“They are unique in the way that they undulate,” Mr. Reidy said. “Most doors don’t do that.”

But by 2017, few of them were operable, and the single-paned glass made the house drafty and cold. They needed to be updated, but the homeowners did not want to sacrifice character for comfort.

“That’s the whole reason for the house — it’s those windows,” Mr. Barnes said.

But after spending a summer there, they decided they did not need to be quite so open to the outdoors, as New England summers are hot and buggy. And with so many doors, guests often didn’t know which was the main entrance.

So the couple decided to replace the undulating French doors with a wall of fixed glass doors, with only one opening to the front. They created a more formal entryway by renovating the mudroom, installing insulation, a proper foundation and a wooden front door, painted black.

Replacing the original French doors, which had likely been built on site, with similar ones wasn’t an option: The homeowners wanted as much glass as possible, and wood frames tend to be wider.

They decided on steel, which would be strong, maximizing the area of glass and giving the house the minimalist aesthetic they wanted. But it wasn’t cheap. Fitting the entire house with steel-framed windows and glass doors would cost $160,000, a price that came as a shock.

“We were surprised at everything,” Mr. Barnes said. “Why are windows so much money?”

The architects suggested an alternative: aluminum, for half the price. But aluminum isn’t as strong as steel, so most of their options had thicker frames, cutting down on the size of the glass. Finally, they found a manufacturer in upstate New York that made aluminum windows with thin frames, but the double-paned glass had to be ordered from a different company.

The look, while close to the couple’s vision, was not exactly what they had in mind. “We love them, and it looks amazing,” Mr. Barnes said, but with steel, “it could have looked more amazing.”