The addition ties against the house but also against a patio slab that was never brought up to city code.
This is a great question, Horton Construction. I really like questions like these because they help everyone in the thread, and in the community, how to approach this unique situation. It is almost like a case-study. But, unfortunately, the exact answer is with the Building Inspector and Architect and Engineer on the job. Because, in order to answer the question, you would need to know the condition of the soil, the frost-line for the region, etc.
But, for everyone in the thread that may not know about slabs, I will quickly explain the two main types, which are monolithic and standard. Monolithic is a single-pour, single-unit slab that is deeper at the edges for footings and thinner; i.e. 12", at the floor. A standard, or supported, slab is built with independent units. For instance, the footings, walls and floors are poured independently of each other.
As far as the question is concerned, I would like to hear from foundation experts or concrete tradesmen in the community and their opinion. Also, what did the Building Inspector say? I am interested to hear the responses. But, great question!