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Townhouse Fire-Rated Wall

R

rosegamble

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Joined
Jul 9, 2021
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87
Location
South Carolina
Hi All,

I've been hired to design a four-unit townhouse project - my first townhouse project.

I want to get this fire-rated wall right. The 2021 IRC allows two methods of creating this wall without a sprinkler: two 1-hour rated walls or one 2-hour common wall.

No interest in the one 2-hour common wall due to difficulties with penetrations and sound concerns.

See "Option 1" attached here, from National Gypsum. This is two 1-hour rated walls (rated from both sides I presume). I like this from a penetration perspective. All MEP penetrations are free to run in the stud cavities in each wall. However, my floor/ceiling joists are going to run the opposite way which presents some difficulty at the floor intersections (for example, how to make the interior side of the fire-rating continuous from top to bottom).

I found this "alternate" design online which is kind of neither method (two 1-hour rated walls or one 2-hour common wall) - see Option 2 attached here. It consolidates a 2 hour rating into the gypsum board panels in the center of the assembly, meaning the interior drywall is not rated and penetrations can move freely in these stud cavities. Since all the rating is happening in the center, my floor intersection issue is also negated.

Any thoughts? Would love to hear your experiences. Do you all have a UL approved detail you like to use? Struggling to find these online.
Option 1.JPG



Option 2.JPG
 
The first image is what I typically see for townhomes. The second image is a shaftliner panel system, more commonly used in commercial fire barrier applications - note that this would be a single, common-wall, two-hour rated wall assembly.

Each of the methods proposed has its own benefits and drawbacks. I'd say you should talk to the client and find out if the framer is comfortable with both methods. Be aware that the shaftliner panels require clips between the framed wall and the steel H-studs that burn/melt away during exposure. Thus, one unit may collapse without pulling the 2-hr wall down. Also be aware of total height, as sourcing of the H-studs can be difficult where listing requires continuous H-studs (no splice) from floor to underside of roof sheathing.

Going back to the first option... If the floor framing runs perpendicular to the rated wall, you can do one of the following:
  • Rated floor - fire rating is continuous if both wall and floor is rated
  • Ledger - balloon frame the wall and install a ledger wherein the 5/8" GWB is sandwiched between the studs and ledger
  • Stand-off hangers - use hangers that support the floor joists while allowing continuous GWB on the wall
 
classicT said:
The first image is what I typically see for townhomes. The second image is a shaftliner panel system, more commonly used in commercial fire barrier applications - note that this would be a single, common-wall, two-hour rated wall assembly.

Each of the methods proposed has its own benefits and drawbacks. I'd say you should talk to the client and find out if the framer is comfortable with both methods. Be aware that the shaftliner panels require clips between the framed wall and the steel H-studs that burn/melt away during exposure. Thus, one unit may collapse without pulling the 2-hr wall down. Also be aware of total height, as sourcing of the H-studs can be difficult where listing requires continuous H-studs (no splice) from floor to underside of roof sheathing.

Going back to the first option... If the floor framing runs perpendicular to the rated wall, you can do one of the following:
  • Rated floor - fire rating is continuous if both wall and floor is rated
  • Ledger - balloon frame the wall and install a ledger wherein the 5/8" GWB is sandwiched between the studs and ledger
  • Stand-off hangers - use hangers that support the floor joists while allowing continuous GWB on the wall
Click to expand...
Thanks so much. So in the "shaftliner" option (the second picture) this would technically be R302.2.2 the "common wall" method. R203.2.2 does not allow MEP penetrations in the stud cavity of a common wall. Would you agree that in the second picture however MEP penetrations would be fine in the stud cavities, since the rating is happening in the middle with no rating outside of the middle 2"?

Regarding the floor framing running perpendicular in the first option (first picture), this is great info. In the 1-hour rated floor scenario, wouldn't the blue area in the screenshot below be at risk however? Since floors get their rating from the ceiling membrane (rated membranes noted in red), the blue area doesn't feel "rated" technically? But maybe I'm being too literal.

1685652486056.png

Similarly, what about perpendicular walls in plan? Like so (see below). I guess the one-hour rating on the interior drywall would be interrupted at every perpendicular wall intersection unless you held the perpendicular framing off 5/8" to allow continuous Type X... framers would love that!

1685653065078.png
 
Hi all. In the intersections of the double 1-hour rated walls with the floors, even if the floor assemblies are 1 hour, the rim board feels exposed to me:

1688394311824.png

Do you think from a code perspective this is meeting the requires of R302.2.3 Continuity that the rating be continuous all the way up and down?
 
I would probably be ok with this, I think the rim board would take long enough to burn that it would not defeat the intent of the code to leave it exposed.
 
rosegamble said:
unless you held the perpendicular framing off 5/8" to allow continuous Type X... framers would love that!
Click to expand...
This is exactly what I would do, the commercial framers refer to that as a slap stud. Put the drywall on first and slap your stud right up against it.
 
rosegamble said:
Hi all. In the intersections of the double 1-hour rated walls with the floors, even if the floor assemblies are 1 hour, the rim board feels exposed to me:

View attachment 10924

Do you think from a code perspective this is meeting the requires of R302.2.3 Continuity that the rating be continuous all the way up and down?
Click to expand...
NOPE....One could argue IBC 703.2.2 though...

R302.2.1 Double Walls​

Each townhouse unit shall be separated from other townhouse units by two 1-hour fire-resistance-rated wall assemblies tested in accordance with ASTM E119, UL 263 or Section 703.2.2 of the International Building Code.
 
rosegamble said:
Hi All,

I've been hired to design a four-unit townhouse project - my first townhouse project.

I want to get this fire-rated wall right. The 2021 IRC allows two methods of creating this wall without a sprinkler: two 1-hour rated walls or one 2-hour common wall.

No interest in the one 2-hour common wall due to difficulties with penetrations and sound concerns.

See "Option 1" attached here, from National Gypsum. This is two 1-hour rated walls (rated from both sides I presume). I like this from a penetration perspective. All MEP penetrations are free to run in the stud cavities in each wall. However, my floor/ceiling joists are going to run the opposite way which presents some difficulty at the floor intersections (for example, how to make the interior side of the fire-rating continuous from top to bottom).

I found this "alternate" design online which is kind of neither method (two 1-hour rated walls or one 2-hour common wall) - see Option 2 attached here. It consolidates a 2 hour rating into the gypsum board panels in the center of the assembly, meaning the interior drywall is not rated and penetrations can move freely in these stud cavities. Since all the rating is happening in the center, my floor intersection issue is also negated.

Any thoughts? Would love to hear your experiences. Do you all have a UL approved detail you like to use? Struggling to find these online.
View attachment 10769



View attachment 10770
Click to expand...
Don't even attempt the two wall solution it doesn't work most of the times. Use the 2-hour shaft wall system.
 
chief-inspector said:
Don't even attempt the two wall solution it doesn't work most of the times. Use the 2-hour shaft wall system.
Click to expand...
The 2-hour shaft wall system becomes a bit odd however when the units jog in plan. For example, let's say the front wall of one unit is 5' proud of the the front wall of the next unit. The shaftliner method doesn't transition well to this condition.
 
rosegamble said:
The 2-hour shaft wall system becomes a bit odd however when the units jog in plan. For example, let's say the front wall of one unit is 5' proud of the the front wall of the next unit. The shaftliner method doesn't transition well to this condition.
Click to expand...
I never saw a problem with it since you can run it at any angle you want and it is self supporting.
 
chief-inspector said:
I never saw a problem with it since you can run it at any angle you want and it is self supporting.
Click to expand...
Which shaft wall system are you using that is self supporting? Every one I've seen uses aluminum melt-away clips on both side of the panel for lateral support. Hence, why shaftwalls do not work where the buildings are offset.
 
chief-inspector said:
I think they were USG but why can't you still attach the aluminum clips to a stud wall even if it runs at an angle?
Click to expand...
The shaftwall type assemblies (proper name is Area Separation Wall if following GA), require structural framing on both sides for lateral support.

If the front wall of one unit is 5-ft forward of the adjoining (think stair stepped in viewing in plan view), then the shaftwall only has framing on a single side. I have yet to see an GA ASW with that permitted in the listing.
 
classicT said:
The shaftwall type assemblies (proper name is Area Separation Wall if following GA), require structural framing on both sides for lateral support.

If the front wall of one unit is 5-ft forward of the adjoining (think stair stepped in viewing in plan view), then the shaftwall only has framing on a single side. I have yet to see an GA ASW with that permitted in the listing.
Click to expand...
Like this random internet image.

1698363493998.png
 
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