He or she will submit design drawings and calculations of the solution, to the building authority for approval and permit. Upon receiving the permit, when you are ready to begin construction, the contractor can then proceed to build-out the structure per the engineer's or architect's specifications. This is the process in California, based upon the state building standards, Title 24. The process in the other states is very similar.
Of course, if you don't create an addition to the house, and just remove or relocate a wall(s), you then have infringed upon a contiguous space and decreased its size, so you have to weigh which option is the best for you. Is it worth giving up the other space to increase the size of the kitchen? In my experience, if you can do without the adjoining space, it is much better to devote that extra space to the kitchen.
Most clients require something substantially less than all of this, but I bring it up just to emphasize that how you utilize your kitchen has a strong influence on the design and therefore, as I mentioned, you should think about how you want to operate and what you want to accommodate in your kitchen. You can start to think about what type of appliances and features you would like. Think of the three major work areas of a kitchen: Food Prep (refrigerator and sink), Cooking (cook top, oven and microwave) and Cleanup (sink, dishwasher and recycling). You will find a myriad of styles and options available which you and your designer will need to carefully consider. More planning, of course!
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