As the 20th anniversary of Rouge approached, owner Rob Wasserman took stock: The bistro, which ushered in the city’s era of sidewalk dining, was busy enough but — like any restaurant — feeling the pressure of competition.

Although Rouge occupies a prime perch on 18th Street across from Rittenhouse Square, it’s always faced two intractable obstacles: Most seating is outside and weather-dependent, and the interior itself is tiny — only 750 square feet, dominated by a circular bar.

Wasserman called Meg Rodgers, who designed the restaurant for his father-in-law, Neil Stein.

The results, presented this week after a 10-week renovation, are impressive:

It feels like Rouge, but with about 50 percent more seating. And yet it doesn’t feel cramped.

By repositioning the bar to the rear wall under the existing chandelier, Rodgers managed to add 22 seats to the 40-seat dining room. The new bar, which has the same scalloped Corian top that Rodgers installed for the 1998 opening, is slightly larger but is square. Overall, it is less a focal point of the room.

A releveling of the floor allows better views of the square from the rear. Banquette seating along the walls will allow for larger parties. Drapery on walls has given way to paneling and upholstering. Soundproofing has been added. Sidewalk tables and chairs are new.

Rouge also has a new chef, Sean McPaul (ex-Tangerine, Talula’s Garden, High Street on Hudson), whose all-day menu retains only the signature 12-ounce, Gruyère-topped burger. The new menu is built primarily on smaller plates, such as duck wings, seared scallops, and cauliflower croquettes. Only three larger plates are on the initial menu: a half-chicken, black bass, and filet mignon.

Wasserman also retained the cocktail services of Hop Sing Laundromat owner Lê to design the drink menu.

Rouge, occupying a shuttered liquor store in the Rittenhouse Claridge, is the last surviving restaurant of Stein, who died in October at 77. In the early 2000s, after a three-decade run of projects, including Marabella’s, Rock Lobster, Fishmarket, and Striped Bass, he found himself in extensive financial and legal problems, and in 2006, his daughter and son-in-law, Maggie and Rob Wasserman, bought out the previous partnership and assumed control.

Rodgers, who more recently designed such restaurants as Panorama, Royal Boucherie, Nineteen (XIX), and High Street on Hudson, talked with us recently. She said Stein had bold ideas but did not always articulate them conventionally.

What was Neil going for?

He definitely wanted it to be a sexy bar. Neil always would tell me how he wanted places to feel. He wouldn’t be able to describe the look always; you know, he would use adjectives. Sexy, intimate, cozy. He wanted it to be really an all-day dining experience, that people could have brunch, lunch, dinner. It was a neighborhood place. He wanted it to appeal to a lot of people. I’m sure I have notes in files of all of his adjectives — I was supposed to write them all down. What I remember the most was sexy, intimate, hot, cozy. A bar scene, but sophisticated. … I do remember being very proud of it. I thought there was really nothing like it in Philadelphia, especially the outdoor cafe. That was the real groundbreaking move on his part.

Did you ever think to yourself over the years that, hmm, maybe the room could have used this?

I think Rouge was pretty tight. I felt over the past several recent years that it was worn down. … I always thought the bathroom needed to get dressed up. We’ve done that now, adding wallpaper and really made it fun.

What were the initial conversations with Rob Wasserman like?

We kept doing different plans at the bar and Rob was just very torn. He wanted more seats but wanted to keep it Rouge. I was there and my best friend met me there, and she hasn’t been in Rouge in a while and she goes, ‘What’s new? It kind of looks the same. Remind me what did you do?’ I thought that was great.

Tell me about the changes.

We really wanted that kind of jog of a memory where somebody could go, ‘Oh, my God. Is this the same bar?’ That’s OK. It’s almost like preserving something from the past. We didn’t want to completely alter it, but really dress it up. I think what we were referencing this time were these wonderful hotel bars mostly in London, like the Connaught and Churchill’s.

There’s no more drapery; the walls are upholstered. We did acoustical panels behind them and then upholstered them. It’s got actually really nice acoustics. We did an acoustical panel in the ceiling, in the oval. I felt that, with this bar, I felt like Rouge was growing up and becoming a little more sophisticated, and, you know, we needed to also soften it. Give it a little notch up. Then we have drapes just in the back, in front of the service station, to just kind of make that go away.

The mirrors remain, but we rehung them on cord and tassels. The chandelier remains, and the sconces. The chairs are the same, and we reproduced the bar stools. It’s a new bar, but we kept the edge.

Was there any thought of doing something more radical?

That would have been a mistake. It’s such a classic spot. It needed to be soft, sexy, and intimate. It needed to be all these things that Neil had always wanted it to be.

What would Neil think?

He would think it’s really intimate and romantic, and it’s a great bar — a place to go sit and drink and eat. It still really embraces the park, so you’re really still feeling like you’re a part of that experience. I think he would like the fact that that original design, designed really 21 years ago, was such a classic that it beat the test of time.