Calculate 4 or 8 Sprinkler for TJI Rated Assembly?

3/23/2023

Here's a twist on the 9/28/2021 post regarding 4 or 8 sprinkler residential calcs (link here):

Given an NFPA 13-2016 fully sprinklered wood framed apartment project, with residential sprinklers, and unsprinklered combustible concealed TJI spaces between floors, per Section 8.15.1.2.6 similar to this system:

Spaces between joists are blocked into 160 cubic feet using the same TJI material.

Spaces are not firestopped with a minimum ½” drywall on the sides of certain TJI’s into 160 cubic foot spaces.

Since the 2013 NFPA-13 came out, my understanding has been that unless we were to install ½” gypsum on the side of every few TJI’s to subdivide into 160 cubic foot spaces, an 8-sprinkler calculation is required in the occupied spaces above and below this assembly.

Some have argued that since it’s a 1-hour assembly, a 4 sprinkler calculation is fine since that’s greater than a 30 minute barrier (light hazard water supply duration) as discussed in 11.2.3.1.5.1 (B). However, Annex A11.2.3.1.5.1 seems support the 8 sprinkler calculation because the assembly is the qualifying non-sprinklered area.

However, in the above example, a portion of that assembly in itself provides a 30 minute barrier. It’s a 1 hour rated assembly but In this case, the bottom is 2 layers of Type X which in itself is greater than a 30 minute barrier.

I’m guessing that the top with tongue and groove sheeting and 1” of gypsum would also provide at least a 30 minute barrier.

Would the NFPA 13 sprinklered dwelling spaces above and below this (allowed) non-sprinklered floor/ceiling space require a 4 or 8 sprinkler calculation?

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4 Comments

Dan Wilder

3/23/2023 08:58:56 am

The way I ready the 13-2022 Edition, you are still required to provide the 8 sprinkler calculation but you would not have to extend that 8 sprinkler calculation (or other design method) to the adjacent areas that do not have unsprinklered areas (it would go back to the 4 sprinkler design)

19.3.1.2 *
Unless the requirements of 19.2.3.1.5.2 are met for buildings having unsprinklered combustible concealed spaces, as described in 9.2.1 and 9.3.18, the minimum design area of sprinkler operation for that portion of the building shall be eight sprinklers.

19.3.1.2.1 *
The design area of eight sprinklers shall be applied only to the portion of the residential sprinklers that are adjacent to the qualifying combustible concealed space.

A.19.3.1.2.1
In order for the minimum eight sprinkler requirement for the size of the remote area to not be extended to the adjacent area, the qualifying concealed space must be separated by the entire fire-rated assembly. Such assemblies often have combustible structural members separating the exterior membranes that can create a concealed combustible space that can qualify for omitting sprinkler protection. If the fire-rated assembly is the qualifying concealed space, an interior fire would greatly reduce the assigned fire-rated duration.

19.3.1.2.2
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.

Refer to the commentary following 19.2.3.1.5.1 for information on the separation from the adjacent area.

(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.

The intention of 19.2.3.1.5.1 is not to permit the omission of sprinklers from combustible concealed spaces but, rather, to compensate for the anticipated delay of sprinkler operation for a fire originating in an unprotected, combustible concealed space. As noted, 9.2.1 describes the conditions under which sprinklers do not have to be installed in concealed spaces.

The 3000 ft2 (280 m2) area of operation requirement also applies to the room design method and supersedes limiting the remote area based only on room size. This requirement is further clarified by 19.2.3.2.8.2, whereby the 3000 ft2 (280 m2) requirement is applied after all other area modifications have been made.

The requirement for buildings having an unprotected, combustible concealed space is that they must have a 3000 ft2 (280 m2) remote area. This requirement does not apply to the entire building but only to the portion of the building adjacent to the unprotected, combustible concealed space. The term adjacent refers not only to the area horizontally on the floor of interest but also to the portion of the floors immediately above and below the unprotected, combustible concealed space, unless the adjacent area is separated by fire-rated construction. If the fire-rated assembly itself creates an unprotected, combustible concealed space, the adjacent portions of the building are still required to apply a 3000 ft2 (280 m2) area of operation.

Todd E Wyatt

3/23/2023 09:34:53 am

Determining the fire-resistance rating (FRR) of a tested assembly or individual components such as gypsum board should be based on the adopted Code (e.g. 2021 IBC). The FRR “of building elements, components or assemblies“ are determined by 703.2.1 Tested Assemblies or 703.2.2 Analytical Methods “without the use of automatic sprinklers or any other fire suppression system” or by 703.2.3 Approved Alternate Method.

Based on your statement (I’m guessing that the top with tongue and groove sheeting and 1” of gypsum would also provide at least a 30 minute barrier.), you’d need to review “Section 722 Calculated Fire Resistance” to determine its FRR.

If you want to let a testing agency (e.g. UL) determine the FRR, review “Fire-resistance Ratings - ANSI/UL 263”. This includes a NUMBERING SYSTEM FOR FIRE-RATED ASSEMBLIES based on the TYPES OF PROTECTION.

UL 263 includes “Groups of Construction” such as “Floors-Ceilings”
A or B - Concrete and Cellular Steel Floor
C - Glazing Systems
D, E or F - Concrete and Steel Floor Units
G or H - Concrete and Steel Joists
I Protective Membranes or Ceiling Membranes
J or K Concrete
L or M - Wood Joist or Combination Wood and Steel Assemblies

This condition would be “L or M - Wood Joist or Combination Wood and Steel Assemblies” with a “Membrane Protection” of “500-599 Gypsum Board”. “L5##” would be comparable assemblies.

3/23/2023 09:35:33 am

REFERENCES

2021 IBC
Chapter 7 Fire and Smoke Protection Features
User note:
About this chapter: Chapter 7 provides detailed requirements for fire-resistance-rated construction, including structural members, walls, partitions and horizontal assemblies. Other portions of the code describe where certain fire-resistance-rated elements are required. This chapter specifies how these elements are constructed, how openings in walls and partitions are protected and how penetrations of such elements are protected.
Section 701 General
701.1 Scope
The provisions of this chapter shall govern the materials, systems and assemblies used for structural fire resistance and fire-resistance-rated construction separation of adjacent spaces to safeguard against the spread of fire and smoke within a building and the spread of fire to or from buildings.

Section 722 Calculated Fire Resistance
722.1 General
The provisions of this section contain procedures by which the fire resistance of specific materials or combinations of materials is established by calculations. These procedures apply only to the information contained in this section and shall not be otherwise used. The calculated fire resistance of specific materials or combinations of materials shall be established by one of the following:
1. Concrete, concrete masonry and clay masonry assemblies shall be permitted in accordance with ACI 216.1/TMS 0216.
2. Precast and precast, prestressed concrete assemblies shall be permitted in accordance with PCI 124.
3. Steel assemblies shall be permitted in accordance with Chapter 5 of ASCE 29.
4. Exposed wood members and wood decking shall be permitted in accordance with Chapter 16 of ANSI/AWC NDS.

722.6 Wood Assemblies
The provisions of this section contain procedures by which the fire-resistance ratings of wood assemblies are established by calculations.
722.6.1 General
This section contains procedures for calculating the fire-resistance ratings of walls, floor/ceiling and roof/ceiling assemblies based in part on the standard method of testing referenced in Section 703.2.
722.6.1.1 Maximum Fire-Resistance Rating
Fire-resistance ratings calculated for assemblies using the methods in Section 722.6 shall be limited to not more than 1 hour.
722.6.1.2 Dissimilar Membranes
Where dissimilar membranes are used on a wall assembly that requires consideration of fire exposure from both sides, the calculation shall be made from the least fire-resistant (weaker) side.
722.6.2 Walls, Floors and Roofs
These procedures apply to both load-bearing and nonload-bearing assemblies.

TABLE 722.6.2(1) TIME ASSIGNED TO WALLBOARD MEMBRANES
DESCRIPTION OF FINISH TIME (minutes)
3/8-inch wood structural panel bonded with exterior glue 5
15/32-inch wood structural panel bonded with exterior glue 10
19/32-inch wood structural panel bonded with exterior glue 15
3/8-inch gypsum wallboard 10
1/2-inch gypsum wallboard 15
5/8-inch gypsum wallboard 30
1/2-inch Type X gypsum wallboard 25
5/8-inch Type X gypsum wallboard 40
Double 3/8-inch gypsum wallboard 25
1/2-inch + 3/8-inch gypsum wallboard 35
Double 1/2-inch gypsum wallboard 40
a. These values apply only where membranes are installed on framing members that are spaced 16 inches o.c. or less.
b. Gypsum wallboard installed over framing or furring shall be installed so that all edges are supported, except 5/8-inch Type X gypsum wallboard shall be permitted to be installed horizontally with the horizontal joints staggered 24 inches each side and unsupported but finished.
c. On wood frame floor/ceiling or roof/ceiling assemblies, gypsum board shall be installed with the long dimension perpendicular to framing members and shall have all joints finished.
d. The membrane on the unexposed side shall not be included in determining the fire resistance of the assembly. Where dissimilar membranes are used on a wall assembly, the calculation shall be made from the least fire-resistant (weaker) side.
e. The time assigned is not a finished rating.

Eric R

3/23/2023 09:44:15 am

This can be tricky as it can go either way really. My default answer would be that both areas above and below should have the extended design area based on A.19.3.1.2.1 that Dan posted above.

Now you could work around this by documenting that the membrane sections of the rated assembly both above and below meet the 30 minute provision, but remember that a rating is not defined simply by the thickness of the gypsum. The fastener arrangements, offsetting of joints, and any through penetrations of that membrane would all need to be considered. It can be done, but taking on the responsibility to make sure that it's designed properly when it goes beyond a simple UL diagram is not something I would want to take on if I'm simply providing sprinkler design services.

I think it stinks that the arrangement that allows you to exclude sprinklers, and the arrangement to exclude sprinklers and not increase the design area aren't correlated (even though it may be backed up by good reasoning). Trying to explain to an architect that a certain framing arrangement allows me to exempt sprinklers, but then saying they can't use it without adding in the extra gypsum layer ever couple joists or my flow rate suddenly doubles is always a battle.

Tell the architect to fill the TJI bays with insulation. At least that's always how this problem ends up being resolved when I have to deal with it.

Calculate 4 or 8 Sprinkler for TJI Rated Assembly?

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