Fire rating for stacked duplexes on the same property

[Shams Gannon]

Am I reading the IRC correctly that "Walls of dwellings... on the same lot" are exempt from Table R302.1(1)?

I have a project which may include two or more stacked duplexes, three stories each, with 4' between each building. My intuition was to provide a 1hr exterior wall where they faced each other. However, is this fire rating not required as they are dwelling units on the same lot?

I should add - since we're stacking the units we'll have the floor assembly and supporting walls of the lower unit fire-rated.

 

[e hilton]

Is a dwelling defined as occupied by one family unit?

 

[Mr. Inspector]

[RB] DWELLING. Any building that contains one or two
dwelling units used, intended, or designed to be built, used,
rented, leased, let or hired out to be occupied, or that are
occupied for living purposes.
[RB] DWELLING UNIT. A single unit providing complete
independent living facilities for one or more persons, including
permanent provisions for living, sleeping, eating, cooking
and sanitation. For the definition applicable in Chapter 11,
see Section N1101.6.

The buildings are dwellings not dwelling units so you cannot use the exception in 2018 IRC.

R302.1 Exterior walls. Construction, projections, openings
and penetrations of exterior walls of dwellings and accessory
buildings shall comply with Table R302.1(1); or dwellings
equipped throughout with an automatic sprinkler system
installed in accordance with Section P2904 shall comply
with Table R302.1(2).
Exceptions:
1. Walls, projections, openings or penetrations in walls
perpendicular to the line used to determine the fire
separation distance.
2. Walls of individual dwelling units and their accessory
structures located on the same lot.
3. Detached tool sheds and storage sheds, playhouses
and similar structures exempted from permits are
not required to provide wall protection based on
location on the lot. Projections beyond the exterior
wall shall not extend over the lot line.
4. Detached garages accessory to a dwelling located
within 2 feet (610 mm) of a lot line are permitted to
have roof eave projections not exceeding 4 inches
(102 mm).
5. Foundation vents installed in compliance with this
code are permitted.