I'm guessing that the footing is overdesigned and can be reduced by the four or five inches required. But you're going to need to do the calculation of the eccentric wall dead plus live loads on the footing and make sure it pencils out. It's a pain, but quite satisfying.

or move the new building by 5"

Thank you for your response but your responses completely misunderstood the question. I'll repost the question again:

I need help to resolve an EXISTING Construction site issue:
A.. Upon soil excavation for a new 2 stories high residential building, we found out that an ADJACENT EXISTING 1 STOREY WITH CELLAR BRICK BLDG HAS THE FOOTING (T Shaped)4" OVER THE PROPERTY LINE INTO MY SITE.

B.. My proposed New 2-Storey Building with Cellar has an 'L" Shaped Footing which is supposed to be installed at the LOT LINE. My Cellar Level is 12 INCHES LOWER than the Cellar of the adjacent existing building.

C.. I would appreciate a recommendation on how to resolve the DETAIL FOR THE NEW BLDG FOOTING AND FOUNDATION WALL. PS, I CANNOT MOVE THE NEW BLDG FOOTING AT ALL. IT MUST BE BUILT AT THE LOT LINE (0' Lot Line)

Jed is right.
Calculate the effect of the eccentricity.
It is a lot of work but unless your design is very thin it should work out.
And I presume that the owner of your site is going after the neighbor for all additional costs.

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P.E. Metallurgy, consulting work welcomed

ookey - are you the design engineer? Site/construction engineer? What's your roll and decision making ability?

These are the options as I see them:

1) Move your footing and foundation wall over and cantilever the wall above to hit the lot line. You'll lose a bit of basement square footage but you'll keep the building above the original dimensions.
2) The developer of your building convinces the owner of that building that's okay to do an analysis of his building to see if it's okay to cut 5" off of the existing footing so you can build yours up to the lot line. Good luck.
3) Come up with some weird combined footing that picks up the 5" of their footing overhanging the property line. I've never been a position to do a 0 setback foundation so I don't know if that's common...but on its face it seems like a horrible idea and I wouldn't recommend it.

Attached, is what I'm proposing regarding the field condition with the existing and proposed footing and foundation. Anu comments?

If that sketch is accurate, I don't like it at all. I'd either get his permission to add to his footing or tell him you're going to get a lawyer and trim his footing and seek damages for trespassing.

You mentioned that the proposed basement level (slab?) is lower than the existing basement level (slab?). That is not so important. Rather, what is the difference in levels of the existing and proposed footing subgrades? The first thing I would do is talk to the adjacent owner and ask if you can trim off the 4 inch projection beyond the property line. If OK and if the new footing is not deeper than the existing, then go ahead. If the new footing is deeper than the old, that is a different problem. You may need to underpin the existing building.

Assuming the new footing is deeper and assuming reasonably average soils, no rock, and no ground water problem; underpin the existing building (with permission). Keep the front face of the underpinning even with the property line. Rear face of the underpinning should be even with the rear edge of the existing footing. Extend the underpinning straight down to at least 6 inches deeper than bottom of the proposed footing and then continue the underpinning for an additional 4 to 6 inches of depth while belling out the front face of the underpinning 4 inches beyond the property line to provide bottom bearing for the underpinning that is equal to the original footing. Trim off the front 4 inches of the existing footing that extends across the property line AFTER the underpinning is finished. Make sure the new footing is founded on well-compacted soil above the belled portion of the underpinning. No reinforcing steel is needed for the underpinning. Dry pack an approximate 2.5 to 3 inch gap between the existing footing and the top of the underpinning. If none of this makes any sense to you, call a contractor who is experienced in underpinning or call me with questions.

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Thank you guys for your contributions to my post. Pham ENG (Structural), your #1 recommendation was what I was thinking after I received the Step Footing sketch, which I believe would work if the situation was a boulder, instead of footing of an adjacent existing bldg.

I'll move my footing and Foundation wall 1 foot from the Lot Line and cantilever 5" back on the first floor to meet the Lot Line. I would provide reinforced conc. piers or columns at min 6' OC and brace/tie with 4' steel beam to the columns (enough to withstand/pick up the conc. blocks wall weight and the bending moment).

ookey, so, are the bottoms of the existing and proposed wall footings at the same elevation?

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