Each school day, tens of thousands of Utah children make their way into stand-alone classrooms a stone’s throw from the main campus buildings where their peers study.
Commonly known as “portables,” these modular structures occasionally get moved around, or they remain in place for decades as a low-cost alternative to constructing newer and bigger schools to relieve overcrowding.
But what, beyond gravity, secures these buildings to the ground?
That question lacks a clear answer in Utah, with a decentralized network of boards for 132 school districts and 127 charter schools in charge of overseeing structural planning.
And while most of the hundreds of portable school buildings in use in Utah are similar in construction, minimum architectural and engineering requirements that cover them are loosely defined, beyond rules that seismic and soil conditions where they are located be studied.
“They’re not required to be on a permanent foundation,” said Natalie Grange, an assistant state superintendent for the Utah Board of Education. “When they’re installed, they are hooked to the ground in some way that satisfies safety and seismic requirements.”
On Wednesday, leaders of Utah civil and structural engineering groups issued a joint statement urging new, more stringent standards on modular buildings, including portable classrooms and offices.
When these modulars are used for more than 180 days — virtually all portable classrooms in Utah are used beyond that timeline — they should be considered “permanent” structures and subject to more rigorous structural codes, the professional groups said.
“Unanchored and/or unbraced structures intended for occupancy do not meet the provisions of the building code and present a risk to the health and safety of the occupants,” said the statement.
Issued Wednesday, the statement is signed by Anthony Schmid, president of the American Society of Civil Engineers Utah Section; Conrad Guymon, chairman of the Utah Section’s Structural Engineering Institute; and Troy Dye, president of the Structural Engineers Association of Utah.
Matt Roblez, a past president of the the American Society of Civil Engineers Utah Section, said he became concerned about the regulatory ambiguity surrounding construction of portables after inspecting a series of modular units intended for use at Utah schools.
Building codes did not appear to be enforced, Roblez said, but unlike some states, Utah does not have clearly defined requirements or guidance for prefabricated classrooms.
“At the minimum, Utah schools should adhere to the code more strictly by securing portable classrooms to the ground with use of a permanent footing and foundational system,” Roblez said. “Until this code can be properly enforced, Utah should write an adopted standard for schools to follow.”
Supply and demand
Salt Lake County’s five school districts operate a combined 604 portable classrooms, according to district spokespeople. The numbers range from a high of 250 portables in the fast-growing Jordan School District to six portables in the comparably small Murray City School District.
Utah’s two largest school districts, Alpine and Davis, operate 363 and 347 portable classrooms, respectively.
The state’s average student-to-teacher ratio is 21.8, according to the most recent data from the state Board of Education. By that math, portable classrooms in north-Utah County, Davis County and Salt Lake County house roughly 30,000 children.
Davis School District spokesman Chris Williams described the modular units as a necessary evil. School construction often lags behind swings in student population trends, and modular classrooms allow districts to adjust more quickly to those trends.
When the Davis district last sought voter approval for a bond, written materials on the measure noted that if all the district’s portables were stacked vertically, they would form the tallest building on Earth.
“We wish we could get away from them, but as you see from the numbers, 347 of them, we use them quite a bit,” Williams said. “We definitely make sure that it’s safe for people to occupy them.”
For its portables, Davis relies on a typical system of placing the buildings on rails and tying them to bars that extend 2 to 3 feet into the soil beneath. That setup, Williams said, allows portables to absorb wind or seismic activity without sustaining damage.
In case of a major disaster, classrooms anchored in this way might be shaken off their base rails, Williams said, but would likely remain otherwise intact.
“They’re made so that they can kind of sway back and forth,” he said. “If they fall, they’re going to fall a few feet.”
He said Davis School District’s portables are all on top of soil, without a foundation or hard surface beneath them.
“Our portables are placed on the grass or on dirt,” Williams said. “We do not lay a cement pad down or asphalt to go underneath them.”
Roblez said Davis School District’s approach — while typical for districts across the state — fall short of safety standards.
“Ground stakes, the tool that many modular units use for stability, do not meet the provisions of the current code for permanent foundations,” he said. “Per the code for a permanent structure, buildings require a footing and foundational system that is required to withstand gravity loads, wind and seismic events and be placed at frost depth.”
Quick fix for overcrowding
In Granite School District, all portables installed within the past six years have been placed on hard surfaces, spokesman Ben Horsley said.
“It’s more secure, clearly, having it on concrete or asphalt,” Horsley said. “You will find some [on soil], even within Granite District. That’s not to say they’re not safe and secure.”
Like portables in the Davis district, Granite’s classrooms are tied to pairs of stakes that extend into the ground. The district has also moved to using steel frames, instead of wood, over the past decade and bolts the portables’ base siding into the asphalt or concrete beneath them, adding an extra level of anchoring, according to Steve Hogan, the district’s director of planning and boundaries.
Hogan said the district chooses flat areas to place portables — to avoid issues such as rain erosion or shifting soil — and keeps the buildings as low to the ground as possible for accessibility and to lessen the distance a building would drop if it fell off its footings.
Because building codes for portable classrooms are not spelled out in detail, Horsley said the district looks to residential mobile homes as a standard for its modular buildings. He declined to comment on the design and anchoring of other districts’ portables, but noted that he’s unaware of any safety incident in Utah related to the structural integrity of modular buildings.
“We’ve tried to go above and beyond what those [mobile home] requirements are,” Horsley said. “I think we’re about as prepared as we can be and we’ll continue to upgrade. If we see other logical, reasonable ways that we can make these safe, we’re happy to look into that.”
Ross Wentworth, an architect with the Salt Lake City-based firm Naylor Wentworth Lund, has designed portable classrooms for several school districts, most recently Jordan School District.
Wentworth said most districts use a standard design plan for modular buildings, which is then tailored to specific conditions. And because portables are lightweight, detached from and typically newer than other district structures, Wentworth said they’re preferable to other buildings children could find themselves in during an earthquake.
"If I had to choose a place for a son or daughter to be, with respect to seismic activity, it would be in a relocatable,” he said.
Jenefer Youngfield, school construction and safety specialist for the state Board of Education, also referred to residential mobile-home design standards as a guide for the structural requirements of portable classrooms. Like mobile homes, she said, portables do not need be secured to a fixed foundation — unless the designing architect decides that site conditions require it.
Building plans for portable classrooms must approved by a certified examiner, she noted, and public concerns regarding safety can be submitted to the state Board of Education for review.
“The long and short of it,” Youngfield said, “is it’s up to the architect or engineer.”
‘Good, durable facilities’
Wentworth said if there is a regulatory gap in standards for portables, it rests with how they are connected to the ground. Like Williams and Horsley, the school architect speculated that a worst-case scenario could shake these classrooms loose of their footings, causing them to fall 1 or 2 feet to the ground.
But Wentworth emphasized that the structures remain safe when adequate attention goes into their design and installation. And while many spend their useful life at a single location, the buildings are built to be moved, he said, helping administrators respond to shifting enrollment.
“Our experience is that they’ve been pretty good, durable facilities,” Wentworth said. “They certainly solve a unique problem for the number of students we deal with in Utah.”
But Roblez said the lack of clear regulations and minimum standards is only adding to the potential for structural damage.
He urged that more be done to mitigate the risks, with sufficient foundations being the first line of defense against earthquakes and major weather events. Roblez also called for wider public awareness on the issue.
“Parents should ask questions of school facilities managers to understand how schools are adhering to the building code,” he said.
Horsley said Granite School District welcomes feedback from community groups on structural safety, acknowledging that modular classrooms are “the next best option” to a traditional schoolhouse.
“Our preference,” he said, “would obviously be a seismically sound, permanent facility.”