johnstaci - Foundation Thickness on Brick Home
Most residential building codes, including the IRC, are silent about the reduction in wall thickness behind a brick shelf in a concrete foundation.
The best design resource for such conditions is ACI 332 "Requirements for Residential Concrete Construction and Commentary" which is accepted as an alternate design method by the latest version of the IRC. It is more comprehensive and easier to understand then the IRC. Anyone building residential buildings should own this document.
According to ACI 332, for a full basement foundation wall (with the first floor framing sitting on and bracing the wall), an 8" inch wall may be narrowed to 4" (behind a 4" brick shelf) if a vertical #4 bar is placed on the inside face of the wall at 24" o.c. and extending at least 12" into the full thickness part of the wall. The maximum height of the narrowed wall is 24".