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Townhouse floor sheathing question

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palikona

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Jan 8, 2022
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65
Location
Colorado
Hi,
This question came up today with my structural engineer on a townhouse project I’m designing: can the floor sheathing be continuous through the building of 4 units?

I have a double wall between each units, with 2x6 framing for each unit’s demising wall and a 1” gap between the framing. Based on how I read the code, I think the floor sheathing needs that gap as well, so the structure is continuous from bottom to roof? Am I reading that right? Any help is appreciated.
 
For structural purposes, the sheathing should run continuously through the fire wall.
For sound and fire, it should stop at the fire wall.

Structural Trumps all. Run it through
 
The CABO code always required structural independence for townhouse construction. It wasn't until the IRC that permitted the wall and roof sheathing to be continuos across the common walls. Running floor sheathing continuos through the units does not meet the requirement for structural independence in the IRC.

R302.2.3 Continuity.
The fire-resistance-rated wall or assembly separating townhouses shall be continuous from the foundation to the underside of the roof sheathing, deck or slab. The fire-resistance rating shall extend the full length of the wall or assembly, including wall extensions through and separating attached enclosed accessory structures.

R302.2.6 Structural independence.
Each individual townhouse shall be structurally independent.

Exceptions:

1. Foundations supporting exterior walls or common walls.

2. Structural roof and wall sheathing from each unit fastened to the common wall framing.

3. Nonstructural wall and roof coverings.

4. Flashing at termination of roof covering over common wall.

5. Townhouses separated by a common wall as provided in Section R302.2.2, Item 1 or 2.

R302.2.2 Common walls.
Common walls separating townhouses shall be assigned a fire-resistance rating in accordance with Item 1 or 2. The common wall shared by two townhouses shall be constructed without plumbing or mechanical equipment, ducts or vents in the cavity of the common wall. The wall shall be rated for fire exposure from both sides and shall extend to and be tight against exterior walls and the underside of the roof sheathing
 
I was going of the definition of fire wall in the 2015 IBC FIRE WALL. A fire-resistance-rated wall having protected openings, which restricts the spread of fire and extends continuously from the foundation to or through the roof, with sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall.

Follow on question, what is the rated assembly being used to construct the wall and does the rated assembly allow the floor system to got through it?
 
mark handler said:
For structural purposes, the sheathing should run continuously through the fire wall.
For sound and fire, it should stop at the fire wall.

Structural Trumps all. Run it through
Click to expand...

Nope. The townhouse unit separation has to be an absolute separation. The floor sheathing CANNOT run through the separation wall.

We saw this in action at my previous job. Townhouse complex under construction. Toward the end, the sheetrockers left a salamander running over a weekend to help dry the taping compound so they could apply the next coat first thing on Monday. Something happened, and the end unit caught fire. The fire separation was the USG separation assembly. It worked. The end unit burned down completely, leaving a pile of ashes in the basement. The adjacent unit had slight water damage from the fire department.

Details, from the source:

1712888404641.png
 
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