Thomas Jefferson spent more than 40 years designing, building and refining his home. Perched upon a mountain with magnificent views of Charlottesville and the Blue Ridge Mountains to the west and the rolling Piedmont farmlands to the east, Monticello is a most extraordinary house.

But like other homes far less grand, it has a most ordinary problem: a leaky roof.

"The roof has been leaking for years," said Libby Fosso, Monticello's communications officer.

According to John Mesick, who is part of a team of historical architects called in to examine the problem, the main roof should have been replaced 18 years ago. When Mesick arrived in 1987, there were buckets on the floor collecting leakage and "a lot of streaking on the walls and plaster damage," he said.

The Thomas Jefferson Memorial Foundation, a nonprofit group responsible for the maintenance and preservation of Jefferson's Albemarle County estate, is about to fix the roof. The project is the group's "biggest {renovation} attempt ever . . . in terms of complexity, scope, significance, and cost," said Daniel P. Jordan, director of the foundation.

Work will begin next summer and is expected to continue for 14 months at a cost of more than $1 million.

"It is a drawn-out and expensive project," said William L. Beiswanger, the foundation's director of restoration. Beiswanger said the project is "complicated not only by the replacement of the roof, but also {by the replacement} of the balustrade and skylights." The balustrade is a railing that runs along the lower perimeter of the main roof.

From the early 1770s to his death in 1826, Jefferson, a self-taught architect, designed his house and its roof to incorporate all of the latest technology. The roof especially demonstrates Jefferson's ability to "resolve practical problems in an ingenious manner," said Jordan.

Jefferson often redesigned the roof as he redrafted the plans for Monticello, dispatching with traditional European pantile (a roofing tile with an S curve) roofing and experimenting with sheet iron, lead, copper, and chestnut and tin shingles. The house and roof are "a window into how {Jefferson's} mind operated. It shows his concern over the pursuit of technology," Mesick said. They were his architectural laboratory, he added.

Among the innovative designs are "rooflets," roofs with ridges that allow efficient drainage (later used by Jefferson on the President's House in Washington and on buildings at the University of Virginia) and interlocked tin-plate shingles that required no soldering.

Jefferson was intrigued with the idea of tin shingles and spent hours copying instructions on how to cover roofs with them from a borrowed British handbook unavailable in the United States, Mesick said. He designed his own set of tools to fold the metal and link the shingles together. These shingles were used to roof the dome, and several buildings at U-Va.

Jefferson also built skylights; a balustrade; and a Chinese railing, which surrounded the peak of the main roof; and added the oculus (a circular skylight) to the dome.

Because Jefferson's plans were so complicated and Monticello unlike any other building in the area, "he had a terrible time getting skilled craftsmen {in the vicinity}. He had to bring in people from Philadelphia," said Mesick.

Mesick, whose firm, Mesick, Cohen, Waite, also worked on the restoration of Blair House and Mount Vernon, said "This was the most complex roof in America at {Jefferson's} time; the best documented as well. Jefferson kept detailed notes and correspondence with builders, workmen and suppliers" regarding the construction of his house.

The restoration team, using these notes, historic photographs, and remnants of the original roof for guidance, will reconstruct the original design for the roof as closely as possible.

In the mid 1800s, it was discovered that tin shingles were not as desirable as Jefferson had thought. Because the overlap between the layers of shingles on the dome was very small, strong winds forced rain between them, causing leaks. This required constant maintenance.

During the period after Jefferson's death, Monticello, especially its roof, fell into disrepair, prompting observers to remark upon its sorry state.

However, in 1887, an article appearing in Century magazine described the estate as having been "put in excellent order by the present owner," Jefferson Levy.

Levy, the nephew of the man who purchased the house after Thomas Jefferson's death, covered the roof materials with sheet metal and redid much of the exterior, covering up the skylights and removing the Chinese railing. He remained in possession of Monticello until 1923 when the establishment was sold to the Thomas Jefferson Memorial Foundation.

In 1924, Gordon Granger, a local contractor, was hired by the foundation to replace the sheet metal roofs that Levy had put on. For the most part, this is the roofing that remains on the house today.

The foundation replaced the dome's roof and skylights in 1955. Although Monticello has since needed maintenance, only patchwork repairs were made because of insufficient funds, Jordan said.

Recently, workers discovered the original tin shingles from Monticello's dome in a barn. Stored there after the foundation's initial, modest restoration in 1955 and then forgotten, the shingles provide a unique view of the roof's construction.

Because of their age, the original shingles cannot be used in the restoration. Because some of the materials Jefferson used are no longer made and some of the metal combinations have proven incompatible, an exact duplication of the original roof will be impossible.

Unlike the Jeffersonian roofs that lasted no more than a generation, the new roof is expected to last a century. A clinging rubber membrane beneath the shingles will provide the new roof with an impermeable shield against the elements.

Money for the project has not yet been secured, but foundation officials are confident that it will be forthcoming.

"The roof gets you closer to Jefferson," Mesick said.