A three-alarm fire early Tuesday caused severe damage to the auditorium at the Burien Annex, SW 146th Street, and 4th Avenue SW. Investigators from the King County Sheriff’s Office have determined that the fire was intentionally set.

According to investigators, the fire was set in or adjacent to an outside porta-potty next to the auditorium at the southeast corner of facility. The fire spread to the auditorium wall and roof and was reported to the Fire Department at 6:25 am. Some 75 fire personnel from five area fire departments fought the blaze, having to cut into the double-layered roof structure to extinguish the flames. The building was unoccupied at the time of the fire and no one was injured. Damage was estimated at $150,000-plus.

A reward of up to $10,000 is being offered for information leading to the arrest and conviction of person(s) involved. Anyone with information can call 1-800-55-ARSON. Arson investigators are currently examining evidence and will be reviewing footage from outside surveillance cameras.

The Burien Annex is a former elementary school that served as the Burien Community Center, housing the City’s Parks Department until it moved in 2010 to its current location at the former King County Library at 14700 6th Ave SW. The City leases currently leases space at the Annex to several non-profit agencies.

Most severely affected are local theater groups that stage their productions in the Annex auditorium and store costumes and props in adjacent rooms. The Burien Actors Theater is currently staging its holiday production, “Coney Island Christmas,” which was scheduled to run through Dec. 22. The youth theater group Hi-Liners also stages its productions at the Annex.

Other agencies housed at the Annex include Para los Ninos, Burien Cooperative Preschool, Meals on Wheels, and Transform Burien, which operates a clothing bank and community kitchen that provides free meals to people in need on Wednesdays and Sundays. Although power to all Annex buildings was cut as a safety precaution, it was restored later in the day Tuesday after the electrical system was thoroughly inspected. Agencies were expected to operate as normal beginning Wednesday.

A separate incident Sunday caused some water damage in the Para los Ninos offices at the Annex. Water was seen leaking from a ceiling by volunteers from Transform Burien who reported it to City maintenance workers. A broken water line was found and repaired, preventing more serious flooding.