South Fayette School District could end up with another building on its Old Oakdale Road campus, depending on how school officials decide to deal with a growing population of elementary pupils.

The primary school houses more pupils than any other in Allegheny County -- about 893 pupils in kindergarten through fourth grade. As the township continues to attract more residents over the next decade, enrollment is expected to rise 20 percent, to 1,072 students.

School board members are weighing the benefits of adding on to the building versus constructing a new school. One way or another, the district must make room for more kids.

This year, five portable classrooms adjacent to the building have accommodated an overflow of kids. But William Newcomer, the board president, said adding trailers is not a long-term solution to enrollment growth.

"We're in a bind, so we have to decide on something," Mr. Newcomer said. "But there's a lot of things we have to look at yet before we can actually make a decision."

School board members are considering two options.

After completing a facilities study, Eckles Architecture & Engineering, of New Castle, recently recommended constructing a new intermediate school for grades three to five, and renovating the primary school for grades K-2.

If the fifth grade can be moved into a new intermediate school, there would be more space for grades six through eight in the middle school, where enrollment is expected to increase by 55 percent by 2017.

The second option is to renovate and expand the elementary school. In this scenario, many pupils might have to be moved temporarily into trailers or relocated to other areas in the building during the work.

The recommended plan -- constructing a new building and remodeling the current one -- would cost an estimated $47 million, versus about $37 million for only renovations and additions.

Despite the higher price tag, Mr. Newcomer said the recommended option appeared to be the best choice overall, much to the board's surprise. One reason was that renovations to the 35-year-old building would have to be extensive and more costly than originally thought.

But school directors won't make any decisions until they get more information. In April, the board authorized Eckles to complete a second study to determine the long-term costs of operating an additional building versus running a single, larger one. These costs would include maintenance, utilities, staff, and other non-construction expenses.

After the study is finished in June, school directors will use the new information to help determine a course of action. Mr. Newcomer hoped to decide by the fall.

"It is a major decision and has a major financial impact on the community," Mr. Newcomer said. "And we are caught between trying to get enough information to make the right decision, without prolonging the decision and putting us into a deeper crisis of that building being overpopulated."

Depending on when the district begins the project and how it finances the work, any new space would be ready for occupancy in about two to four years.

Starting work sooner may require a referendum to either borrow money or increase the property tax rate above the normal limit.

If the district instead waits for its borrowing power to increase -- due to paying off older bonds and restructuring existing debt -- a referendum would not be necessary but the overcrowding issue could worsen.

Even now, the elementary school is running out of space in shared areas such as the gym, rest rooms and cafeteria. Next school year, some classes will shift around and some special courses, such as art and music, may travel from room-to-room on a cart because of a lack of space. After next year, though, trailers would have to be added at a rate of two per year.

According to a demographic study completed in November 2007 by Shelby Stewman, a Carnegie Mellon University professor and principal of Stewman Demographics, 179 more students will enter the elementary school by the year 2017. The findings are based on data regarding birth rates, housing developments, migration into the township and other factors.

The Eckles study, completed in March, found the elementary school was too small and in the worst overall condition of all the district's buildings. In addition to there being maintenance issues and too few classrooms, the study found the art and music rooms, library and kitchen are outdated and undersized, and the administrative, guidance and health suites are too small and poorly configured.

"As enrollment continues to grow, these shortcomings will become even more significant," the study report said.