While filming a 40th anniversary special for “This Old House” recently, Bob Vila, the show’s original host, stopped to consider why, after all these years, people still can’t seem to get enough of home improvement shows.

“This Old House,” which began chronicling home renovations in 1979, was one of the first such shows to air on national television and arguably helped create the DIY nation we all live in.

“It’s like cooking,” said Vila, who is now 73 and spends his time sitting on the boards of various nonprofits, living mostly in Palm Beach, Florida, and occasionally on the Upper East Side and Martha’s Vineyard.

Say you want to rip out your bathroom linoleum and replace it with ceramic tile. First, maybe you get inspiration from TV; next, you binge a bunch of random YouTube videos or find a how-to video on ThisOldHouse.com or Vila’s website, BobVila.com. Armed with your shopping list, you head to the store, get your ingredients, come home and lose a weekend laying a floor.

“At the end of the project, you’re a hero,” Vila said.

Four decades after Vila and the rest of the original “This Old House” crew introduced viewers to the concept of watching contractors turn tired homes into pretty ones, knocking down walls is big entertainment. “This Old House” is a powerful brand with a magazine, a website and a spinoff, “Ask This Old House.”

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The show’s creator, Russell Morash, whose credits include “The French Chef” with Julia Child and “The Victory Garden,” was crowned the “father of how-to television” by the National Academy of Television Arts & Sciences when it awarded him a lifetime achievement Emmy in 2014. His brand of educational television paved the way for a genre of reality TV centered on what would otherwise be mundane tasks.

Now the competition is stiff. Renovation-hungry viewers can tune in 24 hours a day to HGTV’s endless loop of angst-ridden shows, including “Love It or List It” and “Flip or Flop.” Other networks, including Bravo, have their own high-drama renovation lineups, with shows like “Buying It Blind” and “Flipping Exes.”

But “This Old House” didn’t originally follow the formula of the anxious homeowner saved by a crew of knowledgeable tradesmen that has come to define the genre. Its first season, which aired on WGBH Boston, a local public television station, had no homeowner at all. Instead, it chronicled the restoration of a vacant and dilapidated Victorian house in Dorchester, Massachusetts, that the station bought and later sold. PBS picked up the unlikely hit show the following season, and in 1982, producers featured a homeowner restoring a Greek Revival house in Arlington, Massachusetts. After that, the formula took hold.

To find the right house, the show accepts proposals from homeowners, architects and builders, selecting homes based on the scope of work, budget, timing, style and location. (Vila said that Morash particularly liked houses in warmer places, like Santa Barbara, California, where a winter spent on location would be more appealing than in cold New England.)

There have been changes over the years. Scenes are shorter, and features like “sweat equity,” where homeowners strap on a tool belt and get to work, add drama.

The houses are different, too. One Rhode Island house featured in 2018 was described as an “idea house,” with vacation-focused elements like a plunge pool, barbecue station and outdoor shower.

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But despite the competition from flashier cable TV shows, “This Old House” has largely stuck to its formula, with a cast that includes members from 1979 who still work on one house over multiple episodes.

And it’s a formula that continues to work. In the first quarter of 2019, “This Old House” reached 2.043 million households, and “Ask This Old House” reached 1.876 million households, making them the two top-rated shows in their category, beating HGTV’s entire lineup, according to Nielsen data provided by “This Old House.”

“What HGTV is doing is great, but we look at this content in a different manner. We don’t redo a house in one episode,” said Dan Suratt, chief executive of This Old House Ventures. “People want that level of detail, and that’s what’s lacking in the other shows.”

In other words, rather than a 30-second shot referring to insulation, “This Old House” viewers get an in-depth primer on choosing and installing it.

Vila, who left the show in 1989 over a dispute about his celebrity endorsements, could be credited with creating the handyman-hero aesthetic: the rumpled, but somehow polished workman in a flannel shirt, jeans and work boots. That uniform has come to be synonymous with home improvement television, with variations worn by current HGTV stars like Jonathan Scott of “Property Brothers” and Chip Gaines of “Fixer Upper.”

“Bob inspired an entire generation of industry professionals — I was one of them,” said Gaines, who is starting a new TV network in 2020 to replace Discovery’s DIY Network, with his wife, Joanna Gaines. “He single-handedly shifted the narrative of an age-old trade.”

By the 1990s, Vila had his own show, “At Home with Bob Vila,” and was making periodic cameos on the sitcom “Home Improvement,” where Tim Allen played the fictional host of a show called “Tool Time” and Vila played his rival.

To celebrate the longevity of “This Old House,” PBS recently turned an Upper West Side brownstone into a temporary set for an anniversary special that will air next month and that brings Vila together for the first time with his successors, Kevin O’Connor, the show’s current host, and Steve Thomas, the host from 1989 to 2003, for a round-table discussion. The show will also include interviews with past homeowners and footage from some of the episodes.

Yet even from the start, “This Old House” wasn’t entirely about boilers and knob-and-tube wiring. It has long dabbled in the celebrity cameo.

In an episode that aired on New Year’s Eve in 1983, Vila visited the new Trump Tower in Midtown Manhattan, with Ivana Trump providing a tour of a model apartment. Wearing a royal blue dress draped with a scarf, she pointed out the mirrored walls, lacquered finishes and a mural with 24-karat gold details. “As you can see, all our clientele are black-tie people, very sophisticated people, and this is the feel that they like,” Trump said.

“Ivana has this marvelous accent and was this beautiful woman,” Vila recalled. “She kept saying, ‘onyx, gold, silk.’ I’ve never forgotten it.”

A young Donald Trump then walked Vila through the atrium, explaining the scope of his investment. “When you’re going to spend the kind of money that we’ve spent — where we’ve spent for the finest marble, for the finest bronze, for the finest everything else — you have to be careful,” Trump told him.

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Vila remembers being underwhelmed by his encounter with the future president. “How shall I put it without being castigated?” he said. “It was not exciting television.”

Over the years, dozens of homes have gotten the “This Old House” treatment. And for some of those homeowners, like Terry and Sima Maitland, the experience of a season spent on television was as memorable as the improvements themselves.

In the early 1990s, the couple and their three children were living in a cramped 1710 house in Acton, Massachusetts, with oddly shaped rooms, virtually no closets and a tiny kitchen in need of new appliances. Also, the pipes repeatedly froze, bricks were crumbling and falling into the chimney flues, and the only bathtub would not drain.

“We always had this fantasy that ‘This Old House’ was going to come and save us,” recalled Terry Maitland, 71, a real estate broker who still lives in the house with Sima Maitland, also 71, a retired teacher.

So the Maitlands sent the show a letter, begging for help. Eventually, a producer called, and then a location scout paid them a visit. Their $150,000 renovation became a subject of the 1994 season. Like other homeowners featured on the show, the Maitlands paid for the renovation, but they got deeply discounted materials from companies angling for a mention of their products, resulting in a higher-end renovation than they would have had otherwise.

The season chronicled Tom Silva, the show’s longtime general contractor, building an addition that expanded the house from 2,200 square feet to 3,400. The addition made room for a new kitchen, family room, laundry room, powder room and a master suite with a bathroom.

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Twenty-five years later, the Maitlands have made few changes to the house. “Still, every time I come up the driveway I can’t believe we live here,” Terry Maitland said.

Not all the show’s guests have been eager participants. David and Janet McCue knew little about the show and had no interest in appearing on it when they were approached in 2001 by Thomas, a member of their yacht club. A mutual friend introduced them, telling Thomas that the McCues were planning to restore their 1883 shingled waterfront house in Manchester, Massachusetts, which had been stripped of much of its character during a previous renovation.

“It looked like a motor hotel in Hyannis,” said David McCue, 65, the founder of McCue Corp., a safety equipment manufacturer. (Janet McCue, now 60, who worked in the fashion industry, is retired.)

Initially, David McCue rejected the offer, as the couple had already renovated five homes and had no interest in doing this one publicly. “I can’t imagine doing this on TV,” he remembers thinking. “I wouldn’t want a camera in my face.”

Then a producer paid them a visit. “He was utterly charming, and our ‘no’ went to ‘maybe,’ ” David McCue said. The next day, the McCues received a delivery: a box of videotapes of past episodes, with a note that said “homework.”

Soon after, the McCues met with Morash and Silva, and were finally persuaded. “Russ was known as awfully crotchety. But I didn’t mind; I grew up in England with crotchety people,” David McCue said. “I thought he was great and authentic and real and didn’t mince words.”

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And so the McCues agreed to chronicle their $2.1 million renovation on air, restoring the house to its 19th-century grandeur, rebuilding porches and dormers, adding a music room, an art studio, an open kitchen and two-story windows to the foyer.

The 7,100-square-foot house is now on the market for $9.75 million. One of the selling points: It was rebuilt by Silva of “This Old House.”

Like the other homes featured on the show, the McCue house became a character in its own right, with a story that bound its history to its future. “The house is, in many ways, the most important character on the show,” Vila said.

And if it’s got enough character, it makes for good television.