Their Cape Cod home isn’t small, but its carbon footprint is

When Michael and Jennifer Monteiro bought a home on Cape Cod, they wanted more than just a vacation home near the beach in Massachusetts: they were determined to own something that reflected cutting-edge sustainability.

Since selling the software company he co-founded, Buildium, in 2019, Mr. Monteiro, 51, has used his investment firm, Impactful companies, to focus on projects that address climate change. And his own home provided a clear opportunity to set an example.

As he put it: “Sustainable construction is one of the most important solutions to the climate problem.”

He and Ms. Monteiro, 47, live in Hingham, Mass., outside Boston, with their children, Maddy, 14, and Jack, 12. After buying a second home in 2019 as an escape — an 1980s house on the ocean in the city of Harwich for $2.6 million — Mr. Monteiro started thinking about how he could renovate to make it more energy efficient.

As he looked into it, he discovered a number of problems: the house was poorly built, which made him wonder if it was worth investing in upgrades, and even though it wasn’t in a flood zone, he was concerned about the consequences of rising sea levels. in the future.

“We wanted a house that would last a hundred years or more,” Mr. Monteiro said. “But that’s scary when you think about how the world is changing in the context of climate change.”

The solution, the couple decided, was to demolish the house and start over.

However, demolition brings its own environmental problems. So they started bringing in Green Goat, a non-profit building material reuse organization to save what’s worth saving and recycle as much of the rest as possible. And they hired Estes Twombly & Titrington Architects to design a new structure: a modern, sustainable house disguised as a traditional clapboard cottage.

“Michael possibly mentioned the use of passive house design,” says Adam Titrington, a partner at the firm. “But we certainly didn’t know how deep that interest would ultimately become.”

When they began designing, Mr. Monteiro questioned virtually every conventional building material and proposed method, hoping to reduce associated greenhouse gas emissions while making choices that were good for human health.

Many new homes are tightly insulated with spray foam for energy efficiency, but Mr. Monteiro was wary of the petroleum-based chemicals in those products. So when Kiko Thébaud, a friend who is an architect, told him about hemp-based insulation used in France, he was intrigued.

“It’s called hemp concrete or hemp lime,” Mr. Monteiro said. “It is hemp seed, which comes from the woody part of the hemp plant. You use those small pieces mixed with a lime-based binder and then add water, creating a slurry that can be sprayed into a wall cavity – as we did – or poured into plywood molds.

The walls are finished on the outside with lime plaster; the inside is covered with lime plaster, eliminating the need for wood sheathing, synthetic house wrap, plasterboard and paint.

The only problem? Spraying is the most efficient way to apply the hemp lime, but they could not find an American installer with the necessary expertise and equipment. Their solution was to assemble a team of French, Canadian and American specialists and import the spray installation from France.

But that wasn’t enough: Mr. Monteiro and Mr. Titrington also wanted to reduce greenhouse gas emissions related to the production of other materials used in the home. For the concrete foundation, they specified a custom mix with less Portland cement (which generates carbon dioxide during production) and more fly ash (an industrial byproduct) than would normally be used.

They replaced petroleum-based foam insulation around the foundation with recycled foam glass aggregate. For the sound insulation of some interior walls, they installed HempWool mats. And instead of choosing an exotic hardwood like ipe for the outdoor floors, they used locally harvested black locust.

The house is heated and cooled by electric air source heat pumps, and the solar panels on the roof are designed to generate as much energy as the house uses.

The resulting 6,000-square-foot structure isn’t small, but it does have a small carbon footprint. The habits BEAM estimator of Builders for Climate Action, Mr Titrington found that the house produces less than half the carbon dioxide emissions of a conventionally built building. And in the future it will be largely self-sufficient.

The Monteiros worked with Liz Stiving-Nichols Martha’s Vineyard Interior Design, to furnish the home, by choosing renewable, natural materials – cotton, linen, wool, hemp – and avoiding plastic and synthetics. They worked with local manufacturers and craftsmen to produce much of the furniture, including carpets and sculptures.

The house has a finished basement – ​​currently used for ping pong and shuffleboard – but the walls are removable. That means if flooding becomes a problem in the future, the lower level can be abandoned.

Construction took about two years due to delays caused by the pandemic, but the house was completed in July 2022 at a cost of about $1,200 per square foot. Hoping that others would follow his example, Mr. Monteiro’s investment company helped fund the US Hemp Building Association’s work to get hemp lime approved for residential building codes in the United States.

“I don’t expect everyone to want to build with hemp,” he said. “But I hope it makes people think more about the choices associated with building a house.”

Part of the challenge in finding a more sustainable way to build, he added, is that most people don’t know what’s possible: “As a homeowner, I just didn’t know these possibilities existed.”

Living Small is a biweekly column that explores what it takes to live a simpler, more sustainable or more compact life.

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