DOWNTOWN LOS ANGELES — The architects working on the $1 billion replacement for the Wilshire Grand hotel today unveiled a new design distinguished by a soaring spire that will be the tallest point of the city’s skyline.

The spire will rise atop the 71-story structure from a sloped, dome-like cap likened to a sail that encloses what officials term a “sky lobby.” That structure will render the tower the first Downtown high-rise without a blocky, helipad friendly roof.

Project architect AC Martin Partners has been working closely with officials from the Los Angeles Fire Department to win the blessing for the roof design, said project designer David Martin.

The structure still includes a small horizontal pad that could accommodate helicopter rescue operations, but it’s a slate of state-of-the-art fire safety infrastructure elements that would allow the tower to skirt the full helipad requirement, Martin said. Chief among the special safety elements is a “hardened” elevator that could function during four hours of fire conditions, said John Starr, a project architect with AC Martin.

The proposed pad is smaller than what city rules require, but AC Martin’s design will satisfy the fire code, Fire Chief Brian Cummings said.

The project will include high-tech LED lighting embedded in the building’s glass “skin,” but AC Martin has not finalized plans on how to incorporate the lights, Martin said.

According to the project’s city approvals, the lights can broadcast advertisements on the lower podium and upper levels, but only non-commercial artistic imagery can be used in between. At question is where to place the lights in the tower — the denser the bulbs, the sharper the imagery, but more lights means a greater expense for a technology that could become outdated quite soon, Martin said.

A 900-room hotel will occupy the building’s upper floors. Beneath it will be 400,000 square feet of office space sitting atop a podium housing retail, restaurants and other amenities.

The building is being developed by Korean Air, a subsidiary of Hanjin International. Construction is slated to start in late 2013, after the razing of the shuttered Wilshire Grand. The new tower is expected to open in December 2016.

The spire will reach 1,100 feet, which is taller than US Bank Tower. US Bank Tower’s highest occupied floor, however, will remain higher than the top level of the Wilshire Grand project.

Contact Ryan Vaillancourt at ryan@downtownnews.com.