Specifications for a single story warehouse foundation call for a PIP wall foundation (no change in footing) to a depth of 4' with #4 rebar lengthwise at 3' OC. The contractor has offered a reduced cost if concrete masonry unit (same thickness) is used. This appears to be OK for this application (building permit approved, I have authority to change). Should rebar be still be installed in CMU joint same as PIP or is no rebar OK? Lots of existing area foundations are without the rebar, but due to 40' span and 4" slab, the PIP was preferred.