Police are investigating whether the former occupant of a house where a body was found in Sydney's lower North Shore may have had something to do with the death.

Cleaners started clearing out the Greenwich property on Tuesday and found a mummified body rolled up in a carpet.

Police said the body found this week had been at the home for a "considerable time" and are treating the death as suspicious.

Forensic officers have been sifting through mountains of rubbish as they work to determine the cause of death.

The occupant of the house, Bruce Roberts, died last year, but police believe he may have hidden the body before his death.

Bob and Gayle Meagher have lived next door for 20 years and described Mr Roberts as a loner, a hoarder and a recluse.

"It's creepy and sad, it's just awful that it's next door, very unpleasant," Mrs Meagher said.

Mr Roberts' parents had owned the property and he had lived there for 40 or 50 years, she said.

"He was paranoid about security around the home and had barbed wire," she said.

She said Mr Roberts kept the home in poor condition compared to other homes in the leafy suburb, and she had never seen him open any doors or windows.

"When he died I was really upset and I was worried that we were next door and what could we have done [to help him], but the home was not a very healthy environment, so there was nothing we could have done," she said.

Another neighbour described his as "a really solitary guy, he wore the same thing all the time and just walked up and down Greenwich Road".

Neighbours say the former occupant of the property, Bruce Roberts, was a hoarder. ( ABC News: Mark Reddie )

"He lived alone and was a really routine lonely guy."

Another neighbour, who had lived in the area for six years, described the occupant of the home as "childlike".

"He was [in his] late 50s or 60s, had the same brown jacket on, he was childlike in a way, he just had no expressions, nothing," she said.

"You'd say hello and he'd just mutter 'hello' or just not notice.

"He lived in this tiny little house on the corner, it's completely overgrown and you can see rubbish in the garden."

Another neighbour said the house was "full of junk".

The ABC saw piles of old tyres, wood and cardboard outside the property, which was overgrown with shrubbery.

Witnesses heard items being moved around inside the home as forensic officers worked inside.

Detectives from the State Crime Command's Homicide Squad were called in to investigate the circumstances behind the death.

A post-mortem is being conducted to establish the cause of death and the gender of the deceased.