For decades, Drayton Hall's interpreters have said the current house began taking shape in 1738, when John Drayton bought the property along the Ashley River.

And they said the family likely moved into their grand new home around 1742.

Today, however, that second date has been pushed forward - by almost a decade - thanks to new scientific research known as dendrochronology.

The house museum contracted with Michael Worthington of Oxford Tree-Ring Laboratory to take core samples from the home's attic and analyze when the wood was cut.

By studying the width of the series of rings, and matching them to 18th-century weather records, Worthington was able to conclude the timbers were cut in the winter of 1747-48.

Since the house's attic trusses would have had to be in place for a while before its roof and interior plaster work were finished, the house likely wasn't occupied until the early 1750s, just before the 1752 marriage of John Drayton and Margaret Glen.

"It does not change our interpretation at all: It's still the first fully executed example of Palladian architecture in the United States," says Carter Hudgins, Drayton Hall's deputy director. "If it came out as 1770, we'd be in a different situation."

Worthington estimates he has used dendrochronology to study the age of approximately 450 buildings since he began working in America in 1998.

He has dated wood in The Pre- sidio's officers' club in San Fran- cisco, at John Adams' birthplace in Quincy, Mass., and in the De-catur House's slave buildings in Washington, D.C.

But most of the examples listed on his website are more modest historical homes, barns and other century-old outbuildings.

"Dendrochronology is getting more and more popular, especially now that the recession is over and people are spending again," he says. "I get quite a few people calling me up saying, 'I want to know how old my house is.' "

At Drayton Hall, Worthington used a special drill bit to remove about 20 core samples, each about the size of a little finger. The hole is filled with a wooden peg of the same size.

Worthington says a typical report involves taking between six and 10 samples, analyzing them and then preparing a report, all of which costs about $2,000.

While he often works in basements and attics, Worthington says a major rehabilitation, when walls are removed, can be the best time to collect samples.

Unfortunately, it's not always a success.

Small pieces of wood, especially those that are not very old, can prove difficult to pin down.

"The longer the sequence (of rings), the better chance you have with dating," Worthington says.

Meanwhile, the age of the Lowcountry's oldest buildings can be elusive.

The Powder Magazine on Cumberland Street celebrated its 300th anniversary last year, but that was based on a rich trove of Colonial documents discussing the construction of this public building. Little to no early such evidence survives from most other early homes, so dendrochronology could prove to be a useful took to find those dates.

Hudgins says Drayton Hall's 1742 occupancy date had been based on secondary sources, such as the memoirs of Gov. John Drayton, who said his grandfather had built the house from 1738-42. "That seemed to stick," he says. There was a later mention of Eliza Lucas Pinckney visiting a Drayton baby in 1742, but Hudgins notes that visit could have occurred downtown, or somewhere else.

"The bottom line is that the conception date is still 1738. That's when the dream was born, if you will," he says. "Knowing the 1747-48 dates actually enhances the interpretation because we're asking more questions about the construction sequence and coming to a better understanding of how the house was constructed."

Reach Robert Behre at 937-5771.