A tearful father described the moment he found his son crushed under a mantelpiece.
An inquest into the death of four-year-old Matthew Green heard the 110lb stone lintel had only been held on by adhesive.
The masonry collapsed at the house in Towcester, Northants, in October 2005, crushing Matthew's heart in his ribcage.
At the first day of the four-day inquest at Rushden & Diamonds Football Club in Irthlingborough, Northants, his parents told the court they had never had any worries about the fireplace at their Persimmon Home, bought in June 2003, until the day of their son's death.
The accident happened as family friends arrived to visit the Greens in Coulthard Close, Towcester, on October 15, 2005.
David Green, 38, said: "I was just greeting our two friends and then there was a very very loud crash."
Mr Green, managing director of his own insurance broker's business, broke down in tears as he described finding his son.
He said: "The whole mantelpiece had come off and was effectively broken in two.
"He was halfway between the two pieces, facing out towards the room with the piece of masonry lying across his chest."
Mr Green said it had taken him and his friend to remove it.
In statements read out to the inquest, paramedics who attended the scene expressed surprise at the way the stone lintel was attached by only three bits of adhesive.
The inquest heard the fireplace had been fitted by company KD Childs for Persimmon Homes.
Lee Astle, who worked for them at the time, said he could not remember if he had fitted the fireplace. He told the inquest he had no qualifications or previous experience working with stone, and had been given no formal training but he had worked with another employee .
The inquest continues.