# R302.3 Side-by-Side 2-Story Duplex



## Self-Certification (Apr 20, 2021)

So, while I'm waiting for an ICC interpretation ... has anyone run into this:

R302.3 states that "...wall assemblies shall extend from the foundation to the underside of the roof sheathing."

In a current project, there is a side-by-side two-family, two-story structure.  Sprinklers not required/provided.  Type V construction, slab-on-grade.  They're utilizing a set (double) of GA WP-3605 1-hour assemblies with a 1"-2" airspace in between.

Here's the main point:  The floor sheathing is continuous across the separation wall for a structural purpose (diaphragm).  In other words, the WP-3605 wall assembly extends from the slab to the underside of the floor sheathing, and then again from the top of the floor sheathing to the underside of the roof sheathing.

FIRST question:  Does that code section mean to imply a *continuous* wall assembly??

If so, it seems to be in conflict with the townhouse continuity requirement of R302.2.3, where it says that the wall assembly "shall be continuous from the foundation to the underside of the roof sheathing, deck or slab".  Not to mention, R302.2.3 seems to make a more broad allowance for the upper termination (not just roof sheathing).

SECOND question:  Would R302.3, Exception #2 apply to the floor/ceiling "attic" space as it would to the roof/ceiling attic space??


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## fatboy (Apr 20, 2021)

Yes, continuous, uninterrupted. One can fall/burn down, and not disturb the other.


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## Self-Certification (Apr 20, 2021)

fatboy said:


> Yes, continuous, uninterrupted. One can fall/burn down, and not disturb the other.


Where does it require two-family dwellings to have the same structural independence as townhouses??


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## cda (Apr 20, 2021)

Self-Certification said:


> Where does it require two-family dwellings to have the same structural independence as townhouses??



Not required in townhouses


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## cda (Apr 20, 2021)

Self-Certification said:


> So, while I'm waiting for an ICC interpretation ... has anyone run into this:
> 
> R302.3 states that "...wall assemblies shall extend from the foundation to the underside of the roof sheathing."
> 
> ...



Seems like you are interrupting the one hour wall,, with the floor??

How do you maintain the one hour assembly where the floor intersects??


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## Self-Certification (Apr 20, 2021)

cda said:


> Not required in townhouses


R302.2.6 doesn't apply to townhouses?


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## Self-Certification (Apr 20, 2021)

cda said:


> Seems like you are interrupting the one hour wall,, with the floor??
> 
> How do you maintain the one hour assembly where the floor intersects??


Possibly.  Floor sheathing only is crossing the 1-hour partition.

Cross-referencing the 2018 IBC 708.4.  Separation walls in Group R occupancies are to have fire partitions that extend from the top of the foundation and be attached to the underside of the *floor* or roof sheathing above.


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## cda (Apr 20, 2021)

Ok use to sprinklers 

Make it two hour and no problem

Except the floor intersecting


R302.2.2 Common Walls


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## steveray (Apr 21, 2021)

The differences are subtle.....

R302.3 Two-family dwellings. Dwelling units in two-family
dwellings shall be separated from each other by wall and
floor assemblies having not less than a 1-hour fire-resistance
rating where tested in accordance with ASTM E 119 or UL
263. Fire-resistance-rated floor/ceiling and wall assemblies
shall extend to and be tight against the exterior wall, and wall
assemblies shall extend from the foundation to the underside
of the roof sheathing.

R302.2.1 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.

And really with that section it is trying to say that it can't stop "at the unit" at all in the case of a TH, but with the exception for 2 fam...


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## Sifu (Apr 21, 2021)

Do you mean this?






As opposed to this?


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## ADAguy (Apr 29, 2021)

Solid Blocking appears to be the key


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## redeyedfly (Apr 29, 2021)

fatboy said:


> Yes, continuous, uninterrupted. One can fall/burn down, and not disturb the other.


No, that's for townhouses R302.2.  R302.3 for two-family does not require structural independence.  How would you build an up/down duplex structurally independent?



cda said:


> Not required in townhouses



Structural independence IS required in townhouses because you have a lot line running between the two structurally independent walls.  They are single family attached.


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## ADAguy (Apr 29, 2021)

Point made


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