The sizable home at 35 Legare St. is like many other old Charleston homes.

It still has a lot of historic fabric - mantels, wooden floors, plaster walls, stairs - but it also has seen a lot of changes since it was first built two centuries ago, such as the vibrant multi-color ceiling fan in a third-floor bedroom.

Sorting through what should be kept, and what can go, is crucial to maintaining its value as a historic home. The process can be tricky, even for experienced architects, contractors and owners.

That's why Historic Charleston Foundation has stepped here in with two of its most important, but perhaps not so well-known, preservation tools.

The foundation recently bought the property with its revolving fund. This tool is a pool of money that it has used for several decades to buy endangered historic homes and then resell them to preservation-minded buyers.

The foundation bought the home last month for $1.75 million, and it's done some painting, roof work and rotten wood repairs. It's currently seeking offers beginning at $1.825 million.

While the foundation can make money on these sales, it has lost money, too. "This is not a fundraiser for us," says April Wood of the foundation. "This is our mission."

The goal isn't to turn a profit, but to ensure the home's long-term preservation, and that's where the foundation's second tool comes in: covenants and easements.

Historic Charleston Foundation already had a covenant on 35 Legare, one signed in 1984, but it was only about one page long. Whoever buys the home next will have to sign a new covenant expected to run about 30 pages.

In addition to requiring the house's upkeep, this legal agreement will address preservation of interior architectural features as well as the bricks and planting beds that survive in its garden, a garden designed around 1961 by noted landscape architect Loutrel Briggs. And it will address whether the property could ever be subdivided (the house is being sold "as is" for single-family use).

These agreements don't necessarily tie the owner's hands, but they will bring the foundation into the discussions about remodeling and major changes, says Katherine Pemberton, the manage of research and education.

"It is always a scary thing when you say 'interior easement,' " she says, "but it's really about protecting the pieces that make the house more attractive and historic."

The 35 Legare St. house is a great example. Over the years, the three-story home has been altered with a mansard roof, piazza enclosures, bay windows and outbuildings.

For years, the foundation had believed the house was built around 1828 as the city was prospering and spilling well beyond its original walls. But foundation board member and historic contractor David Hoffman found evidence that dates the home almost 50 years earlier.

That evidence is one of the home's more humble features: a wooden newel post at the stairs right upon the entrance. Its relatively simple design and craftsmanship are more similar to construction in the late 18th century.

The easement will require this be kept, but the next owner likely will have carte blanche to replace ceiling fans, outdated kitchens and bathrooms, more recent built-in bookshelves and other alterations of more recent vintage.

"Kitchens and bathrooms are often excluded (from these agreements) because they're updated so frequently," says Wood, who manages the easements.

The foundation currently has covenants on 270 properties that it once owned, mostly through purchases in its revolving fund program, which was the nation's first when it began in 1957.

It also has about 110 other easements given by preservation-minded property owners who can qualify for a tax deduction in return. (Easements and covenants are very similar, but when the foundation owns the property and places these restrictions on it, it's called a covenant; when a homeowner agrees to such restrictions, it's called an easement).

About 48 of these agreements protect interiors; the one at 35 Legare will be the 49th. These interior easements are arguably the most important because the city's Board of Architectural Review looks after exteriors.

The revolving fund was key to saving Ansonborough, where the foundation bought, repaired and flipped - with covenants - more than 60 buildings between 1959 and 1976. About 40 others were rehabilitated or restored during that same time, making it one of the city's most desirable neighborhoods.

(The foundation's success sort of priced it out of competition; it once bought homes there for as little as $7,000 and $24,000, and now homes there routinely sell for $1 million and more.)

In recent years, the fund has expanded to help preserve historic homes in low-income neighborhoods or, as in the case of 63 Smith St., to preserve a large garden space that otherwise could be subdivided and built upon.

The foundation soon will bring down fund experts from Boston and Rhode Island for their thoughts on what sorts of preservation successes the fund might enable in the future.

And as with 35 Legare, who knows how many people will pass by one day and think, "What a handsome home" without any clue of the Historic Charleston Foundation's complicated dealings that helped keep it that way.

Reach Robert Behre at 937-5771.