The cause of a house fire that killed three children last week remains uncertain Friday.
Fire officials say they have yet to get inside the home to properly investigate the blaze because of extensive damage.
"Our primary concern with the structure is if you look at the building, it has quite a bit of fire damage," Sioux Falls Fire Marshal Dean Lanier said.
Lanier adds crews haven't stepped foot inside the home since the bodies of six-year-old Alivia and 12-year-old Savannah Coon and their brother, 16-year-old Michael Hensley, were found inside Saturday morning.
"We've got real concerns about the floor holding up at all," Lanier said.
Covering the bowed walls and charred windows, fire rescue nailed plywood preventing anyone from contaminating the scene.
"We also have a lot of concerns about the roof," Lanier said. "The roof has quite a bit of damage. We're concerned about the roof just coming down."
Fire Rescue and insurance agents are working with a local contractor to structurally reinforce the building.
Once that is complete, investigators will be able to safely determine the cause.
Lanier wouldn't say if the home had working smoke detectors at the time, but says the construction attributed to how quickly it burned.
The home itself is more than 100 years old. It was built in 1900 and Lanier says the old construction helped fuel the fire.
"That's why you see so much extension of the fire into the roof space because all that space is basically open. Once it gets into the walls it runs all the way up to the roof," Lanier said.
Lanier says investigators haven't been sitting on their heels over the past week. They've been talking with family and witnesses, and taking pictures of all angles outside and above the charred rental property to aid in the investigation.
He expects to know early next week when the home will be reinforced.