Whether it's to ease overcrowding, provide temporary shelter during renovations, or keep class sizes small, many schools around Massachusetts are adding temporary classrooms.
West of Boston, Wayland High School is adding two of the modular, factory-built classrooms that are delivered and installed on site so they can easily be moved and dismantled later. The school, which will use the modular building for science labs, has been growing by about 30 students a year since 2000; 17 science classrooms are double-booked each day, forcing classes to take turns using the equipment.
''We're running out of elbow room," said Gary A. Burton, superintendent of Wayland schools. ''It's like living on a submarine where there's one bed for every three people."
School officials in several suburban Boston districts -- including Stoughton, Avon, and Framingham -- say that modular classrooms are their only solution to stem overcrowding. They say they have been adding modular structures, particularly in recent years, because of a state moratorium on new construction that began in 2003 and lasts until July 2007.
But the head of the new state school building authority, plus teachers' union and health officials, say they worry that the trend may do more harm than good. Kept too long, modular classrooms can grow mold and create unhealthy conditions for schoolchildren, they say.
Katherine Craven -- executive director of the Massachusetts School Building Authority, which oversees school construction -- said modular buildings should be a short-term answer, not the ultimate solution.
''It just doesn't give taxpayers the most bang for their buck," she said. ''We want to make sure the dollars we spend go to the best use."
State education and school construction officials were unable to provide an estimate of how many school districts have such temporary classrooms.
School officials said they began using modular classrooms because they are cheaper than new construction projects, take less time to build, and, in the case of newer models, resemble regular buildings.
''We're sort of held captive," said Ralph Dumas, school business administrator for East Bridgewater, which plans to open modular classrooms at an elementary school next fall. ''It could be 10 years before a new building is opened. It could be longer. This is the best solution we could come up with for the problems we're facing right now."
Modular buildings cost about $100,000 per classroom, depending on features, and can be built and delivered in less than six months, said Cliff Cort, president of Triumph Leasing Corp., a company based in Littleton that leases and sells modular classrooms.
Health officials say problems can occur when schools keep temporary buildings for more than a few years. Without proper care, leaks in the roof can lead to mold growth, triggering asthma attacks, while poor ventilation can cause headaches, nausea, and eye irritations, said Suzanne Condon, director of the Center for Environmental Health at the state Department of Public Health.
Tolle Graham, coordinator of the Massachusetts Healthy Schools Network, has similar concerns. While problems with mold occur in permanent buildings, they can occur more frequently in temporary classrooms, which are designed differently and often not maintained as well as a permanent structure.
''The temporary turned into permanent," Graham said, ''and that's the problem."
At Silver Lake Regional High School in Kingston, officials saw problems when they kept a modular building for seven years, two years longer than they intended. The school added the first one in 1995, when enrollment was about 1,800 students.
Principal Richard Kelley said the wear and tear became visible. The wooden floors weakened, and roof leaks caused the walls to deteriorate in the first modular building. In a second modular building, added in 2000, the air conditioner stopped working one summer, and mold grew in the carpet and in the vents, giving the classrooms a musty smell, Kelley said.
''They did serve us well, but they were showing their age," Kelley said. ''They're not made to last forever."
In school districts with the newer modular classrooms, though, officials say the buildings have been problem-free.
''The teachers are quite satisfied, the parents love it, the community is thrilled. It's a beautiful space," said Margaret Frieswyk, superintendent for Avon, which added a permanent modular building last year.
A state teachers' union official said he's not convinced of the modular classroom's merits.
''If a community needs new schools, they need to be building new schools and not something that looks like a trailer," said Edward Doherty, special assistant to the president of the Massachusetts Federation of Teachers.
Contractors say that newer modular classroom designs make the structures look like part of the main buildings; a walkway connects the modular and main buildings.
''The older perception was trailer or mobile home," said Bill Ryan, the territory manager for M Space Holdings, a New York based company that supplies modular buildings to schools along the East Coast. ''No one wants that."
In Stoughton, the Robert G. O'Donnell Middle School's five-year-old brick-face modular building blends in with the main building so well that many students believe it's merely an additional wing.
To get to the modular classrooms inside, O'Donnell students walk from the main building through a covered hallway on a ramp connected to the modular building. A single hallway divides the six classrooms and three restrooms for boys, girls, and faculty.
Inside, the main building's walls are concrete block; the modular building's walls are drywall with a vinyl covering.
Stoughton installed the modular building because its student enrollment, which had been increasing by 20 to 30 students a year, reached 1,000 five years ago; the school building is meant to hold 900, Harding said.
The modular building was supposed to be temporary.
''Originally, it was planned to move from middle school to high school when the population bubble moved," said Joel Harding, supervisor of support services for the Stoughton school district. ''The bubble never moved."
Students and teachers say they love it, especially since each modular classroom has its own climate control, while the main building has a central control and no air conditioning.
''I don't want them to move me anywhere else," Katia Rigas, a French and Spanish teacher, said as she sat in a bright classroom adorned with pictures of Chile, Argentina, and Peru.
School administrators don't know how long they'll keep the building. ''I hope forever," said principal Wayne Hester. ''We're strapped for rooms right now."
Russell Nichols can be reached at email@example.com.