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RE: What's the difference between a fire wall and a party wall

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Clifford, There is a lot of confusion on this topic, let me add more...
Townhouses can be built to either the IBC or the IRC [no matter how many are
lined up (could certainly be 100 for example), as long as they have separate
means of egress, are open on at least two sides, and each dwelling extends
from the foundation to the roof].  The driving force as to which code (IBC
or IRC) to use weighs heavy on what type of common wall you'll use (either a
common 2 hour or two separate one hour walls or a one hour).  

This discussion is for R occupancies only.

IBC:   Multi-family provisions classified as R-2 have fire walls.  Fire
walls have more restrictive requirements than the old area separation walls
in the UBC: 1) Structural independence 705.2, 2) horizontal continuity
705.5, and 3) vertical continuity 705.6. 
1) Fire walls must be design to allow collapse on either side independently.
No structural members may cross the fire wall. Floor framing may not
penetrate the fire wall (platform framing not allowed). 
2) Fire walls must extend the full width of the building and include an
additional 18" beyond the exterior walls.  Exceptions allow the fire wall to
terminate at the exterior wall sheathing.  All exceptions require 3/4 hour
protected openings within 4' of fire wall.  Protected openings are a problem
when you have entrance and garage doors, or windows within 4' of the fire
wall but there are ways around it...add an 18" continuation past the
exterior wall.  Balconies, roof overhangs, and other projections have
specific design requirements too.
3) Fire walls must extend from foundation to a point 30" above the roof, or
use a parapet 705.6 (see exceptions).  All exceptions prohibit roof
penetrations within 4' of fire wall (includes roof vents but I think there
is an exception for foundation vents).  Fire walls cannot have horizontal
offsets.

IRC: Fire walls may be used to convert the R-2 to a R-3 per 705.1 if
constructed as party walls. 503.2 (Stacked townhouses must be designed under
the IBC). Two-hour party walls (can assume a property line) are required
between dwelling units (2) one-hour walls per R302 or a single two-hour wall
per R321.2 may be used to separate dwelling units. Structural independence
not required (R321.2.4 item 5). No horizontal continuity requirement.
Garage separation is limited to a single layer of 5/8 Type X sheetrock on
the garage side. No opening protection is required (e.g. forced air
registers are OK) but no openings are allowed into the garage.  Party walls
may terminate at exterior sheathing.  Vertical continuity is less
restrictive than IBC.

Benefits of IRC include: 
Allows forced air openings between garages and dwelling units.
Technical requirements are more straight-forward.
Two-hour fire wall requirements are less restrictive.

Benefits if IBC include:
In multi-family buildings without garages, one-hour dwelling unit
separations may be used.
In multi-family buildings with garages, one-hour dwelling unit separations
may also be used where there are no openings in the garage ceiling assembly
(no forced air duct penetrations).


-----Original Message-----
From: Clifford Schwinger [mailto:clifford234(--nospam--at)yahoo.com] 
Sent: Thursday, August 21, 2003 6:28 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: What's the difference between a fire wall and a party wall

The more I read the building code (with regards to
party walls and fire walls), the more confused I get.

When you have townhomes (we call them rowhouses in
Philadelphia) there is typically a bearing wall (a
party wall) between adjacent houses. Do current codes
permit a single party wall straddle a lot line and
support load from two adjacent townhouses, or does
each townhouse need its own structurally independent
load bearing party wall from foundation to roof? Is
there a different answer depending on whether the
units are townhouses where the owner owns the land and
structure versus whether the units where the homeowner
owns only the structure versus whether they are
condominium units?  (The proposed shared wall that I
am referring to would be a masonry wall capable of
remaining intact and structurally sound if the
structure on one side of the wall burns down.)

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