Firewall question

Does a fire wall in the attic of a duplex have to be taped completely? Is one layer of 5/8 drywall acceptible between duplex walls in the attic?

Yes. All openings (including drywall joints) must be sealed with a rated material. As to the question of one layer of drywall; I think it depends when the home/condo was built and to what standard or code. I would think more than one layer of drywall would be required (and would provide better protection).

Generally… depends. What does your local AHJ say?

Typically (in my area)… as long as the drywall is fire rated, and individual sheets butt up together, and these joints fall solidly onto framing… it is okey-dokey without being taped/mudded.

Fed may be different from State, which may be different from County, which may be different from City.

Get’s real confusing around here at times!

BTW… isn’t Canada smoke/vapor rated as opposed to fire rated? Or is it both? That may be another difference between our countries codes.

That is for a garage attached to and part of a single dwelling unit. No fire separation required. Must have a self closing airtight door from house to garage and no door from a bedroom to garage.

Depending on the arrangement with other occupancies (mercatile, etc)/# of stories, various requirements for fire separations between residential units/others apply with fire resistant ratings from 45 min to 2 hours.

Not applicable here, but good to know the difference between what’s required for a townhouse vs. a duplex.

"Definition: TOWNHOUSE. A single-family dwelling unit constructed in
a group of three or more attached units in which each unit
extends from foundation to roof and with a yard or public way
on at least two sides.

2009 IRC R302.2 Townhouses. Each townhouse shall be considered a
separate building
and **shall be separated by fire-resistance-
rated wall assemblies meeting the requirements of Section
R302.1 for exterior walls.**Exception: A common 1-hour fire-resistance-rated wall
assembly tested in accordance with ASTME 119 or UL 263
is permitted for townhouses if such walls do not contain
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.
Electrical installations shall be installed in accordance
with Chapters 34 through 43. Penetrations of electrical outlet
boxes shall be in accordance with Section R302.4.
**Commentary: **The application of this section has its basis in the exterior
wall requirements found in Section R302.1 that
deal with the building’s location on the lot. The definition
of a townhouse in Section R202 should be reviewed,
as well as the requirement for structural independence
in Section R302.2.4. In general, because
the “exterior wall” of the townhouse is essentially being
constructed with no fire separation distance where one
townhouse adjoins another, the code requires, by Section
R302.1, that the wall have not less than a 1-hour
fire-resistance rating. The adjacent townhouse would
have the same requirement. Therefore, the general requirement
at this location (based on Sections R302.1
and R302.3) would be that each townhouse has its
own “exterior wall.” This would result in the construction
of two separate 1-hour walls located side by side
where one townhouse adjoins another.

Because of the difficulties involved in construction
and the potential for unnecessary duplication, the exception
offers an alternative to the two separate 1-hour
walls by permitting the construction of a shared or
“common” 2-hour-rated wall between the townhouses.

See Commentary Figure R302.2 for an illustration of
the two separate 1-hour walls and the common 2-hour
wall. This exception has its basis in the actions of
many building officials who permit this type of common
wall as an alternative method of construction using
provisions similar to those found in Section R104.11.
Because the common wall has the potential to create
an interconnection between the adjacent dwelling
units and reduce the clear separation that would exist
if two separate walls were constructed, the code
places limits on services being located within the wall.
This exception does not permit the inclusion of any
type of plumbing, mechanical equipment, ducts or
vents within the cavity of the common wall
. This prohibition
is applicable even if the penetrations or openings
are protected by the penetration provisions of
Section R302.4 or if a damper is installed in the duct or
vent. The prohibition on plumbing includes all types of
plumbing materials and systems, as well as water supply
and drainage piping of either combustible or
noncombustible materials. However, the exception
permits the cavity of the wall to be used for electrical
installations if they comply with the electrical provisions
of the code and the penetrations are properly

"2009 IRC R302.3 Two-family dwellings. Dwelling units in two-family
dwellings shall be separated from each other by wall and/or
floor assemblies having not less than a 1-hour fire-resistance
rating when tested in accordance with ASTME 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.Exceptions:

  1. A fire-resistance rating of 1/2 hour shall be permitted in
    buildings equipped throughout with an automatic sprinkler
    system installed in accordance with NFPA 13.

2. Wall assemblies need not extend through attic spaces
when the ceiling is protected by not less than 5/8-inch
(15.9 mm) Type X gypsum board and an attic draft
stop constructed as specified in Section R302.12.1 is
provided above and along the wall assembly separating
the dwellings. The structural framing supporting
the ceiling shall also be protected by not less than
1/2-inch (12.7 mm) gypsum board or equivalent.

**Commentary: **Most of the nation’s fires occur in residential buildings,
particularly one- and two-family dwellings. These fires
account for more than 80 percent of all deaths from fire
in residential uses (including hotels, apartments, dormitories,
etc.) and about two-thirds of all fire fatalities in
any type of building. One- and two-family dwellings also
account for more than 80 percent of residential property
losses and more than one-half of all property losses
from fire. Despite this poor fire record, there is
wide-spread resistance to mandating much in the way
of fire protection systems or methods because of our
society’s belief that people’s homes are their castles.
This viewpoint has limited the types of protection that
are imposed on these private homes to the installation
of smoke alarms and the more recent requirement of
dwelling unit separation. Section R302.3 provides a
separation for protection of the occupants of one dwelling
unit from the actions of their neighbor. The requirements
of this section pertain to any structure regulated
by the code other than a single-family dwelling unit. To
accomplish this protection, the code addresses separation
between the units, structural support and any openings
or penetrations of the separation.

Depending on the layout of the various dwelling units,
Section R302.3 requires that the walls and/or floor assemblies
that divide one dwelling unit from the adjacent
unit is of at least 1-hour fire-resistant construction
. See
Commentary Figure R302.3 for examples of the separation.
The separation rating is to be determined by either
ASTM E 119 or UL 263, which is the normal test
used for determining fire resistance. Many tested assemblies
are available for use in these locations. The
provisions of the section also address the continuity of
the separation, so that one dwelling unit is completely
divided from the other
. The horizontal aspect of the separation,
which requires that the assemblies extend to
and be tight against the exterior wall, is not difficult to
comply with. It is most likely the vertical aspect (continuing
a wall assembly to the underside of the roof sheathing)
that will require some detailed planning, careful
construction and careful inspection for the units to be

Exception 1 grants a reduction in the required separation
for those cases in which the building is equipped
with an automatic sprinkler system. In these cases, a
rating of 1/2 hour is permitted versus a 1-hour fire-resistance
rating. The sprinkler system must be “installed in
accordance with NFPA 13,” and is to be installed
“throughout” the building. The type of sprinkler system
used must meet NFPA 13 and may not be installed to
either the NFPA 13D or 13R, even though those two
standards do address certain types of residential uses.
The word “throughout” requires that the sprinkler system
be installed in all portions of both dwelling units
and any common spaces. The provisions of NFPA 13
that permit omitting sprinklers in certain areas, such as
small concealed spaces, are applicable. Therefore,
the provision requires a complying sprinkler system
“throughout” the building (that is, in all areas of the
building that must be protected according to the standard),
and it does not accept any partial system, such
as one installed in only one dwelling unit or only in the
basement level of both units.

Exception 2 addresses separation in the area of the
attic of two-family dwellings or duplexes. As long as
the attic draft stop is present and meets the requirements
in Section R302.12.1, there is a provision for the
1-hour fire separation to stop at a ceiling constructed
of 5/8-inch (15.9 mm) Type X gypsum board. Many times
the type of truss or attic rafter and rafter tie/collar tie
configuration will prohibit continuing construction of the
1-hour separation wall all the way up to the roof

duplex firewall.jpg

R302.12.1 Materials. Draftstopping materials shall not be less
than 1/2-inch (12.7 mm) gypsum board, 3/8-inch (9.5 mm)wood
structural panels or other approved materials adequately supported.
Draftstopping shall be installed parallel to the floor framing
members unless otherwise approved by the building
official. The integrity of the draftstops shall be maintained."

*I could be wrong, but I read the above to say that if the CEILING of each unit is 5/8" sheetrock, then a full draft stop between the units of 1/2" sheetrock is all that is required in the attic of a duplex (townhouse is different). My interpretation is that each unit should have 1/2" sheetrock above the ceiling to the roof sheathing, sealed at the joints. Not sure how you can confirm all that during a home inspection. I simply look for sheetrock sealed at the joints and don’t try to confirm the number of layers or thickness.

P.S. The definition of a ‘firewall’ is: “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.”


To answer your first question. Yes. Drywall joints shall be taped or sealed.

The second question. Always best to check with the AHJ.

In my area a duplex is a 2 family dwelling. They are to be separated by firewall, separate entrances etc. It is also classified as R-3 construction, which means an attic firewall has a fire-resistance rating of 2 hours, must have not less than one layer of
5/8" Type X gypsum or 2 layers of 1/2" gypsum wallboard on both sides of dwelling spaces.
In my area a firewall is designed to resist the passage of fire for a period of time not less than the required fire resistant rating of the wall, floor or roof in or between which it is installed.

This is a California Code

R-3 Residential occupancies where the occupants are primarily permanent in nature and not classified as Group R-1, R-2, R-2.1, R-3.1, R-4 or I, including:

Buildings that do not contain more than two dwelling units.

Adult care facilities that provide accommodations for six or fewer clients of any age for less than 24 hours. Licensing categories that may use this classification include, but are not limited to: Adult Day Programs.

Child care facilities that provide accommodations for six or fewer clients of any age for less than 24 hours. Licensing categories that may use this classification include, but are not limited to:

Day-Care Center for Mildly Ill Children,
Infant Care Center and School Age Child Day-Care Center.

Family Day-Care Homes that provide accommodations for 14 or fewer children, in the provider’s own home for less than 24-hours.

Congregate living facilities or congregate residences with 16 or fewer persons.

Adult care and child care facilities that are within a single-family home are permitted to comply with the California Residential Code.

To achieve a 2 hour rating, you need two layers of type X on both sides. Not just one.

U301 wall stud assembly.