SANDRA BENSON sat in her grand double living room with the 12-foot ceilings and two marble fireplaces and shook her head.

"The house across the street was wonderful. Almost untouched, with molding and trim and beautiful doors. The District government came in, tore it all out and piled it in the street and made two units from it. We salvaged what we could. If the new owners want to restore the house, we have some of the pieces waiting for them in our basement."

Sandra and James William Benson have used bits and pieces from houses gutted in the area to restore their own magnificent mansion just off Logan Circle at 1502 Vermont Ave. NW in the five years they've been working on the house.

"The trouble with restoration," said Sandra Benson, "is that after a while you're starting to have to repair what you did first."

The Bensons started out with more advantages than most. They only paid $57,000 for their house. "We thought it was a lot at the time," she said. And they stopped counting when they'd put $175,000 into restoration, not counting all of Benson's hard work. As Benson Builders, he specializes in heating and airconditioning old houses. The two of them buy and restore old houses and resell them.

"It wouldn't be possible," said Sandra Benson, "if my husband was not the greatest craftsman ever. He knows how to do everything. That's how we met. I was restoring a house up on Capitol Hill. Everybody else wanted to tear up my tin ceiling to make a repair. He came and looked at it and knew right away how to save it."

Sandra Benson's other favorite person is Heini Zimmet, the plasterer whose name is a carefully guarded secret amongst the best of the house restorers. Zimmet made arches, restored cornices and a wonderful shaped-plaster base for a wash basin.

The Benson house was divided in to eight apartments when they bought it, plus two more apartments in a sort of a lean-to addition. They tore down the bad wing and made a fine brick patio and barbecue with lattice screen where it had been.

We came into the house up the tall stairway with its elaborate brass railing and flowered sides.

"I brought it here from Puerto Rico," said Sandra Benson, admitting it wasn't original to the Circle. "I first started restoring houses when I was living in San Juan. I restored five there -- the governor's wife and the archbishop came to see one. I've restored about eight or nine here with my husband. When I see a derelict house, I itch to restore it."

Inside the present Benson house, we stood in a much-admired center hall, with a curving staircase leading upstairs, the drawing rooms to the left, the dining room to the right.

A fire in the main house had damaged a wall between front and back parlors, so that went, leaving a spacious 11-by-38-foot double room. In the process of restoration, they found the back parlor had tall double-hung windows designed to serve as a door onto the balcony.

Benson made the wall sconces, piping in gas for two of them. The fireplace mantells were added by the Bensons -- one was made up of five pieces.

Benson put plumbing into the armoire in the living room for a bar. A glass table rests on iron railings, which were once on a balcony in Puerto Rico. A huge fern in one corner is quite appropriate to the age of the house.

The dining room across the way has its own fireplace, of course, and tall windows for east light. The kitchen behind it is the former butler's pantry: small but neat.

Upstairs, the Bensons have a huge master bedroom, with a velvet headboard they made themselves. Of course they have a fireplace in the bedroom, but you might not expect the one in the bath. The bath is one of the best rooms in the house with a huge black tub by the fireplace and shiny brass towel racks. The toilet and bidet have their own closed-off area.

On the top floor, the daughter's bedroom has not only an elaborate mantel but an interesting fireplace, which Sandra Benson says "is really a stove, originally on wheels so you could connect it to the stove pipe in whatever room needed warming." The daughter's bath has a red velvet canopy around the four-legged tub. The guest room will soon have a dumb-waiter, which will rise from the kitchen to serve eye-opening coffee.