6" *clear *ceiling height. Not sure if you use clear ceiling height or ceiling height from top of finish to top of beam but I will use the more severe scenario. A 2' Beam would equate to 19% of the clear ceiling height.
> 
> ...




I think you are missing an input

Distance between beams.


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## cda (Jun 26, 2020)

eyan50495 said:


> OK UPDATE: There is certainly something wrong between what the FA Engineer is saying and what the FA Sub is claiming.
> 
> Here's out situation: 2' Beams over a 10'-6" *clear *ceiling height. Not sure if you use clear ceiling height or ceiling height from top of finish to top of beam but I will use the more severe scenario. A 2' Beam would equate to 19% of the clear ceiling height.
> 
> ...



Will you post all the wording for the requirement!!!


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## cda (Jun 26, 2020)

eyan50495 said:


> OK UPDATE: There is certainly something wrong between what the FA Engineer is saying and what the FA Sub is claiming.
> 
> Here's out situation: 2' Beams over a 10'-6" *clear *ceiling height. Not sure if you use clear ceiling height or ceiling height from top of finish to top of beam but I will use the more severe scenario. A 2' Beam would equate to 19% of the clear ceiling height.
> 
> ...





Check pages 19-23

This appears to show an example of the year you are using


https://edwards-signals.com/files/3...e_and_Heat_Detectors_Application_Bulletin.pdf


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## eyan50495 (Jun 26, 2020)

cda said:


> I think you are missing an input
> 
> Distance between beams.


Yes! We are greater than 10% depth but since our spacing is 16" OC (less than 40% of ceiling height) this would still apply.


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## cda (Jun 26, 2020)

Ok so

10’6” to top of deck. 126 inches

2 foot deep beams      24 inches

Whoops wrong calc

ok here we go is this right??

ceiling 126 inches

Oc beam 192 inches 


40 % of 126 = 50.4 inches

So it appears the;;;;

*Greater*

(a)
Where beam spacing is equal to or greater than 40 percent of the ceiling height (0.4 _H_), spot-type detectors shall be located on the ceiling in each beam pocket.



16 foot on center

I am thinking without even seeing it or doing the math, yes required in each pocket.

What is the number of detectors the engineer wants??

What is the number of detectors the fire alarm company wants??


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## eyan50495 (Jun 26, 2020)

cda said:


> Ok so
> 
> 10’6” to top of deck
> 
> ...




*16 *inches* OC. 

The engineer is showing them 30' in one direction and 15' in the perpendicular. 

The fire alarm wants to put a fire alarm within *EACH *beam pocket *every 16 inches*.


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## eyan50495 (Jun 26, 2020)

FYI : https://www.nfpa.org/codes-and-stan...ds/list-of-codes-and-standards/detail?code=72

Page 108


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## cda (Jun 26, 2020)

eyan50495 said:


> *16 *inches* OC.
> 
> The engineer is showing them 30' in one direction and 15' in the perpendicular.
> 
> The fire alarm wants to put a fire alarm within *EACH *beam pocket *every 16 inches*.



Ok let take my shoes off again so I can do some trig


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## cda (Jun 26, 2020)

eyan50495 said:


> FYI : https://www.nfpa.org/codes-and-stan...ds/list-of-codes-and-standards/detail?code=72
> 
> Page 108





What I am asking is the code saying you have to put a fire alarm system in the building to begin with.

The section from the building/fire or amendments


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## cda (Jun 26, 2020)

Ok one more time

Ceiling 126 inches

Beam oc 16 INCHES

Equals 12.698 percent 


LESS THAN


So


Where beam spacing is less than 40 percent of the ceiling height (0.4 _H_), the following shall be permitted for spot detectors:

i.
Smooth ceiling spacing in the direction parallel to the beams and at one-half smooth ceiling spacing in the direction perpendicular to the beams


ii.
Location of detectors either on the ceiling or on the bottom of the beams


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## cda (Jun 26, 2020)

So have the engineer and fire alarm

Put the numbers on paper, just like me and 

Everyone set down in a locked room

Till it is figured out whose numbers are wrong and why


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## cda (Jun 26, 2020)

Still like to see the language requiring them in the first place


You are not doing delayed egress by chance??


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## eyan50495 (Jun 26, 2020)

cda said:


> Still like to see the language requiring them in the first place
> 
> 
> You are not doing delayed egress by chance??



Thank you CDA! Math on a Friday too.. no to the delayed egress.

IFC (907.2.7 Group M) says a Fire Alarm would _not _be necessary for this occupancy of this load (<500 occ total, <30 occ below, no 2nd story) but the local fire ordinance requires one.

Page: 227 refers to Fire Alarm  NFPA 72
Page: 249 section 18.11 requires a Fire Alarm for *ALL *new Mercantile Occ. 

Ordinance:
https://www.nassaucountyny.gov/DocumentCenter/View/17509/NCFPO_2016_rev_3-28-18?bidId=


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## cda (Jun 26, 2020)

Well talk about a code rewrite

And a 

Poor code rewrite

So I do not see anything in this passage that requires "smoke detection"???????????????

NFPA 72 is just an how to book. It does not dictate what has to be installed.!!!!!!!!

Is there another section in this novel that says smoke detection is required??

Fire Alarm System Required All new Mercantile Occupancies shall have a fire alarm system installed. The fire alarm system shall meet all the requirements of NFPA 72.18.11.3.1Existing Mercantile Occupancies where mammals (except horses, cattle, pigs or sheep), birds(except for chickens or other fowl used for food purposes), reptiles and/or amphibians are regularly kept or stored prior to their adoption, sale or gift as pets to the general public, shall have a fire alarm system installed by January 1,2018


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## cda (Jun 26, 2020)

Not sure how long this has been going on, or how someone would even figure out the cost of a job using this code:::

Ordinance:
https://www.nassaucountyny.gov/DocumentCenter/View/17509/NCFPO_2016_rev_3-28-18?bidId=


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## eyan50495 (Jun 26, 2020)

cda said:


> Not sure how long this has been going on, or how someone would even figure out the cost of a job using this code:::
> 
> Ordinance:
> https://www.nassaucountyny.gov/DocumentCenter/View/17509/NCFPO_2016_rev_3-28-18?bidId=



Yes, Nassau County's Fire Marshal's requirements is notoriously like a black hole. Other than the fact they say it is required in ALL new mercantile occupancies and per NFPA 72's locations, there isn't anything else on there.

Here in Nassau you have the option to file fire protection drawings 'regular' or 'expedited for a *fee*'. One gets you across the finish line in weeks and the other in many many months. No one does regular. It's the cost of playing ball here. Fun place to work!


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## cda (Jun 26, 2020)

eyan50495 said:


> Yes, Nassau County's Fire Marshal's requirements is notoriously like a black hole. Other than the fact they say it is required in ALL new mercantile occupancies and per NFPA 72's locations, there isn't anything else on there.
> 
> Here in Nassau you have the option to file fire protection drawings 'regular' or 'expedited for a *fee*'. One gets you across the finish line in weeks and the other in many many months. No one does regular. It's the cost of playing ball here. Fun place to work!






So where and when do these documents come into play???

"""""""""""""The 2015 International Fire and Building Codes""""""""""""""""""

Are they also adopted in the city/county where this store is???





https://www.nassaucountyny.gov/Docu...ow-Frequency-Alarm-Signal-Requirements?bidId=


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## eyan50495 (Jun 26, 2020)

cda said:


> So where and when do these documents come into play???
> 
> """""""""""""The 2015 International Fire and Building Codes""""""""""""""""""
> 
> ...



You're right... the county ordinance is very poorly written. I have to assume by "Fire Alarm" they are referring to both the Fire Alarm AND the Fire Detection. 

Regarding the IFC, I'm assuming that would come into play IF it was more restrictive. It doesn't seem like it is. I have found in this Fire Ordinance that they also refer to the New York State Uniform Fire Prevention and Building Code. Upon a quick search, that points to the Fire Code of NYS which also does not discuss fire detection in an M occupancy (it only discusses a fire alarm based on occupant load - I'm assuming this is based on IFC).

So go back to IF and WHERE these smoke detectors would be located one would assume it's via NFPA 72.

Still no clue where the FA sub is getting his information on needing to install a smoke detector within each joist bay. I'm waiting on more information from my FA engineer as I asked him the same set of questions. 

Further confused...


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## cda (Jun 27, 2020)

eyan50495 said:


> You're right... the county ordinance is very poorly written. I have to assume by "Fire Alarm" they are referring to both the Fire Alarm AND the Fire Detection.
> 
> Regarding the IFC, I'm assuming that would come into play IF it was more restrictive. It doesn't seem like it is. I have found in this Fire Ordinance that they also refer to the New York State Uniform Fire Prevention and Building Code. Upon a quick search, that points to the Fire Code of NYS which also does not discuss fire detection in an M occupancy (it only discusses a fire alarm based on occupant load - I'm assuming this is based on IFC).
> 
> ...



Under Ibc/ ifc if the building is sprinkled, no smoke detection required.

NFPA 72 does not dictate when to install


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## VillageInspector (Jul 2, 2020)

We are currently under the 2020 IFC here in NYS as of May 12, 2020. I would suggest you look at IFC Section 907 and in particular section 907.2.7 Group M. I think that might help you out.


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## cda (Jul 2, 2020)

VillageInspector said:


> We are currently under the 2020 IFC here in NYS as of May 12, 2020. I would suggest you look at IFC Section 907 and in particular section 907.2.7 Group M. I think that might help you out.




Finally a Voice of Reason, Common Sense, Freedom!!!


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