In the story "He Did It Himself" in Saturday's (Dec. 7, 2002) Real Estate section, Jonathan Gaffney's age is incorrect. He is 41, not 47.

Jonathan Gaffney received his first and last formal lesson in handling tools in a seventh-grade shop class. But that didn't stop him from designing and building a two-story addition to his Crystal City bungalow more than 30 years later.

Now, a month after getting his final inspection certificate, the 47-year-old is still somewhat astounded at what he accomplished -- doubling the size of the house.

Even more impressed are some of his neighbors, such as Don Grissom, who lives next door. Grissom has seen lots of renovations and tear-downs in the once-modest community of Aurora Hills, a few blocks from busy Route 1. Like many neighborhoods in South Arlington and elsewhere in the region, it is rapidly gentrifying.

"What is so unique, and amazing, is that he has done it pretty much himself, and he's not a builder or contractor," Grissom says.

Actually, Gaffney is your basic Washington white-collar worker. He is vice president for communications at the Metropolitan Washington Airports Authority. His degrees are in health administration and international affairs.

"Watching him for the past year, I have seen him dig his own foundation, lay concrete blocks, frame it, install his own siding and windows and -- incredibly -- do his own electrical, plumbing and air conditioning," Grissom says. "I have been inside, and I don't believe that a contractor could have done better. It is really quite a story and the talk of the neighborhood."

The exuberant executive became his own architect, contractor and chief laborer in the spring of 2001. He did it, he says, basically because he was in a hurry to accommodate a growing family and could not find a contractor.

He was in a hurry because his wife, full-time Navy Capt. Tracy Malone, had had twin boys, Coury and Kelly, that February. With Gaffney's daughter, Whitley, 12, sharing the space, the three tiny bedrooms, upstairs bath and half-bath downstairs were getting very crowded.

Gaffney and Malone thought briefly about selling the 1925 Sears bungalow that he bought for $218,000 in 1988. The 1,244-square-foot house had character, but very few closets and a tiny kitchen. The "master" bedroom was so small that shelves had been built into the walls around the double bed for storage. A wall bumped out into the space, leaving little room for anything more than an ironing board.

But the couple decided to stay because "neither one of us wanted a commute," Malone said. She works at the Pentagon, and his office is at Reagan National Airport.

Trouble was, the couple could not get any bites from contractors. Using a computer-assisted design program, "we put together a very basic three-page plan of what we wanted and took it with us to a couple home shows to meet builders," Gaffney said. But, even with the babies in their double stroller as a testament to the need to expand, "we just couldn't get anybody to respond."

The firms Gaffney reached that spring said they were booked for nine months. The one bid Gaffney got, for $165,000, was for adding 25 percent less space. "To me, that just seemed kind of high," he recalls.

So Gaffney, an unusually organized can-do kind of fellow, thought he would give it a go. He figured he could handle the box-like three-story addition he had in mind. After all, he had seen his own dad build a house "with some help" when he was a child. His brother has done one, too.

Gaffney also had built a two-story garage for the bungalow in 1994, with white vinyl siding and black shutters. But he notes that it "was just a shell" added to the old foundation, without heat, plumbing or air conditioning. Malone uses the second floor as an exercise studio.

Still, he figured that if he got into trouble along the way, he could just stop and get outside professional help. More about that later.

Do-it-yourselfers are fairly common for many of these same reasons, according to Harvard University's Joint Center for Housing Studies. About 40 percent of home improvements projects are undertaken by the owners, the center says. Most often the weekend warriors are younger married individuals, with cramped houses and tight budgets, said Kermit Baker, director of the center's Remodeling Futures Program.

Perhaps surprisingly, he said, they are not doing just the easy stuff, but also major renovations. Generally, though, they take a lot more time to do the work than professionals because they are not paying for labor, experts say.

The only thing do-it-yourselfers routinely avoid, Baker said, is "the specialty subcontracting," such as roofing and electrical.

As the U.S. population has aged over the past decade, though, the percentage of do-it-yourselfers has slipped. Older and single homeowners are much more likely to hire a contractor, according to the center's data.

The center also sees an emerging "buy-it-yourself" market, where owners purchase products from home improvement centers and then hire a contractor for the installation.

Each time Gaffney sought help from professionals, though, he could not find any.

"I did not want to touch the plumbing, air conditioning and electrical. I didn't want to do it," Gaffney recalls. "But you couldn't get people to come out."

So he consulted books, the Internet and friends with building expertise at the airports authority.

What he did not know, he would learn. For the plumbing work, "he'd go down in the basement and practice soldering," Malone says.

"I went to Home Depot and bought tons of little fittings, and soldered them," Gaffney says.

For the electrical and heating work, he studied texts borrowed from friends or the library.

In retrospect, he says, the plumbing and electrical work "were very easy, a matter of very common sense. . . . This whole project very much appealed to my sense of logic."

His wife, however, suggests that some revisionist history is already underway. "There were a few expletives" coming up from the basement as he worked on his soldering skills, she says. "I hear him say how easy it was now and I remember him saying, 'I can't do this.' "

The proof, though, is in the pudding that is served in the new eating nook.

In the end, Gaffney added 1,180 square feet of living space. The second-floor addition includes a huge master bedroom and bath, with a whirlpool bath, shower, toilet and double sinks. A spiral staircase leads to a third-story loft/retreat for Malone.

On the first floor, Gaffney added a large living room, with built-in bookshelves. (The old living room will become his library.) Off the existing kitchen, he added a pantry on one wall and space for an eating area. Next to that he added a countertop with bar stools.

Because of the engineering and expenses that would have been involved, Gaffney left most of the original structure alone, tearing off the back wall and leaving the existing staircase. He linked the addition to the existing house upstairs through a window that he converted into a doorway and downstairs through the opened back wall.

He did not touch any load-bearing walls in the old house. "When we decided to do it ourselves, we knew it had to be very simple," he says.

Gaffney's success, his wife says, is because of his organizational skills. "He is a man of lists."

He can, therefore, document all his work.

For example, he says the project took about 1,100 hours (until he gave up counting), including just about every weekend from October 2001 to May 2002 and from September to October 2002.

He also worked two to four hours, three to four nights a week, starting before dinner and breaking only to eat and put the twins to sleep.

Though he and his wife were working extra hours because of the 2001 terrorist attacks, Gaffney says there were major practical reasons to jump back to work quickly after Sept. 11.

"I poured myself into it because we had no back of the house. We had torn off all of the siding. And we had ordered about $7,000 worth of windows just before Sept. 11. . . . If we had waited , I bet you we would never have done it."

Gaffney estimates he made 270 trips to hardware stores.

Total cost: $45,649.77, he says. That compares with his original estimate of $37,000. He returned $2,569.43 in merchandise.

It is not clear how much a professional would have charged because contractors' labor charges vary widely. But Harvard's studies suggest the labor would have been at least equal to the materials cost.

Walt Stoeppelwerth of HomeTech Information Systems Inc. in Bethesda, who calculates construction costs, has not seen the work, but he says the job might have cost $105,000 to $125,000, including the spiral staircase, Palladian window and other special touches.

Gaffney says his family was fundamental to his success: "You have to have a family structure that is flexible. It was very much a family effort."

Daughter Whitley, for example, endured countless trips to the hardware store. "I go to school in Burke, and we'd stop at the Home Depot there every day after school," she recalls. The two stopped in so often that "we got to know all the people there. And they'd ask us how the house was going."

Whitley mixed concrete, put up siding and wielded the hammer and nail gun, with supervision. "Everything he did, he explained to me," she says.

Wife Tracy also endured, despite working 11 p.m.-to-7 a.m. shifts at the Pentagon in the weeks after Sept. 11, 2001, and despite being awakened on many weekends by the sound of the hammer, air compressor or other tools. (The twins went to day care when possible.)

Gaffney still seems amazed that it all worked out. He recounts how "intimidated" he felt during his first visit to Arlington County's Department of Permits and Inspections and how "shocked" he was when the county approved the plans without revisions in August 2001. He had done the drawings himself, asking a friend at the airport to "take a final look" before submitting the plans.

The county proved to be a major help, he says, offering valuable advice during required inspections along the way.

Homeowners in Virginia are required to get permits for certain remodeling projects, and the work must pass inspection, but they do not have to be licensed if they do the work themselves, according to county regulators.

Homeowners are required to submit a "plumbing riser" diagram with their plans if they do not hire a licensed plumber, Arlington County construction codes supervisor Richard Ries says. Such a diagram shows where water and waste lines will run.

Homeowners in the District, by contrast, must be licensed to do electrical and plumbing work beyond a limited scope of activities. Montgomery County has an open-book test for do-it-yourselfer electricians, to make sure they are ready. Those homeowners doing major additions in Montgomery and Prince George's counties need plumbing licenses, according to the Washington Suburban Sanitary Commission. (For more information on requirements in these or other areas, consult your county's permitting offices or Web sites.)

Ries says that only 1 to 2 percent of Arlington homeowners coming in to get permits do their own electrical and plumbing work. And he thinks a lot fewer county residents are tackling big projects than the Harvard studies suggest. He figures the do-it-yourself share of home improvements is more along the lines of 10 percent than 40 percent.

"The people who do it either enjoy doing it or don't have the money" to hire contractors, Ries said.

Harvard's Baker notes a "do-it-yourself gene theory" that seems to square with Gaffney's inclination to take the plunge. "There are some folks that'll do it 'cause they're sort of inclined to do it. They enjoy the challenge and they enjoy working with their hands," Baker said. "Then there are other people who won't even attempt to touch it."

Gaffney got in with both hands. After removing the deck ( a "really gross job; I almost quit then," he remembers), he took off the back wall of the old house.

He dug out space for a three-foot-deep foundation with a rototiller. He laid the concrete blocks and poured the concrete foundation. He ordered the lumber and the windows. With help from some day laborers, he framed out and closed in the house.

He installed the vinyl siding and designed and installed the electrical and plumbing systems. He installed the insulation, the air-conditioning ductwork and air conditioning. He calculated the heating needs and ordered and installed eight new cast-iron baseboard radiators. Then he connected the new radiator zones to the existing furnace.

He installed the drywall, with some help from a friend, painted and installed the doors, painted the walls and moldings, put up wallpaper in the new master bath, laid the vinyl floors, designed and built a small side entrance with steps and porch, and ordered the dumpster and cleaned the yard.

The only jobs he did not do were shingling the roof, hooking up the air-conditioning compressor to the air handler, relocating the utilities and mixing the concrete for the footings. And he "broke down" and rented a lift for one day to put the siding on the highest portions of the house. Also, the mechanical plans had to be signed off on by an engineer.

His work resulted in yet another list -- of injuries. They included a severe puncture wound in his right palm, from the demolition; bursitis in his left elbow, from lifting concrete blocks; and a lacerated fingertip, from a power saw being used to finish up the floor molding.

The power saw accident really gets to him because he was so close to being done. He resisted treatment, his wife says. "He's lucky that he has a nurse for a wife because he wouldn't go to the emergency room," she lectures.

Now that the big work is over, Gaffney says all that is left is adding a deck to the addition. But he is not one to stop planning. "I'm sure I'll find something to do," he says.

Meanwhile his daughter's homemade sign on his homemade fence tells the story best. It is a carefully painted picture of a house with the words "Daddy's Builders."

Jonathan Gaffney admires the master bedroom in his home-made addition to his Crystal City house. It took a year and hundreds of trips to the hardware store. For Jonathan and Tracy Gaffney -- holding twin boys Kelly and Coury, 22 months old -- and their daughter Whitley, 12, the new addition became a yearlong family project.