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Re: Code Compability

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It of course depends on the building authority as well as the character and
size of both the addition and the original construction, but I think the
short answer to your question is no.  You should review 1997 UBC Chapter 34
(Existing Structures), specifically Section 3403.  Unfortunately, that
Chapter is in Volume 1, and many engineers only keep Volume 2 on hand -- you
may need to dig for it.  If you don't have it and you're designing in UBC
country you of course need to get a copy.

Fundamentally and exclusive of any code requirements, the governing
principle should be that which medical doctors often quote, "first, do no
harm."  This is in fact the approach taken by the UBC and most other model
codes.  They permit additions, alterations or repairs to be made without
upgrading the existing construction so long as (a) all NEW work complies
with current requirements, and (b) the modifications do not make the
existing construction less safe than it was when you started.  What this
means is that if your addition will result in an increase in load in any
existing structural component, you are required to upgrade THAT COMPONENT,
but you need not modify portions of the existing structure that are not
materially affected by the modifications.

There are of course exceptions for patently unsafe structures (try to avoid
operation on critically ill patients) and the effects of a major
structurally contiguous addition in earthquake country would typically
ripple a long way through the existing building (so that you would be
required to do what is essentially a full upgrade anyway), but the bottom
line is that it is NOT always the case that an addition requires the
existing construction to be brought up to current code.

Drew A. Norman, S.E.
Drew A. Norman and Associates
Consulting Structural Engineering
Pasadena, California

----- Original Message -----
From: "Ryan Lawton" <RLawton(--nospam--at)>
To: <seaint(--nospam--at)>
Sent: Wednesday, October 10, 2001 5:40 PM
Subject: Code Compability

> Gentlemen
> It has been my experience that when you have an existing building designed
under one code, lets say UBC 94, and you attach a new building to the
existing, years later, that the existing building needs to be brought up to
the code of the new building, hence UBC 97.  Is this always the case? I have
had buildings in the past that had to be separated because the old building
(old code) could not feasiblely be brought up to the new building code.
Depending on which codes, I bet this could be done most of the time, but
when you are talking about UBC 94 to 97 in seismic zone 4, with a lot of
mass, bringing the old up to new cant be done for a penny or two!
> Thanks in Advance
> Ryan

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