NARRAGANSETT — The collapse of a deck during a college house party Saturday night was due to overcrowding and “deterioration and rot due to water damage” on the siding to which the deck was attached, Building Official Anthony L. Santilli Jr. has concluded.

At least 21 people were injured at 37 Sakonnet Blvd. when a deck pulled away from the house, broke in the middle and fell.

A minivan and a car parked below broke the fall, the police report says. Injuries ranged from cuts, bruises and ankle sprains to a broken wrist, bloody nose, broken jaw and a possibly broken pelvis, the report says.

The 480-square-foot deck, built in 1988 of pressure-treated wood, met the standards that were in place 20 years ago, Santilli said yesterday. The pressure-treated ledger board, which attaches the deck to the house, was fastened with 16d common nails, which were considered adequate in the 1980s, he said, and a few lag bolts, which have been required on decks built after standards were raised in 2006.

The five-bedroom raised ranch, built in 1977, is between Black Point and Scarborough State Beach, on the opposite side of Ocean Road in a neighborhood of summer rentals that in the fall become student residences. Tax assessment records show the owner as Jean Chui Chun Fong.

The police report lists four residents, all of them 21: Steven D. Forcello, of New York, Eric J. Maley, of Massachusetts, and Christopher E. Roth and Russell A. Detres, both of New York. The four gave written statements to Patrolman Daniel A. Sorice, all of them saying that no more than 15 people were on the deck when it fell. The report lists the 21 victims, mostly URI students and most with Narragansett addresses, as: Jessica L. McCormick, 20; Ashley E. Earner, 20; Elyse H. Gibberman, 20; Kristin M. Frederick, 21; Courtney Bento, 18, of Mountainside, N.J.; Evan Frankel, 21, South Kingstown; Nicole Arpino, 21; Marrisa F. Fisher, 20; Kelly Spence, 20, of Riverhead, N.Y.; Amy M. Loflin, 21, of Barrington; Cristie M. Tomei, 20; Elyse Deo, 21, of Berkeley Heights, N.J.; Tara Graziano, 20, of Berkeley Heights, N.J., Carly T. Benedetto, 20; Alia Fater, 19, of Albertson, N.Y.; Allison S. Togliati, 20; Noah Haroian, 19, of Warwick; Lauren E. Morris, 20; Adam Allen, 27; Dina Bulson, 21, of Milton, N.Y.; and Michael J. Rutledge, 21.

Officer Kyle Hemmerle wrote that when he and other officers responded, at 11:40 p.m. Saturday, to a call about a deck collapsing with 60 people on it, he saw about 40 people on the property, some of them leaving on foot.

He spoke with Sean Kelly and James Pappas, both 21. Pappas, who left the deck just before it fell, said 15 to 18 people were on it.

Kelly, who said he was with about 20 people on the deck, heard it crack. He did not require medical attention.

Two of the injured said that between 40 and 60 people were on the deck when it fell. Fater, 19, said “the deck was so crowded, I could not move,” and Graziano, 20, said “there were so many people, I could not walk.”

Patrolwoman Desiree L. Dugan said she would not recommend issuing a town nuisance sticker because the partygoers were not disorderly, just standing around talking, and officers were called because of the collapse, not because of noise.

dnaylor@projo.com