First you can go to the township and ask them to update their records. You can also have a Realtor do a Comparative Market Analysis to challange the appraisal. However, keep in mind that because the addition cost you 180,000 does not mean that your home is now worth 180,000 more. Also,a bedroom should not have a walk out to the yard to be considered a bedroom. I hope this helps you. Good luck.
Coldwell Banker Flanagan Realty