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RE: Concrete Strength Requirements for Residential Projects in SDC D or Higher

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A very quick review of the IRC 2003, Table R402.2 provides a minimum compressive strength.  If the wall is not exposed to the weather, the strength is 2,500 psi.  If it is exposed to the weather then depending on weathering potential the strength varies as follows:

Negligible          2,500 psi

Moderate           3,000 psi and air-entrained

Severe              3,000 psi and air-entrained


To determine weathering potential you need to go to Figure R301.2(3).  In the state of Washington, along the coast is moderate and as you go inland it is severe.


There is also ACI 332, Guide to Residential Cast-in-Place Concrete Construction.  It has something similar but shows the whole state of Washington as severe.


Could not find anything on requirements for special inspections.  Ran out of time.


Gary W. Loomis, P.E., Senior Structural Engineering

Master Engineers and Designers, Inc.

-----Original Message-----
From: Andre Sidler [mailto:asidler(--nospam--at)]
: Friday, January 04, 2008 12:01 PM
Subject: Concrete Strength Requirements for Residential Projects in SDC D or Higher


Fellow Engineers -
Say one was designing a residential project in SDC D or higher with a daylight basement using concrete walls.  The residence above would be wood framed.  ASCE 7-05 says that the concrete walls have to be Special Reinforced Concrete Shear Walls because of the SDC D or higher.  ACI 318-05 Section says that you must use a minimum of f'c = 3,000 psi. Typically one would call out f'c = 2,500 psi for residential concrete so that you don't trigger special inspection, that is until I came across this.  Do either of you know of an exception to this for residential design? Perhaps in the IRC? I don't know the IRC too well.
Andre J. Sidler, S.E.
Quantum Consulting Engineers
Seattle, WA