The foundation from our first module has rebar projecting in all four directions to accommodate expanding in any direction that we wanted to.

Our next additions will not have rebar projecting in all directions because the design for the total build-out has been determined.

If one was to add on to a side of a foundation without rebar projections, one could use a long masonry bit and a hammer drill to create holes into the existing foundation. Then, rebar can be inserted into the holes and construction adhesive can be used to secure the rebar into place.