I assume the contractor doesn't want to deal with a second series of forming and that's why he want to use "B". I use a detail that makes a curb the width of the wood wall and the depth of the floor slab on the first pour so that when the slab is poured, it will use the curb as the form and still be supported by the rest of the footing below it.
S.Macie, P.E.
SLO, CA
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