Go to city hall and apply for a permit. Call or go online first to check requirements, There are probably plans you will have to submit when you file.
First, you may want to check with your local Planning Department to make sure making such a modification is an allowable use within your neighborhood - it probably is. Otherwise, go to your local building department and let them know what you plan on doing to renovate. They will walk you through what permits you need. Generally speaking, if you are doing anything involving plumbing and electrical you'll need to hire a professional who is licensed to that type of work if you are not a licensed plumber or electrician yourself. Depending on how extensive your modifications are, you'll be required to have a building inspector come out and make sure all of your renovations are up to code. You might find this whole process a hassle, but in the end, it will be important to have everything approved and code-compliant in the event you sell your property one day.
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