The law prevents people from claiming the Principal Residence Exemption if they rent out half or more of their space.
But under this week’s ruling, sharing common areas doesn’t count.
Attorney Jon VanderPloeg said the court’s decision sets binding precedent.
"They believed that this situation needed to be clearly stated in Michigan law and they agreed with us that that should be the law," said VanderPloeg.
The court’s opinion seems to contradict current state guidance on handling the exemption.
The State Tax Commission declined to comment.