As the steel claws of the construction vehicle crunched a section of the roof of the Chester County Society for the Prevention of Cruelty to Animals, an employee winced.

"I didn't expect to get emotional," said Allison Tilling, 29, of Downingtown, tearing up as she watched the demolition of part of the facility on Phoenixville Pike in West Goshen Township.

Tilling, a nearly four-year kennel technician, said she certainly understood the need for the $1.6 million expansion project that began Tuesday, but she still found the destruction bittersweet.

"There are a lot of memories in there," she said wistfully.

The last time the Chester County SPCA overhauled its facilities, Ronald Reagan was governor of California, the Vietnam War was raging, and the Monkees ruled the pop music charts.

Since 1967, the agency has undergone minor, periodic renovations, said Dennis McMichael, director of operations, but not enough to meet the demand for its services.

Conrad Muhly, the organization's board president, said he did not know how many pets resulted from the county's population growth. (It has grown from 210,608 in 1960 to 498,886 in 2010.)

He said the board has had numerous reminders that the facility needed more space as well as upgrades.

"We still have the old-age open trench drains for waste disposal," he said, adding that the new kennel will include underground piping.

The current one-story facility is 8,000 square feet. Part of it will be torn down and replaced with new construction that will increase the total space by more than 2,000 square feet. The new facility will become more energy-efficient and will blend into its residential neighborhood better, said Kerry R. Haber, the architect for the $1.6 million project.

"Before, it looked like a 100-year-old prison," said Muhly.

The new work will add windows and glass block, and include new dog runs; expanded cat housing; a medical suite for on-site vaccinations, testing, and spaying/neutering; a separate room and cages for other animals; and additional storage and office space.

Haber said completion was targeted for Nov. 1.

In the meantime, the agency - which has been squeezed into the old building section that will also be renovated - is open for business and will continue to accept unwanted animals and investigate allegations of animal cruelty, Muhly said.

Frank Sobyak, the organization's treasurer, said some things it is asked to do were impossible to anticipate. He recalled a request from a bank that had just completed the foreclosure of a pet store and called the agency because it needed to unload dozens of fish.

"We ended up finding homes for a lot of them," Sobyak said.

Agencies outside the county will be called upon if needed for overflow housing.

Founded in 1929, the Chester County SPCA is an independent nonprofit that does not receive county, state, or federal funding. The agency has contracts with all but a handful of Chester County municipalities, which pay a nominal fee for the services they use, Muhly said.

The bulk of the agency's funding comes from donations and events such as the forthcoming Forget-Me-Not Gala, an outdoor garden party that features a horse-and-carriage parade, a gourmet buffet, and silent auction.

Muhly, who called "the generosity of animal lovers in Chester County" the agency's lifeline, said pledges had covered about half of the $1.6 million expansion project so far. He said he hoped the gala would make a dent in the remaining debt.

The 2011 Forget-Me-Not Gala will be held June 12 from 5 to 8 p.m. at the Marsh Valley Farm in Glenmoore. This year's special guest is Laura Wiess, a native of Milltown, N.J., and author of young-adult fiction.