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Fire Separations Pt3 vs Pt9

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Plumb-bob

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Requirements for continuity of fire separations is very clear in Pt3- vertical separations must be carried to the underside of roof or floor deck, or be intersected by a horizontal separation of the same rating:
1698676231731.png
Pt9 is much less clear-
1698676293917.png

In a 2 storey townhouse (Pt9), where the party wall separation is interrupted by the floor system, I interpret the requirement for either 1) the separation to be continuous to the underside of the floor sheathing, or 2) the first floor ceiling to be rated.
In this case the party wall is a bearing wall, with the ijoists run perpendicular to, and bearing on, the party wall.

Anybody see this differently?
 
The way we interpret it, you can only terminate the fire separation at a floor or ceiling is if it has an equivalent fire rating. In your townhouse example, the only thing rated is the demising wall, so the rating must be maintained.

The issue I find is that people approach this problem in reverse. They decide what the construction is, where floor joists are being run, and then try to tackle the continuity of the fire separation. Ineveitably the continuity of the fire separation is compromised by this approach. A better way to approach it would be that the fire separation exists first. Now we figure out how/where we are running the floor joists. This is what 9.10.9.2.(3) is indicating.

When we started to dig into this more aggressively, most developers changed to only run their joists and trusses parallel to the fire separation. The fire separation can then obviously be constructed completely continuous.
 
tmurray said:
When we started to dig into this more aggressively, most developers changed to only run their joists and trusses parallel to the fire separation. The fire separation can then obviously be constructed completely continuous.
Click to expand...
But they were doing it that way for 30 years.....:rolleyes:
 
I told them they can rate the 1st floor ceiling, or get some kid on a jig saw to start cutting 5/8 type X in the ijoist profile to fill in the box ends to keep the vertical separation continuous.
 
tmurray said:
The issue I find is that people approach this problem in reverse. They decide what the construction is, where floor joists are being run, and then try to tackle the continuity of the fire separation. Ineveitably the continuity of the fire separation is compromised by this approach. A better way to approach it would be that the fire separation exists first. Now we figure out how/where we are running the floor joists. This is what 9.10.9.2.(3) is indicating.
Click to expand...

This is why virtually every townhouse-type structure I've seen built in the last 20+ years has used the U.S. Gypsum fire separation assembly as the rated party wall between units, which then allows the units themselves to be framed in either direction without affecting the integrity or the rating of the party wall.

I also know first-hand that it's an effective fire barrier. Back around 2008 or 2009, we had a 300+ condo being developed in town -- all townhouse units. One weekend, the tapers had just completed an end unit, and they left a salamander running to ensure that the taping compound dried over the weekend. Something went wrong, and the unit caught fire. The fire unit burned completely, leaving just a basement full of wet ashes and a few charred remnants of framing. The adjacent unit suffered only minor water damage.
 
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