BIDDEFORD – A New Hampshire couple has purchased the massive Riverdam Mill yard, a 300,000-square-foot maze of connected buildings that is being used by start-up businesses.

Jonathan and Nancy Morse, partners in Boulder Properties LLC of Stratham, N.H., purchased the Saco River complex last week for an undisclosed sum, according to Dan Greenstein of the Boulos Co.

The buildings, most of which are made of brick, were originally built as part of the Pepperell Manufacturing mill.

It was being used as a so-called business incubator by seller Benjamin Gamache of Manchester, N.H. The new owners plan to make some upgrades, but they don’t plan to change the property’s mission.

“They basically bought it as an investment,” Greenstein said. The Morses also own old mill buildings in Sanford and Portland.

Property Manager Jim Fisher said he is looking forward to beginning a series of upgrades on the property.

“We are pulling up carpets and putting wood floors in. We will try to fix up the exterior, and make it look more respectable,” he said. “We will paint, and work on some windows.”

Biddeford Economic Development Director Robert Dodge said the mill yard space serves an important role in the city as a relatively inexpensive alternative for new businesses.

“It has really filled a niche here by providing low-cost space for start-up businesses who couldn’t afford, and don’t need, more expensive real estate in one of our business parks,” Dodge said.