Auckland police have arrested a 34-year-old woman over the fire at City Garden Lodge in Parnell.
The blaze on 7 April extensively damaged the boarding house on St Georges Bay Road in central Auckland, with 10 of its guests evacuated.
The building had failed its Building Warrant of Fitness twice last year over several areas of non-compliance, including a problematic external fire escape.
Detective Senior Sergeant Chris Allan said Auckland City Criminal Investigation Branch arrested a 34-year-old woman on Friday afternoon in relation to the fire.
She had been charged with arson and was expected to appear in the Auckland District Court today.
"Police would like to thank the members of the public who assisted with our enquiries and contributed to this result."
Seema Chatly, who owns City Garden Lodge with her husband Suresh, said they were glad to hear an arrest had been made.
"We are very relieved that this happened. We are very happy that ... they've got her."
The future of the building was unclear, and they were still deciding what to do with it, she said.