Residents of Stoughton and Hollis Halls' top floors returned to their dorm rooms yesterday, after two days of emergency renovations repaired the dorms' ceilings.

A ceiling collapsed in Stoughton Hall on Tuesday, injuring three students.

Fourth floor residents were moved into temporary housing in Loker Commons while engineers investigated the incident. Students on the first three floors of the buildings were allowed to return to their rooms Tuesday night.

Engineers worked late into the night Tuesday and throughout the day yesterday inspecting the buildings.

On Wednesday, an outside engineering firm hired by the University presented officials with a letter that reiterated that the first through fourth floors were safe for occupation, but said the fourth floors of both buildings needed "supplemental repairs."

The firm blamed the collapse on faulty nails that had been weakened by additional layers of the ceiling added over the years.

To stabilize the structure, engineers installed large bolts into the ceilings of fourth floor rooms. In some rooms the bolts were spaced across the entire ceiling eight inches apart.

Rooms on the first, second and third floors had additional supports added in 1992 during building renovations.