I have a 1916 colonial style home in New Jersey. I’m getting ready to begin an addition and renovation project. One corner of the house will be getting added on to, necessitating a foundation that extends approximately 4-6 feet from the existing house/foundation. The existing foundation is a basement and the foundation walls are of a rather unique construction: two brick wythes with an air space between them with a parge coat on both the ‘dirt’ and interior sides.

The current plan as drawn is for this additional foundation to be a CMU crawl space. There are a couple details related to this that I could use a second (or third, etc.) opinion on.

1. The new crawl space footing is supposed to be at equal depth to the existing basement footing where the two meet, but can then step to a normal crawl space footing depth.

I understand both the code and practical considerations behind this; namely that the new footing should sit on undisturbed soil or engineered fill. Is there precedent/argument for saying that 100 year old back fill is sufficiently undisturbed and that the footing could sit at a more normal crawl space depth even where adjacent to the existing foundation? If the soil tested to the appropriate bearing capacity at normal crawl space depth, is it safe to put the footing there, or are there other considerations to keep in mind?

2. The new foundation is to be tied into the existing with epoxied dowels.

Again, this makes sense in principle, but I’m always wary of drilling into 100 year old brick (two wythes, nonetheless).

The situation I’m trying to avoid is while trying to complete these details, we end up complicating/compromising a perfectly working, albeit old and non-traditional foundation.