The plywood, wedged between all the windows and the home's burglar bars, turned the home into a hermetic box that trapped the fire's heat and smoke and, ultimately, its occupants, fire officials said.
A possible cause of the fire, officials and neighbors said, were the candles the family was using for light because their power had been cut off for nonpayment by the utility that serves the city of Homestead.
There was only one merciful aspect to the fire, though it only augments its tragic dimensions: The children's mother, Claudene Shannon, 34, was not home because she had just given birth to a baby girl hours before.
When she learned of the fire, Shannon left Homestead Hospital before dawn Thursday and, disconsolate, turned up at the fire-charred home, said Josephine Jones, a relative.
''She was sitting in a wheelchair and crying, hysterical,'' Jones said.
The dead were identified as Keeon Shannon, 26, the stepfather; and the four children, Johnny Taylor, 15, Jonathon Taylor, 14, Ashley Taylor, 13, and Sharania Taylor, 12.
The girl born Wednesday was Keeon and Claudene's first child together, relatives said.
Authorities believe the victims died from smoke inhalation, likely within minutes of the fire's breaking out in the living room. All five were found huddled in one of the home's two bedrooms, fire officials said.
Their escape might also have been impeded by locked wrought-iron gates at the front and back doors of the apartment, though investigators believe the fire intensified so rapidly they had little time to get away.
''In this case, the family was cut off,'' said Miami-Dade Fire Lt. Eugene Germain Jr. ``The fire started in the living room. They were cut off by the fire and had to pretty much just stay where they were and succumbed to the smoke.''
This was the second multiple-death house fire in Miami-Dade this year. In February, four siblings were killed in an arson fire that spread through their Hialeah home. Their mother, Marie Auguste, who died of burns she suffered in the fire, set the blaze, Hialeah police said.
Fire officials said they believe a number of mistakes contributed to the family tragedy.
Even without the plywood covering the windows, escape from the duplex may not have been easy.
All the windows had burglar bars. Though the bars were installed without permits, according to city records, every room had at least one window equipped with an escape hatch with quick-release emergency latches, as required by law.
NO WAY OUT
But the two windows in the bedroom where the fire's victims were found provided no egress. The bars on the front window had no escape hatch. The side window did have a hatch, but it was rendered unusable. The hatch, which swings open on hinges, had been pinned shut with plastic ties to allow installation of an air-conditioning unit in the window.
The home also lacked a smoke alarm, which is not required but can provide early warning of fire.
But it was the plywood wedged between the windows and the burglar bars that likely doomed the family, trapping deadly toxins and heat, fire officials said.
They called it a ''very tragic example'' of the importance of removing shutters or plywood once a storm threat has passed.
''It appears these people were boxed in by their own security efforts, and it may have cost them their lives,'' said Miami-Dade Fire Lt. Eric Baum. ``This is a tragedy. Five people lost their lives, but it illustrates how simple things can and should be done to prevent it.''
According to property records, the owner of the duplex is Thomas E. Still, 67. He could not be reached for comment.
Neighbors said the family had been living at the duplex, 449 NW Fourth Ave., for about a year. All four children in the fire were from Claudene Shannon's previous marriage to Johnny C. Taylor, who is serving time in prison on a sex charge conviction.
Ashley and Sharania were seventh-graders at Homestead Middle School, said Principal Vanessa Strickland. Jonathon was at J.R.E. Lee Opportunity School, an alternative school in South Miami.
The oldest, Johnny, was scheduled to attend Homestead Senior High this year but never showed up, said Miami-Dade school district spokesman John Schuster. Johnny, who was recently injured in a fall, walked with crutches.
Neighbors said the family appeared to be struggling financially.
POWER CUT OFF
The Shannons' electricity was shut off Wednesday afternoon because they wrote a check on a closed bank account, said city spokeswoman Lillian Delgado.
The family opened the account in February, but began missing payments in May, Delgado said. ''Someone made a partial payment and the power was supposed to be reconnected Thursday morning,'' Delgado said.
Neighbors who share the duplex said they heard the popping of glass -- apparently the windows breaking from the fire's heat -- around 1:30 a.m.
Opening his front door, William Hanna saw flames shooting out of the apartment next door. He said he ``heard no sound, scream or hollering.''
''They were huge red flames,'' said Hana, whose adjoining duplex is now condemned.
His daughter, Loretta Hanna, called 911.
By 1:43 a.m., Miami-Dade firefighters had arrived.
They used a power saw to pry open the wrought-iron gate at the entrance and started pulling out victims, one by one.
''They were in their night clothes and boxer shorts,'' Loretta Hanna said of the victims.
One of the Taylor girls, Ashley, was airlifted to Jackson Memorial Hospital but died on the way there.
`MY GOD, FIVE PEOPLE'
Hours later in the daylight, William Hanna was overwhelmed by emotion.
''Five people died; my God, five people,'' he said.
Mildred Jones, the children's paternal grandmother, said she went to Homestead Hospital in the middle of the night to tell Claudene Shannon what had happened.
''She could tell by the look in my face that something was wrong,'' Jones said.
' `Did something happen to my kids?' Claudene asked. I said, 'I think four of them are dead.' She went hysterical.''
At daybreak, Jones made a trip to a prison in Florida City to give the news to her son.
''He could barely stand the news,'' she said.
On Thursday afternoon, Claudene Shannon returned to the burned-out husk where her children died.
Weeping, she walked though the duplex and tried to salvage some of her childrens' belongings. She declined to speak to reporters.
'She took some of her daughters' clothing and her son's bike,'' said neighbor Mirian Bonilla. ``I guess she wants them as mementos.''
Some who knew the victims came by to pay their respects. They left flowers and stuffed toys by the door.
The Red Cross plans to pay for the funerals.
The charity also plans to give Shannon food for her and her baby daughter, as well as help finding a new home.
The duplex has been condemned.
''Ninety percent of the time, the victims call us for help, but today, we saw it on the news and went directly to the house,'' said Elda Sanchez, manager of the Red Cross' South Dade branch.
``Who can call us? Everybody died. It's terrible.''