We are moving and looking at a house that has a small, shallow play pool. The yard is big enough and the shape is conducive to adding on a deep end to one side.

Is this possible? We built a pool at our current house and I know that the metal in the walls is continuous and overlapping and it's all tied together as one structure. So I kind of doubt it it's possible to add on, but wanted to check with any pool experts on here.

I think you would have rip out the old pool shell and pour a new one for a larger pool. There is rebar, plumbing, etc. that need to be integrated into the shell. You just can't "join" pieces together that way. You would asking for huge structural and leakage problems otherwise.

If it is small and shallow, just dig it out and use the hole as a start for a new one. You may be able to reuse the pump pad and electrical service.

Selective demolition and trying to connect would drive up the cost anyway.

It's not uncommon in the pool remodel world. Not really much different than adding on to a slab. Demo parts/sections and tie in to existing rebar as needed.

Keeping in mind that it's basically going to cost as much as a new pool build. You will be paying minimum charges for Gunite, pebble finish, etc.