Protesters walked through two open access points, then cut their way into a restricted construction zone before unfurling a banner on a Parliament Hill rooftop in December, the Mounties said Thursday.
The incident raised serious questions about security in the nation's capital.
An RCMP review says Greenpeace activists wearing construction hard hats and coveralls were able to reach the roof of West Block via scaffolding at the rear of the building.
The area was surrounded by a fence secured with nylon tie-wraps, which they cut early in the morning of Dec. 7 before climbing onto the roof and unfurling a banner urging leaders to address climate change.
Other protesters climbed onto the roof above the Senate entrance to Centre Block and displayed banners denouncing the Alberta oil sands.
RCMP, Ottawa police, Ottawa fire department and Parliament Hill security all responded to remove the 20 protesters, who now face mischief charges.
The administrative review calls on authorities to examine both short and longer term security strategies on Parliament Hill and increase the RCMP's already imposing security presence.
It also urges additional security measures on Hill construction sites, where renovations have been ongoing for at least a decade.
The review has led the national police force to re-examine its operations, improve security and "validate the need for longer term enhancements," said Chief Superintendent James Malizia, the officer in charge of protective operations in the capital region.
The report stressed the need to balance security measures against the need for public access.
"Parliament Hill is a symbolic place for all Canadians and international visitors," an RCMP statement said.
"The RCMP and its security partners remain committed to providing a seamless and comprehensive security package both on the grounds and within the parliamentary precinct."