Will my ADU be grandfathered?

[Mark Vesu]

Hi all, I recently bought a house that has two units. One main and one junior unit - roughly 450 sq ft. The house was built in 1920's and junior unit was built in the 40's and they built it on the property line, i.e. fence-house-fence that means there is no clearance between the ADU and the fence. The ADU was built before the city was incorporated. What should i do? Will they grandfather my unit? The roof is so bad I need a new one as well. Appreciate your help.