Woman from Cambridge turns garage roof into green oasis

DIYer

Living roofs are valued for their environmental and financial benefits. Commonplace in Germany, they are slowly spreading among Americans.

By Megan Johnson, The Boston Globe

December 4, 2024

When her two children were young, Barb Bryant wanted to get them interested in gardening. She couldn't have cared less, but the venture was an inspiration. In 2023, Bryant transformed the roof of her Cambridgeport garage into a 1,200-square-foot green roof, complete with perennials, vegetable plants, and an apple tree.

“The years went by and we kept dreaming about this garden on the garage roof and then decided to make it a reality,” said Bryant, a computational biologist who also runs a nonprofit called Navigation Games. Her partner Dave Yee works at Novartis.

Bryant and Yee weren't alone in their dream of turning the garage into a green roof, a layer of vegetation grown on the roof. Green roofs, also known as “living roofs”, are widespread in Germany and valued for their ecological and financial benefits. But on this side of the pond, the practice has barely scratched the surface.

Bryant turned to Recover Green Roofs, which designed and built rooftop farms at Fenway Park and Boston Medical Center. The first step was to ensure that the garage was structurally sound enough. The garage, which spanned her and the neighbor's property, did not entirely belong to Bryant, who negotiated an agreement with the neighbors in which she would pay for the reconstruction of the garage, which would be necessary to support the weight of the roof terrace and garden to wear . In return, they would allow her to garden on their side of the new rooftop patio for the next 10 years. Next, she had to get approval from the city of Cambridge and the zoning board, which wanted to make sure the rooftop deck didn't become a party space. She finally received approval.

Today, a staircase leads from Bryant's driveway up to the green roof, and there is also a flight path that leads from the second floor of the house to the garage roof. There you will find a corner of the garden full of sedum, grasses and a variety of other small perennials. There is an apple tree and a few peach and pear trees. The rest is filled with food plants and flowers so the family can grow their food. A picnic table provides additional living space and essentially increases the square footage of the home.

“We really enjoy being able to produce our own food,” Bryant said.

Drive along Route 1A in Revere and you'll spot a 6,000-square-foot residential rooftop, reportedly the largest and steepest at a residential project in New England, in Gibson Point, a new 291-unit condominium community. It runs diagonally to be clearly visible from the ground. It is filled with 15 to 16 species of sedum and will fill with pink, yellow and white flowers in the spring.

From an ecological perspective, the benefits are significant. At Gibson Point, the floor of the living roof serves as an insulator. It absorbs rainwater and moderates the water flowing downward during stronger storms. When sunlight hits the diagonal slope, the building's energy costs decrease and water vapor is released back into the sky.

“I think this fits well with the concept of regenerative design, the principle of leaving the site in a better place than where it started,” said Amy Korte, president of Arrowstreet, the architect behind Gibson Point. “You think beyond just designing for the people in the space and also think about the climate and living spaces you can create.”

According to the U.S. General Services Administration, temperatures on green roofs can be 30 to 40 degrees lower than traditional roofs and can reduce ambient temperatures across the city by up to 5 degrees. Green roofs provide shade and rainwater management and reduce heat islands.

“A green roof is a beautiful antidote to cooling our cities without using electricity,” said Mark Winterer, owner and co-founder of Recover Green Roofs.

But of course the question arises: How much does a green roof cost? Winterer said the costs were “huge.”

Installation costs depend on “the size, depth, plant types and height on a roof,” Winterer said, noting that a smaller residential green roof would cost $55 to $75 per square foot, but prices drop larger is it.

“The size, depth and how we access the roof will impact the price,” Recover said in an email to the Globe. “We installed a lightweight green roof on a garage in Lexington last year that we were able to pull our trucks into from the driveway, making access very easy without heavy equipment. That covered half of a 1,200 square foot garage roof and cost $35 per square foot. If this customer had covered his entire roof (he had a patio on the other side), it would have cost $25 per square foot.” This does not include the cost of supporting the roof to handle the garden weight and snow load.

“We work with structural engineers on all of our projects and design our systems within the buildings’ available loading capacity,” Recover wrote. “Most roofs built in the last 70 years were built solely to support the region's snow load, and these customers need to add reinforcements to support a heavier green roof system, similar to Barb's.” She actually has demolished their old garage and built a new one with the necessary reinforcements. We also have some ultra-lightweight green roof options that may be within the available load capacity of an existing building and that we have used successfully in retrofit projects without the need to add reinforcements.”

There may be financial benefits after installation, but there are many factors. Green roofs help cool a building, reducing air conditioning costs while electric bills skyrocket for Boston area residents. Lawrence Berkeley National Laboratory researchers who conducted a cost analysis found that while green roofs are more expensive than traditional roofs, they provide significantly higher relative benefits per square foot over a 50-year life cycle due to energy cost savings, avoided emissions and reduced stormwater fees, explained the Environmental Protection Agency.

“A green roof is a nice antidote to cooling our cities without using electricity.”

MARK WINTERER, co-founder of Recover Green Roofs

To keep costs down, Recover often uses low-maintenance facilities that require two to eight visits per year. However, rooftop farms that produce vegetables may require two visits per week. What do these visits include? They include hand weeding, cleaning drains, removing debris, soil testing, organic, low-dose fertilization as needed, biological pest control, organic farming and harvesting of vegetables, pruning, removal of dead plant debris, replanting of dead plants, and irrigation maintenance . “Our lowest cost contract is a small local customer in Somerville. We only start irrigation in the spring and turn it off in the winter, which costs $250 per visit ($500 total). The homeowner will handle all yard work and cleanup,” Recover said via email. “The other residential customers cost up to $1,000 per visit and are somewhere in between depending on the roof size, planting type, time of year, number of people needed and how we move materials up and down the roof can.”

In New England, where the climate is anything but predictable, green roofs generally grow perennials that go dormant in the winter. However, some may contain evergreen plants of winter interest.

Bryant, Yee and their neighbors love having a green space to look at instead of a black membrane roof. Occasionally passers-by see her working in the garden and she invites them to take a look and send them home with a bouquet of flowers or herbs. Her favorite moments are when children come over and follow the journey of growing food.

Bryant also feels like the green roof increases the square footage of her home, but overall it just makes her smile.

“From a personal satisfaction perspective, just looking at it and gardening there makes me happy,” Bryant said. “The hustle and bustle of the gardener, that things happen a little differently every day.”

Follow Megan Johnson on X @megansarahj and contact @globehomes.