WILLIAMSTOWN — After roughly three years of construction, the new $66 million, 78,000-square-foot science building at Williams College is open for business.

The public is invited to an open house Wednesday from 4 to 6 p.m. Visitors are encouraged to enter through the building's main entrance off Bank Street.

The new building, at Walden Street and Morley Circle, houses research and teaching laboratories, shared equipment and shop support spaces, a microscopy suite, and faculty offices for the biology, chemistry and physics departments.

This is the first step in an expansion of the school's science facilities, which is driven by growth in the number of students majoring in the sciences. In 2000, about 27 percent of students were science majors. Today, more than 45 percent of students are science majors, according to school officials.

The nature of science learning has also changed, with new technology and more focus on research and the growth of research involving more than one educational discipline. The needs of a science facility are substantially different than they were at the turn of the century.

"Faculty members are thrilled to continue their research in state-of-the-art facilities with ample space for the hundreds of Williams students who participate in faculty-student research every year," said Chip Lovett, chemistry professor and chairman of the Bioinformatics, Genomics and Proteomics Program. "The new building promises to increase interactions between students and faculty from different laboratories and departments in beautifully designed spaces surrounded by stunning vistas of the Purple Valley."

The entire science center project is expected to be done in 2020 at an estimated cost of $204 million. In 2015, in preparation for the expansion project behind Morley Science Labs, one house was relocated and a second demolished.

The next step is demolition of the Bronfman Science Building, slated for later this year. Another building will be erected in its place, with about 100,000 square feet of classrooms and offices.

The buildings will be in keeping with the college's green-building standards, and while increasing the entire science complex's footprint by 30 percent, they will use significantly less energy than the existing Bronfman building.

The microscopy suite boasts two electron microscopes, a unique feature in a college the size of Williams, noted Michael Wood, senior project manager for the college.

He said the new building contains 31 offices, and 30 labs, plus a variety of support spaces. There are 4 stories.

The machine shop is self-contained and is equipped to repair scientific equipment and even design and manufacture new devices upon request from faculty.

"If it exists, we can fix it," said Jason Mativi, instrumentation engineer. "If it doesn't exist, we can make it. And we get requests from pretty much everywhere."

The shop is equipped with 3-D printers, lathes, a laser cutter, a plasma cutter, wood and metal working equipment, along with a design lab.

New research labs for biology, chemistry and physics are featured in the structure. The new building connects to the Morley Science Labs through a second-story glass-enclosed pedestrian walkway. Shared space in the science center will expand and include four flexible, interdisciplinary labs.

Using design techniques and new conservation technologies, the new science space will have twice the square footage — 150,00 square feet — and use half the energy of the current building, according to information provided by school officials.

Designed by Payette Architects, the South Science Building aims for LEED Gold certification for design and construction. The building has advanced environmental controls that provide temperature and humidity precision required for many research efforts with reduced energy consumption along with the utilization of LED lighting throughout.