Are you saying you built the shed portion first so your tax burden is based on that then added the living space later?
It works that way here also. The tax assessor comes out and looks at the initial exiating structure. The tax assessor here does not come back for remodels unless work is done outside the initial walls (without being requested to by the property owner). Check about permitting requirements in you area as you may not even hardly need any. In my area (outside city limits) no permits are required for the structure as long as the property is for private personal use (not for resale within 3 years, business, or renting) and the property owner is supervising the work. These same laws allowed me to be my own contractor building my house and it saved alot of money. I came in at atleast 61K under what my cheapest quote on my house plans was for. I had added tens of thousands in extras in interior changes that was not in the quotes either. I also used that actual cost to get my property taxes lowered. I simply requested a meeting with the Tax assessor and his supervisor about their valued amount after being assessed. I showed them the exact amount it took to build and they lowered my property taxes by 100K of the 120K they where showing above what it took me to build the structure. The only permit that was required I buy while building my house was for the septic tank system.
