It's one of the first questions that occurs to a visitor at George Washington's Mount Vernon estate: How much of the mansion really dates back to Washington's time, and how much has been replaced?

The estate is in the midst of a project that will help answer that question, down to every nail in the floorboards.

Architects and preservationists are at the estate building a computerized database of every piece of the mansion. Laser scans are recording three-dimensional images to the tiniest detail, and workers are crawling on their hands and knees to photograph and document key components.

Combined with the already meticulous records that Washington himself kept of his work on the mansion, as well as those over the last 150 years since the estate has been in the hands of the Mount Vernon Ladies' Association, the model will provide a comprehensive database that the estate will use to guide future restoration efforts.

For example, Mount Vernon will soon have to put in a new fire suppression system that by necessity requires installation of new sprinkler heads to guard against the catastrophic. The database will guide that installation process to ensure that the installations occur with a minimum impact on the oldest parts of the house, said Thomas Reinhart, the estate's deputy director for architecture.

"Every screw, every nail driven into this home — we want to know the impact on the long-term preservation of the structure," Reinhart said.

The project has already yielded some new information about the home as well. For decades, preservationists have waffled on whether the floorboards in the estate's signature New Room were the same that Washington himself installed and walked on. Reinhart says now that the boards clearly are the originals — a conclusion they reached in part through careful examination of the 2,556 nails in those boards.

A close look at the nails and the nail holes reveals when they were made — on a very basic level, the old nails leave square holes and newer nails leave round holes. Construction techniques were different in various eras, as well.

After reviewing the nails, the documentary evidence, and the other details assembled in putting together the database, Reinhart was able to conclude that the boards — high-quality southern yellow pine that "is hard as a rock" as it dries over the decades — are indeed the originals, but they had been rearranged and reinstalled at some point in the 19th century.

It's difficult to quantify exactly how much of the mansion material dates to Washington's time, and the project, once completed, will provide a better picture. Generally, though, Reinhart said the estate was forward thinking in its preservation tactics, back to the days that the Mount Vernon Ladies' Association assumed control of the estate back in the Civil war era.

Even back in the 19th century, Reinhart said, restoration work was done with a nod toward preservation — plaster repairs, for instance, were done with an effort to keep as much of the original in place, and replace only what was absolutely necessary.

Reinhart said he hopes the project will shed additional light on the history of the mansion before Washington himself owned it. Washington's father built the home in 1735, and it subsequently underwent a series of expansions.

About 1 million visitors a year visit the estate.