The architects behind a much-maligned addition to Ottawa's Château Laurier are hoping the fourth time is the charm for winning over critics of its modernist makeover of the historic hotel.

The latest version of their design was released on the city's website Wednesday.

It features more limestone "to break up and add visual interest," according to a heritage memo released as part of the proposal.

The memo describes vertical "fins" of limestone facing Major's Hill Park.

The latest design features limestone 'fins' facing Major's Hill Park, according the the architect. (architectsAlliance) The east facade, facing Mackenzie Avenue, and the west facade, facing the Rideau Canal, feature diagonal glass planes framed by more limestone.

"The proposal conserves the cultural heritage values and attributes of on-site and adjacent heritage properties," ERA Architects wrote in the memo.

Previous designs panned

Three previous designs were generally met with contempt from both heritage experts and the public at large.

The first attempt, released in September 2016, was dismissed as too tall and described as resembling "a series of barcodes."

The architects returned two months later with a design that was widely panned for being too similar to the first, and mocked by one critic as looking "like a Travelodge has rear-ended a castle."

The backlash against this first design was swift and fierce. (Supplied)

The third attempt came in February and featured an eight-storey pavilion clad in white steel and glass, separated from the original building by a courtyard.

It, too, drew fire, this time for resembling a "glass box."

Critics also cast stones at the third attempt, a separate pavilion clad mostly in glass. (Larco Investments)

New design 'really a modification'

Heritage Ottawa president David Jeanes said the new design responds to some of those concerns, but only "in a limited way."

While the latest version seems to address some specific worries over sight lines, for example, other issues remain.

"The new design is really a modification of the three earlier designs," Jeanes said.

Heritage Ottawa hasn't released its official opinion on the new design.

In a written release, the city acknowledged the public's concerns about the contemporary design, but said the Ontario Heritage Act doesn't prescribe such details when it comes to additions to historic buildings.

"In fact, heritage conservation practices in Canada encourage additions to heritage buildings to be of their current time," the city noted.

Another rendering of the latest design. (architectsAlliance) This fourth attempt will need to win a series approvals at City Hall before construction can begin. City officials will get their first chance to publicly debate the design on June 18 at a meeting of the built heritage sub-committee.

After that, the proposal will go before planning committee and city council.