Fire Alarms on Wood TJI Ceiling (Exposed)

[eyan50495]

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

 

[cda]

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.

 

[cda]

Outdated info

 

[cda]

I am into pictures,

See if this helps

 

[cda]

Why are smoke detectors being installed??

What type of occupancy??

Where is the requirement coming from

 

[cda]

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:

1. (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.
   
   
2. (b)
   Where beam spacing is less than 40 percent of the ceiling height (0.4 H), the following shall be permitted for spot detectors:
   
   1. 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
      
      
   2. 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)

 

[eyan50495]

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.

 

[cda]

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.

 

[mtlogcabin]

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

 

[ADAguy]

unsure about this comment?

 

[eyan50495]

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...

 

[eyan50495]

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.

 

[mtlogcabin]

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.

 

[cda]

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

 

[cda]

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.

 

[cda]

Does the building have a fire sprinkler system??!

 

[cda]

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

 

[FM William Burns]

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.......

 

[eyan50495]

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?

 

[cda]

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?

I think you are missing an input

Distance between beams.

 

[cda]

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?

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

 

[cda]

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?

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

 

[eyan50495]

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.

 

[cda]

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??