As investigators work to uncover the cause of last week’s deadly construction fire in SouthPark, new details are emerging about the type of construction used at the site.

The 239-unit luxury apartment building had a wood-frame construction, according to the developer and county records, an increasingly common style over the past decade.

Known as pedestal or podium construction, the bottom story is made of noncombustible material like concrete or steel. Upper floors are built with wood.

That style is used in building many apartment towers across the country — and Charlotte — fire engineering and construction experts told The Charlotte Observer.

The SouthPark building was under construction when the five-alarm fire broke out May 18. Two construction workers died and 15 others had to be rescued.

There are roughly a dozen other apartment projects like the SouthPark building currently under construction in Mecklenburg County, according to a county spokeswoman.

While international building codes adopted by North Carolina allow for wood-frame buildings, some fire science experts worry about the style’s prevalence.

“The overall size, including height and square footage, matters when a building catches on fire, in this case with enormous amounts of wood,” said Glenn Corbett, an associate professor of fire science at John Jay College of Criminal Justice in New York. He was referring to large wood-frame buildings, like the one in SouthPark.

The more wood on a project, the harder it is for firefighters to put flames out because the framing contributes to the fire, Corbett said. The situation is made worse when the building is under construction because the structure essentially creates a wind tunnel.

Other experts expressed confidence in the safety of wood-frame buildings when complete, saying wood is not the enemy.

They pointed, though, to the need for more early-warning notification systems to workers and first responders when fires start in buildings that are under construction. That’s when buildings are most vulnerable to fire, they said.

Use of wood in construction remains on the rise

The size of the fire like the one in SouthPark would have been dramatically smaller if the building was made of concrete and steel, Corbett said. Those materials can be damaged in a fire, Corbett said, but don’t contribute to the fire.

Wood is credited for its sustainability as a renewable construction material. It’s also cheaper to build with compared to concrete and steel.

What’s more, a greater share of today’s lean labor force is able to frame a building with wood compared to bricklayers and welders, said Mark Matheny, vice chairman of the N.C. Building Code Council. The board is appointed by the governor.

Wood has been one of the most prevalent building materials in the world for over the past decade, said Ray O’Brocki, fire services manager at the American Wood Council trade group.

Construction site fires are often preventable if builders and others follow safety codes, O’Brocki said. He called many construction fires he’s studied over the years predictable and preventable.

“Once the (wood-frame) building is complete and the gypsum wall (drywall) is in, the sprinklers are in, that building is as fire safe as any building made of concrete or steel,” O’Brocki said.

Charlotte fire officials familiar with wood-frame construction

Charlotte fire officials are well aware of the trend of wood-frame construction in apartment buildings. They’ve done trainings on these types of buildings, Peter Skeris, deputy chief of personnel administration, told reporters Thursday.

But once a fire gets going in an open, unfinished building like the SouthPark project, there’s little that can stop it.

Fire Department officials said the fire was accidental and started in a spray-foam insulation trailer at the construction site.

Skeris described the SouthPark site as having two bottom floors with concrete steps, then open scaffolding steps to the sixth floor with “nothing to stop the smoke and fire from traveling up the stairwells.”

Once the wood starts to burn while the building is under construction, a collapse is imminent, Skeris said.

What the building code says about combustible material

Florida-based developer Mill Creek Residential broke ground on its 239-unit apartment building last January in SouthPark, not far from the SouthPark mall.

The apartments were planned to be spread across two buildings, each seven stories high, according to publicly available permits. It’s not clear how many stories were planned as wood versus podium.

Mill Creek Residential declined an interview request this week from The Charlotte Observer. It’s unclear how far along the project was or whether the developer will rebuild on the site.

The permit also revealed more information about the construction type. It’s labeled as “noncombustible walls/protected.” Noncombustible materials typically mean steel or concrete.

In the SouthPark project, builders were using a fire retardant treated wood, according to Mecklenburg County spokeswoman Pamela Escobar. Such wood can be used in place of those noncombustible materials in exterior walls, according to Escobar and a review of state and international building codes.

The international building code, which is typically adopted by states and amended from there, changed in the past decade or so to allow for that exemption, Corbett said.

The North Carolina building code is designed to make buildings safe to inhabit once the building is complete, according to Mecklenburg County’s Code Enforcement division.

The required elements of the code work together to create a safe environment, the division said in an email to the Observer. A certificate is needed before people can live or work in the buildings once “total code compliance” is reached.

Structures are highly vulnerable while under construction. A fire can more easily spread when there are no walls, ceilings or other building components in place, fire science and engineering experts told the Observer.

Worries about wood in apartment buildings

Corbett has been pushing back on building codes and the wood industry for years, as he’s watched more wood allowed to be used in different types of construction.

A 2009 change in the national building code, adopted by North Carolina, increased the number of wood-frame stories that can be built on a pedestal or slab from four to five, the Raleigh News & Observer reported in 2017. The reporting came in the aftermath of a fire that started at a wood-frame apartment building under construction. Nobody was killed or injured in that fire.

Five stories of wood on top of a pedestal is still in the code today, said Matheny of the N.C. Building Code Council. Fire retardant treated wood is designed to behave similarly to a noncombustible material, with the important caveat that the building has to be completed, Matheny said.

But more wood makes it harder to fight fires, Corbett said, and increases the risk of fire spreading to nearby properties. Wood-frame buildings under construction pose a greater risk to firefighters because there is so much surface area for the fire to spread quickly, he said.

A building under construction simply doesn’t have any other fire protections in place like dry wall, exterior coating or walls that can trap and slow down a spreading fire. “It’s a giant wood pallet,” Corbett told the Observer.

Historically, most older wooden apartment buildings were detached from one another, which could slow down fire spread, Corbett said. Today, wood is allowed in most large, attached apartment buildings.

“If this had been a steel-frame building you wouldn’t be calling me about this right now,” Corbett said.

Ways to improve construction scene safety

Building and fire codes have embraced the wood-frame, podium-style construction as safe for the end user, said John Heinen, a Charlotte-based regional practice leader at Telgian. The Arizona-based company is a fire protection engineering consultant firm.

He also emphasized that living in these buildings is safe.

Problems arise during the construction phase, he said, because a large lumber shell lacks fire alarm or sprinkler systems at the start.

Fire experts will point to the importance of compartmentalization — meaning a fire will have a harder time traveling in a building when there are ceilings, walls and other objects inside finished apartments, Heinen said.

Without those touches in place, the building effectively becomes a large wind tunnel.

There also are ways to better warn construction workers on a job site as well as alert the surrounding fire department quickly, Heinen believes. Workers use two-way radios but not everyone has one, Heinen said.

He suggested creating an emergency alert system on every worker’s cell phone similar to an Amber Alert.

Another critical component to consider: enhancing staircases during construction of the building. Building codes don’t always mention encapsulating staircases with a fire-rated material as a means to get off the site in the event of a fire, Heinen said.

Buildings like this are safe for the end user, Heinen said, with inspections across the building for electrical and plumbing and everything in between.

The same can’t be said for the time the building is being worked on. “We need to make buildings safer for workers while in construction,” Heinen said.

Data reporter Gavin Off contributed to this report.

SouthPark Fire

17 months after deadly SouthPark blaze, Charlotte Fire reveals plan to prevent another

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