I would like to pour a new footing and foundation wall along side the inner perimeter of an existing clay tile foundation wall. I’m about to rehab an old house (1899) which has a double thickness of tile block for the foundation and outer wall. The two walls run parallel and appear to be independent. The inner wall was built with pockets to support the floor joist. This wall has deteriorated to a point that the floors are no longer level. It appears that the grout has deteriorated beyond repair. All that remains is a dry chalk like fine powder between the clay tiles. Everything should be replaced, so this is why I think it would be best to build two new levels atop new foundation walls. I would like remove the inner foundation wall and pour a new concrete footing / foundation wall adjacent to the existing outer foundation wall. I will be forming one side with plywood 2x4’s and structural bracing as required. My main concern is can I pour a footing and foundation wall against the existing wall thus forming the configuration of an L, or is it best to center the foundation wall on the footing thus forming an inverted T. The T configuration would evenly distribute the loads but would leave a space between the existing wall and the new wall. The L configuration which I’m in favor of would fill the void between the two walls, but would not center the loads. Forming for the walls would be quicker and easier also. Any response, suggestion or another technique would be greatly appreciated.