Less than 10 years ago, the only Assembly of God church on South Whidbey held Sunday services for about 20 people in a building on Highway 525 too small to be a house.

This Sunday, the South Whidbey Assembly of God will officially open the doors on 30,000 new square feet of space and join the growing ranks of supersized island churches.

At the same time, the Assembly is one of a few island church buildings that play a big role in attracting church members.

The church has put a total of $2.4 million into additions and remodeling since 1996. Though the church’s approximately 750 members have been using the new space as it has been finished, Sunday will be the day to celebrate the almost-finished final product.

Like several other local churches have done in recent years, the Assembly of God has put an emphasis on building space suitable for a number of uses. Assembly pastor Matt Chambers said his congregation wanted a building that can be used by church members and the public all hours of the day every day of the week.

This desire is perhaps best illustrated in the church’s sanctuary. Built like a gymnasium with a stage-like altar, the rubber-floored room serves at least double duty during the week. With arena lighting, retractable basketball hoops, stage lights and video projection screens, it is as much a place for worship as it is a practice facility for the South Whidbey Basketball Association or Little League baseball .

“We didn’t want to build a room that could only be used once a week,” Chambers said.

With a young congregation in which the average age of adult members is in the low to mid 40s, the Assembly is still growing. Classroom space in the attached Langley Christian School is as much for Sunday school and weekday classes as it is for weekday and weekend adult groups. There is also a nursery wing in the expanded building, a commercial kitchen, and offices for almost every member of the church staff.

Also using the new space are week night youth groups, Boy Scouts and anyone else in the community who needs space to meet.

All this makes the church building part of the greater community, Chambers said. At the same time, at least in the experience of another South Whidbey church, bigger, better church buildings help churches bring the greater community in for worship.

The Rev. Jim Lindus, pastor of Freeland’s Trinity Lutheran Church, said many people who have gotten used to being at the church for non-spiritual reasons have become members over the years. Having completed a $1.5 million expansion project last year, Trinity now has a gymnasium and meeting and class rooms.

Lindus said the church’s membership has swelled to over 1,000 people in the six years since Trinity move out of its small building on Highway 525 and into its new building further off the road. It’s not unusual, he said, for a person who has been to the church for a Kiwanis Club or Alcoholics Anonymous meeting to decide to join after getting used to the place.

“That makes a difference for people,” he said.

Trinity is actively promoted as a public space. It is the site of government meetings, voters forums, athletic events and social group meetings. Lindus said this winter promises to be a busy one in the church’s gymnasium, with children and adults in a number of sports using it to get out of the weather.

“Our gym is just in constant use now,” he said.

Even when it is not all packed with people, just having extra space to move around in is a draw for churches. The Rev. Bob Welch, pastor of Langley’s Christian and Missionary Alliance Church, said a number of expansions over the years have not only made the church a place for public events, but one in which members feel comfortable.

With its own small gym space, a stage for performances, classrooms and large sanctuary, the CM&A church has not done much construction in the past decade. But the time may come when the 400 members of the congregation need more space, Welch said. He said he starts thinking about building whenever the sanctuary is 80 percent full on Sunday mornings.

“People don’t like to be crowded,” he said.

With construction just coming to an end back at the Assembly of God, that crowded feeling should be a few years away. Once the hammering stops, however, the church and its congregation will experience a new feeling, since there has been nearly constant work happening in the building since the first part of the building was finished in 1989.

Chambers said he hopes Sunday’s grand opening will attract people from all over the community, whether they are church goers or not. He said his congregation, which has already paid out $1.8 million in cash for its building project, has intended from the beginning to share their church with the South Whidbey community.

As for future construction, Chambers said the church has plans for more additions in the future.