Last year we built a gorgeous in-law suite for my mom. She paid for it from part of the proceeds of her house - cost was around $190K (my dad has been gone 20 years). We just received a reassessment and the new mortgage went up about $500 (property tax + insurance). We are in pricey Fairfax County. In her old house, she was tax-exempt. I presume with the in-law suite this falls on us now? I wasn't sure if there are any rules or laws on in-law suites that have adjusted taxes if the inhabitant was tax exempt prior?