Residents living in four homes next to a house declared safe of improvised explosives and other hazards by Barrie police Thursday were asked to leave their homes again after the discovery of an additional cache of hidden chemicals.

Const. Angela Butler said investigators found the chemicals after getting a tip from one of the two men who had been living in the house that teams of police who spent a week scouring the residence had missed something.

"There was something hidden that was not obvious to the officers," she said.

She added the new information led police to a "grouping of chemicals" stuck behind a panel in the basement.

She said people living in four homes sitting beside and behind the 30 Virgilwood Crescent property were asked Friday morning to leave until the evening.

"We need room for the officers to work. We need room for the officers to move safely to get these chemicals out and to remove them."

She said residents in homes across the streets have also been told to stay out of their front yards while officers dispose of the new threat.

Roughly 60 residents living in 20 neighbouring homes were first evacuated last Thursday when the search began.

They were let back one week later after special teams of investigators finished picking through the property.

Butler said they found a total of 83 improvised explosive devices, including pipe bombs, and a quantity of unidentified chemicals.

In addition to the explosives, some of which were detonated on site, police combing through the home have also found 29 firearms including three rifles, two shotguns and a civilian version of an MP5 submachine gun, along with thousands of rounds of ammunition.

Police have said that 10 of those weapons were pulled from an underground fallout shelter running at least 4.5 metres long and more than two metres deep dug into the home's backyard.

A father and his son had been living at the home, which Barrie officials told reporters may be demolished if city inspectors deem it unsafe.

Both men were charged last week in connection with the 34-year-old cold case involving the killing of Michael Traynor, a development that led police to check out the home.

Police say Donald Feldhoff, 54, is charged with first-degree murder in the 1978 slaying.

His 75-year-old father William has also been charged as an accessory after the fact.