EASTHAM — Martin and Ellen Ridge plan to demolish a 976-square-foot cottage that sits on one acre at 150 Crosby Village Road overlooking Herring Pond. They want to replace it with a 4,000-square-foot one-story house with an attached breezeway and garage.

That progression — from modest cottage to sizable residence — has become commonplace on the Outer Cape. What’s unusual in this case is the way the Ridges’ proposal has sailed through the permitting process over the last few weeks.

Water is an important reason that happened: the plans include shifting the house outside the 50-foot wetlands buffer zone around the pond and marsh and installing an alternative septic system — part of a pilot program being overseen by Barnstable County — to remove nitrates and phosphates from wastewater. The cottage now on the property sits almost completely inside the buffer zone.

The Ridges, who moved from Boston to their house at 5 Ben’s Way in Eastham after retiring 10 years ago, bought the cottage on Herring Pond in 2014.

Because the cottage dates to 1938, it enjoys some protection under the town’s demolition delay bylaw if it is judged by the historical commission to be either historically or architecturally significant. At a Nov. 15 hearing, architect Alison Alessi told the commission that two bedrooms were added in the 1950s. The cottage had no distinctive architectural features worth preserving, she said.

The Ridges had made some improvements on the cottage and considered expanding it to make it their primary home, Alessi said, but that did not prove feasible. “It’s just not structurally viable,” she said.

The structural deficiencies include termite damage to the joists, water infiltration where the original cottage and bedroom extension meet, and a wet basement due to cracks in the foundation.

Commission Chair J. Holden Camp Jr. had toured the cottage and said he observed serious water and insect damage.

“The cottage has low ceilings, and some doorways are only six feet tall,” said Martin Ridge, adding that he has to remember to duck because he is over six feet tall. Ridge is a retired electrical engineer as well as a furniture maker and woodworker. He told the commission he plans to repurpose what he can — particularly wood floors and kitchen cabinets — from the cottage.

At the end of the hearing, the commission unanimously approved the request to demolish the cottage.

On Nov. 16, the Ridges went before the planning board for its site plan review and approval. It was smooth sailing there, too.

The new house will have a modern design with a gray metal roof and cedar-shingled exterior meant to blend into the lot. Alessi said the house will be built to resemble three small cottages. And its mass will be further hidden because the house will be built into the sloping lot so that the first level will be five feet below the grade of the street, she said.

The only neighbor to express concern during the planning board’s hearing was Christopher Puff, who lives across the street from where the cottage now sits. “Obviously it’s a big change for us,” he said. But even though the small cottage will be replaced with a large house, Puff conceded, “it looks like it will fit in well.”

While the new house will be just under 30 feet high at the peak of the gables, other areas will be lower, Ridge said, assuring Puff he will still have a view of the pond.

When Puff expressed concern about the removal of trees, Martin Ridge said 22 trees were set to be taken down but they were mostly scrub pines. A large oak tree on the property will serve as “the cornerstone of the landscape plan,” Ridge said.

The Ridges had met with neighborhood residents to explain their project. The planning board received three letters of support and none in opposition.

Planning board member Craig Nightingale called the proposal “one of our better projects.” Member Rob Young took in the view from the water while kayaking. “I was pleased,” he said. And board clerk James Kiviehan agreed. “I really like the project,” he said. “I’m totally on board.”

With that, the planning board unanimously approved the site plan.