CLEVELAND, Ohio - After nearly a decade of planning, design and redesign, the Cleveland Museum of Natural History will begin construction this spring on the first part of a five-year, three-phase, $150 million expansion and renovation.

The project is aimed at giving the nationally respected institution a sustainable, light-filled, high-tech home better suited to its mission and collections than the dowdy, architecturally dull, midcentury complex it occupies on Wade Oval, where it has grown through accretion since 1958.

"I think it's going to completely transform the experience of all of our visitors," Evalyn Gates, the museum's director since 2010, said of the expansion project in an interview Thursday.

"It will play a leading role on a national level in terms of what natural history museums can and should do for the public and the understanding of science."

Gates said about a third of the total project cost has been raised so far, (up from $39 million last year) and that the museum has cash in hand to start the $20 million first phase, which includes construction of a 300-space parking garage off East Boulevard on the north side of the complex and a new Perkins Wildlife Center on its south side, off Jeptha Drive.

The cost of the project will be $25 million more than estimated three years ago.

Designed by the nationally respected Denver architecture firm of Fentress Architects, with a team of consultants on exhibits, sustainability and other specialties, the project will involve tearing down about a fifth of the museum's existing, 230,000-square-foot complex, and then rebuilding and expanding the footprint.

Renderings released exclusively to The Plain Dealer show that architectural features of the Fentress design include a glassy lobby trimmed in stone to resemble a giant fault block rising out of the earth, and a new, two-story dinosaur gallery that will make fossilized and facsimile skeletons of the prehistoric beasts visible from Wade Oval Drive.

Unlike the Cleveland Museum of Art, which had to close for nearly a year in 2006 to keep its eight-year expansion and renovation on time and on budget, the natural history museum plans to remain open throughout its project.

The museum will keep visitors pumping through its complex during construction with a series of special exhibitions on topics such as the world's largest dinosaurs, starting in June, and "The Power of Poison," which will follow.

Gates said the museum would also make its physical transformation visually accessible to visitors so they can watch construction in process.

The project is aiming for Gold certification under the U.S. Green Building Council's LEED program, short for Leadership in Energy and Environmental Design.

When finished, the 300,000-square-foot facility will encompass several new features: a permanent exhibit and laboratory area on the north side of its complex, plus a multipurpose assembly hall capable of seating 500, along with an Ohio Gallery on the region's natural history, connected to the relocated outdoor Perkins Wildlife Center.

The wildlife center, which functions as a pocket-sized zoo of rescued creatures native to Ohio, will include an elevated tree-canopy trail.

A cafe near the museum's main entrance will include an area for outdoor seating in good weather that will be the only institutional eatery directly facing Wade Oval Drive.

The interior exhibit galleries at the natural history museum will increase 78 percent, from 29,700 to 53,100 square feet, including a series of "science studios," where visitors can interact with docents, educators and scientists through lectures, demonstrations and hands-on experience.

In terms of content, the exhibits will trace the history of the Earth from the origins of the universe in the Big Bang through the emergence and evolution of life to man's impact on the planet, including the realities of climate change and its human causes.

When asked about the museum's position as an arbiter of scientific facts at a time when some question evolution or the causes of climate change, Gates, who holds a PhD in theoretical physics from Case Western Reserve University and whose research has focused on astrophysics, said the museum's task is to ensure that the conversation is "not hijacked by other interests."

"Evolution is real, climate change is real and caused by human activity," she said. "We aren't going to back away from our best scientific understanding. We want to be a trusted source, where you know you can come in and get the facts, the latest understanding, in a way that will be respectful of people's intelligence."

Gates said that the goal in designing exhibits is not to preach or scold, to but encourage curiosity, wonder and a desire to learn more.

The museum intends to present plans for Phase 1 to the Euclid Corridor Design Review Committee on Thursday, March 19, and then the next day to the City Planning Commission, whose approval is required for a building permit.

The second phase of construction, including the new exhibit and lab areas, is to occur in 2016-19, and the final phase is set for completion in 2020, in time for the museum's centennial.

In addition to improving the museum's fundamental appeal and revising its permanent exhibits, Gates said the project is necessary to safeguard collections of organic and inorganic specimens that are subject to long-term harm from changes in temperature and humidity.

"To properly care for our collections, we definitely need to improve the climate control," she said. "I would say it's adequate right now, but barely, to be honest with people. It's not long-term viable. We cannot continue to care for our collections in this way."

Inaugurated in the Hanna and Brown mansions on lower Euclid Avenue in 1920, the museum moved to University Circle in 1958 when its original homes were demolished to make way for the Inner Belt freeway.

The museum grew with a series of expansions in 1956, 1977 and 1988, followed most recently by the Shafran Planetarium in 2002, the shiny, copper-colored cone added just north of the museum's current main entrance. The planetarium will remain part of the museum as part of an expanded area dealing with the origins of the universe.

Today, the institution is considered a top 10 natural history museum in the United States in terms of endowment, size of collection, attendance and other factors, Gates said. The institution draws and average of 260,000 visitors a year, and has 5 million artifacts and specimens in its permanent collection.

Inside the museum's exhibit galleries are some displays that haven't been updated since the 1970s. Another concern is that laboratories used by 11 curators with doctorates in their specialties are buried deep in windowless levels that one employee called "the bowels" of the museum.

Gates wants to bring the labs upstairs and place them next to main exhibit galleries, with the five "science studios" sandwiched in between.

The museum is proud of its long and distinguished record as a research institution that has notched major discoveries recorded in professional journals and cover stories in the respected journals Science and Nature. Chief among them is the finding of "Lucy," a 3.2 million-year-old human ancestor.

The museum's project will be the latest in a series of nonprofit institutional transformations in Cleveland over the past two decades.

These include the renovation and expansions of Severance Hall, home of the Cleveland Orchestra (2000), the Cleveland Botanical Garden (2003), the Cleveland Institute of Music (2008), the Cleveland Museum of Art (2013) and the Cleveland Institute of Art (expected later this year).

Foundations and individual donors have dug deep at a time when some studies show the number of those in a position to give is declining.

Nevertheless, the natural history museum believes it can tap donors interested in science, above and beyond the circle of those who give generously to arts institutions.

Growth can present risks. Three years after finishing a new home on Euclid Avenue in 2003, HealthSpace Cleveland, formerly the Cleveland Health Museum, had to sell the building to the Cleveland Clinic to settle debts and saw its mission, programs and remaining endowment absorbed by the natural history museum.

The museum has a $150 million endowment from which it draws $6 million a year, or half its operating costs, a ratio considered excellent in the field, Gates said.

She said the museum's trustees would approve each phase of the expansion project only after 75 percent of the needed funds have been raised.

"We're committed to building on the strong financial foundation of the institution and moving forward in a financially responsible way," she said.

More than anything, though, the museum wants to better serve the public by making its exhibits and programs more relevant and accessible.

"You want to get people thinking," Gates said. "That's the most important thing."