The Sonoma County Museum is moving forward with plans to relocate its collection of art and artifacts into a neighboring space long used as a flooring warehouse.

The expansion would allow it to move its collection of about 20,000 objects from a warehouse in Rohnert Park into a temperature- and humidity-controlled archive just east of the 7th Street museum.

The museum has owned the building housing the Conklin Brothers flooring showroom and attached warehouse since 2001. The company's lease expired this summer, and the museum decided not to renew it in order to pursue its expansion.

"Safe long-term housing for the Sonoma County Museum's rich collection of art and historical artifacts has been a high priority for decades," Diane Evans, the museum's executive director, said in a statement. "The decision to take over the Conklin building makes a long-term investment in the cultural history of Sonoma County by ensuring that the museum's collections will be preserved and protected."

The museum expects to spend about $500,000 on the project, which includes both the renovation of the 6,000-square-foot warehouse and upgrades to the existing retail space, Evans said.

The retail space could be leased to a new tenant in the short-term or turned into gallery or programming space in the future, Evans said.

The museum has given Conklin Brothers owner Wayne O'Connor until the end of 2013 to vacate the building. O'Connor said he is in the process of looking for a new location, but thinks it will prove difficult to find a building with good retail and warehouse space.

The museum didn't want to lose the revenue from a long-term tenant, but was forced to make a decision when its own lease on the warehouse space at Sonoma Mountain Village in Rohnert Park expired, Evans said.

Renovation work on the Conklin Brothers building is expected to begin in early 2014.

The museum's goal is to have separate facilities for art and history and a shared facility for collections storage.

Two facilities are needed because the current building is too small and the spaces required for displaying contemporary art and historical artifacts are radically different, Evans said.

The museum still hopes to expand its contemporary art gallery space into the first floor of the 10-story Museum on the Square project planned for the former AT&T building on Third Street.

That would allow its current location in the former post office building on Third Street to be dedicated to the region's history.

Evans said the repeated delays of the Museum on the Square project have created challenges for the museum.

"It's been frustrating. It's been hard to plan, hard to fundraise," Evans said.

The Museum on the Square project includes some storage space for the museum in the basement, but the delays have made it unclear when that space could become available.

The project, first announced nearly two years ago, has had difficulty obtaining financing. Part of the delay stems from the demise of the city's redevelopment agency, which owned the building and had entered into contract to sell it to developer Hugh Futrell. The agency's dissolution has created uncertainty for lenders, investors and title companies.

The city is now proposing a fourth contract extension that would give Futrell until the end of 2013 to close the deal.

The new collection facility is made possible in part by a five-year, $300,000 National Endowment for Humanities challenge grant. It will meet national museum standards for temperature and humidity control and security. It also will contain an area where researchers can examine objects and view collection records, Evans said.

Not all of the 20,000 objects in the collection are expected to make the move. The collection features artworks and artifacts documenting the history and culture of California's North Coast region, but "they're not all jewels," Evans said.

Museum staff are in the process of winnowing the collection down to the most desirable pieces. Up to 20 percent of the collection might not make the cut, she said.

In some cases there are multiple objects of similar type. For example, the collection includes nine washing machines, multiple Singer sewing machines, and some old printing presses that are "greasy and gross," Evans said.