The garage, with its big back window overlooking Lake Illawarra, was Mr Stewart's beloved man cave; a place he would spend hours tinkering with repair jobs.

The couple was watching TV about 8pm on Tuesday when a neighbour knocked on their door and told them, "there's smoke coming from the backyard".

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"It was coming out from the eaves of the garage," Mrs Stewart told the Mercury.

"James touched the garage door and it was hot. He lifted it a little bit and then there was black smoke and flames everywhere."

"It was probably five minutes, and then it was sky-high. I thought the house was going to go because the flames were just sky-high."

Neighbours trained hoses on the blaze, trying to get it contained while they waited for firefighters.

Fire crews were able to extinguish the blaze before it spread to the house or neighbouring properties.

The Stewarts, with dog Mengi, were allowed to return to their home but had a sleepless night, thinking about what could have been.

"We were lucky it [the fire] wasn't later," Mrs Stewart said. "If everyone had been asleep ... "

"We wouldn't be here," Mr Stewart finished.

The garage was completely gutted in the blaze. Lost to the flames was an expensive self-propelled lawnmower and whipper snipper that Mr Stewart had gifted his wife six weeks earlier.

Also inside were tools Mr Stewart had inherited from his father.

"It was his man shed. We didn't put the cars in there because he had a workshop in there - and now it's all gone, Mrs Stewart said.

"He had all our receipts and manuals kept in a plastic folder ... in the garage."

Fire authorities later told the couple the blaze was the result of an accidental electrical fire, likely started by two wires coming apart and rubbing together.