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Fire barriers at roof truss in wood construction

admiralArchArch

admiralArchArch

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Nov 30, 2018
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48
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middle earth
Regarding vertical continuity of a fire barrier at the roof (IBC 705.5), when you have roof truss/joists perpendicular to a fire barrier, in order to maintain continuity is it standard practice to design the fire barrier to bear the roof joist? Otherwise you have to frame the wall below the roof joist, the run the drywall above and between the joist up to the roof sheathing.
 
Would these sections come into play with your question?
IBC 2021
Sec 706-fire walls
Sec 706.1.1 party walls
Sec 706.6 vertical continuity
 
Yankee Chronicler said:
Please restate the question. As posted, it makes no sense.

Also, in my IBC 705.5 addresses exterior walls. What year are you using?
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Oops, typo. 2018 707.5 sorry about that.

I'm asking the practicality of building a fire barrier in wood framed construction to meet the intent of vertical continuity, what is the better detail, A or B?

1727875544995.png
 
The practical answer is that both of your solutions are -- for practical purposes -- impractical. B seems to require field modifying the trusses. I would be VERY skeptical about making that work.

You need a fire barrier, not a fire wall, correct? If you extend it to the underside of the deck, every member that penetrates it has to get a listed penetration seal. Why not terminate the fire barrier at the ceiling?
 
admiralArchArch said:
Oops, typo. 2018 707.5 sorry about that.

I'm asking the practicality of building a fire barrier in wood framed construction to meet the intent of vertical continuity, what is the better detail, A or B?

View attachment 14374
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B is how this is typically designed. A is if someone screwed up and forgot to add a detail for fire barriers.
If the AHJ is particular about the firestopping on the top chord bearing truss, you can use listed hangers designed to keep the truss outside of the gyp.
www.strongtie.com

DGT™

Ideal for multifamily construction, the DGT fire wall hanger is load tested and two-hour fire rated. It installs with a power nailer and features space to add two layers of 5/8" drywall after framing.
www.strongtie.com www.strongtie.com
 
admiralArchArch said:
n order to maintain continuity is it standard practice to design the fire barrier to bear the roof joist?
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Yes however you would have to use a mono-truss design Example "A" would never work.
Example "B" if you used a product similar to a Simpson DGHT hanger that could work
www.strongtie.com

DGHT™

Ideal for multifamily construction, the DGHT fire wall hanger is load tested and two-hour fire rated. It installs with a power nailer and features space to add two 5/8" drywall sheets after framing.
www.strongtie.com www.strongtie.com
1727888154635.png1727888686073.png
Using the mono truss approach is usually a shaft wall for the fire barrier and a 2x wall on each side of the shaft wall to support the trusses.
 
Yankee Chronicler said:
You need a fire barrier, not a fire wall, correct? If you extend it to the underside of the deck, every member that penetrates it has to get a listed penetration seal. Why not terminate the fire barrier at the ceiling?
Click to expand...

My apologies. Got fire barrier confused with fire partition. Fire barriers do have to extend to the underside of the deck above.
 
Paul Sweet said:
A is a constructibility nightmare. B might create several structural challenges below.
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Yes, I agree having to create bearing walls for all instances of fire barriers. Incidental uses, shafts, etc. Surely there's some middle ground here? I've gone and looked through a handful past wood framed projects and this has never been addressed.
 
mtlogcabin said:
Yes however you would have to use a mono-truss design Example "A" would never work.
Example "B" if you used a product similar to a Simpson DGHT hanger that could work
www.strongtie.com

DGHT™

Ideal for multifamily construction, the DGHT fire wall hanger is load tested and two-hour fire rated. It installs with a power nailer and features space to add two 5/8" drywall sheets after framing.
www.strongtie.com www.strongtie.com
View attachment 14382View attachment 14383
Using the mono truss approach is usually a shaft wall for the fire barrier and a 2x wall on each side of the shaft wall to support the trusses.
Click to expand...
What do you mean by monotruss?
 
admiralArchArch said:
Yes, I agree having to create bearing walls for all instances of fire barriers. Incidental uses, shafts, etc. Surely there's some middle ground here? I've gone and looked through a handful past wood framed projects and this has never been addressed.
Click to expand...

What do you mean by "middle ground"?

Let's begin at the beginning: what's the project, and why are fire barriers required? Is it for use group separations, or is it to create smaller fire areas within a building?

If fire barriers are required, then you need to remember that the building code is a MINIMUM standard for public safety. When you start with the MINIMUM standard and want to find ways to do less than that, my immediate question is, "Okay, you've decided that you don't want your building to be safe. Please explain just how unsafe you want your building to be."
 
admiralArchArch said:
What do you mean by monotruss?
Click to expand...
You would use a bearing wall supporting two individual mono trusses. A mono truss basically slopes in one direction. Typically this old detail is not used anymore around here. Contractors will is a shaft wall for the 2 hour fire barrier requirement.


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Yankee Chronicler said:
What do you mean by "middle ground"?

Let's begin at the beginning: what's the project, and why are fire barriers required? Is it for use group separations, or is it to create smaller fire areas within a building?

If fire barriers are required, then you need to remember that the building code is a MINIMUM standard for public safety. When you start with the MINIMUM standard and want to find ways to do less than that, my immediate question is, "Okay, you've decided that you don't want your building to be safe. Please explain just how unsafe you want your building to be."
Click to expand...
I'm not trying to cut corners, I'm just trying to understand how to properly detail a fire barrier in multifloor R-2 wood construction (or any wood construction) that meets the intent of the code. Fire barriers required for shair shafts, incidentintal uses, etc. Not using to create fire area separations, but I guess the same question would apply if I was.

Middle ground as in detailing between my two examples.
 
Yankee Chronicler said:
I certainly would not allow a wood truss (or a dimension lumber floor joist) to penetrate an exit stair enclosure. That's a no-no.
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Not anymore as too many stupid people in the code process....

1023.5​

Penetrations into or through interior exit stairways and ramps are prohibited except for the following:

  1. 1.Equipment and ductwork necessary for independent ventilation or pressurization.
  2. 2.Fire protection systems.
  3. 3.Security systems.
  4. 4.Two-way communication systems.
  5. 5.Electrical raceway for fire department communication systems.
  6. 6.Electrical raceway serving the interior exit stairway and ramp and terminating at a steel box not exceeding 16 square inches (0.010 m2).
  7. 7.Structural elements supporting the interior exit stairway or ramp or enclosure, such as beams or joists.
Such penetrations shall be protected in accordance with Section 714. There shall not be penetrations or communication openings, whether protected or not, between adjacent interior exit stairways and ramps.

Exception: Membrane penetrations shall be permitted on the outside of the interior exit stairway and ramp. Such penetrations shall be protected in accordance with Section 714.4.2.

So not only can you penetrate it...You can run the open web truss right through it and cantilever it as the stair landing. And when you use an R system with no sprinklers in the floor, it can collapse and destroy egress in a floor fire before anyone even knows there is a problem, just like the roof assembly........And then the next discussion will be whether or not you actually need to protect it as in VA it will be a 1 hour assembly "penetrating" the stair........
 
We always do A, with a UL listed/designed fire blocking product at any penetrations.

It is not realistic or practical to reengineer the roof framing system like B. Most building would require demolishing the entire roof structure in the area of work to make that happen, which would be an exorbitant cost.
 
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