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Oh well, you'll find out if you did a good job or not. However, most Codes or Laws don't require the Property Owner to get a permit for most anything WITHIN an existing building's footprint. Yes, they do strongly suggest it and most every Zoning Department will lie right to your face to get money.
BUT, if you added to the footprint then you, potentially, could be in a real mess...EVEN IF you did a great, wonderful and perfect job. If Zoning gets wind, they could require the addition's removal and still fine you heavily (hundreds or thousands a day) or condemn the entire property.
If you choose to re-build it in that sucks-big-time-case, you'll be getting permits and inspections galore or going to jail with more fines. And maybe you can't go as big, because you exceeded the open-space percentage or setback regulations or are now required to retain water run-off, etc. You'll get every page of the book thrown at you, since you didn't bow to their divinity.