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The Supplement to the
I-codes has been issued and the IBC has been amended the plate washers to the
same as the IRC, 3x3x1/4 plate washers.
Additionally, when doing residential work, you are allowed to use as
much or as little of the IRC as you want, provided that anything that deviates
from the IRC is done per the IBC. See
IRC section R301.1.3. If it doesn’t
need to be designed, leave it and let it conform to the IRC. If you aren’t comfortable
with that, that is your call.
From: Jordan Truesdell, PE
Sent: Thursday, December 16, 2004
Subject: Re: 3x3x1/4 plate washers
in IRC vs. 2x2x3/16 in IBC
At 06:13 PM 12/15/2004 -0900, you wrote:
I know people have talked about plate washers for wood sill plates a bit on
this list but was hoping someone could spark my memory. Anchorage is currently
going through the 2003 code adoption locally. 2003 International Residential
Code Section R602.11.1 requires 3x3x1/4 plate washers for foundation sill
plates in Seismic Design Category D. 2003 IBC 2308.12.8 requires 2x2x3/16
plate washers for conventional light frame construction in Seismic Design
Category D and IBC 2305.3.10 requires 2x2x3/16 plate washers for engineered
Is there a change to require
3x3x1/4 plate washers in an accumulative supplement or errata to the IBC?
The question from the local homebuilders has been when a one or two family
dwelling is engineered can they use the 2x2x3/16 plate washers in the IBC?
M. Haan P.E.
Deputy Building Official
Mission Statement: Guide safe
construction and responsible development for the community.
Here's my take on this: If you have an engineer design a residence, it no
longer falls under the IRC provisions. The IRC is a prescriptive code. It
SHOULD be far more conservative than a sharpened-pencil design, principally
because there is no review by a licensed professional. If you want to
save the money by not hiring a professional to create a compliant design,
you'll be "stuck" with a very conservative approach (3x3x1/4
washers). If you are willing to spend the money to have the design checked and
verified by a professional who is going to calculate actual loads and trace the
load paths to the foundation soils, then more latitude is offered on the
minimum sizes (2x2x3/16 washers).
This is, in fact, one of my beefs with the IRC - in most cases it's too
non-conservative. Example (my apologies to regular readers): If I design
a reinforced concrete wall, I MUST include 0.2% horizontal reinforcement,
and cannot space bars farther than 18" o/c. If I design a 12"
concrete wall, I must use two curtains of steel. In the IRC, a builder
can "design" a 12" concrete wall with a single curtain of steel,
spacings of up to 72" o/c and NO horizontal steel whatsoever. Not
only that, but the code's allowance of below-grade unreinforced CMU is
appalling. I do a reasonable number of residential surveys, and I have
yet to enter a basement more than 15 years old that doesn't have a crack in the
mortar which would completely eliminate any tension bond in the CMU. Most
unreinforced CMU basements 20+ years old with more than 6' of backfill have at
least one crack that is 1/16" wide and spans more than half the length of
the wall. Another example? Collar ties. IRC allows the use of a non-structural
ridgeboard on a stick framed 3.5 in 12 vault, as long as there is a collar tie
1/3 of the way down from the ridge fastened with 3 - 8d nails each end.
That collar tie isn't going to do squat. You're probably going to need
more capacity than you can get with nails to hold the walls together in that
case. But it's allowable under the IRC.
Sorry for the rant, but it's one of those things that makes me look like the
"bad guy" every time a builder walks into my office. He can build it
"with less" and be code compliant than if I give him an accurate
engineered design. I have no sympathy for having to go get a 1/4" plate