Green Roofs in Winter

Photo: A green roof in Victoria, BC
We know green roofs reduce cooling bills in the summer—but what about winter?

When you think green roofs, do you think summertime savings? Lower cooling costs are generally what people associate with green roofs, but did you know that the insulating qualities of green roofs are also great for winter homes? It’s true: adding a green roof to your green house plans—whether you live in a single family home or a multi-family dwelling—will likely have a positive impact on your heating bills.

A study done at the University of Toronto analyzed a test roof built in Ottawa that offered the first ever study into whether a green roof could improve the efficiency of the home in winter. Using two winter green roof models (consisting primarily of Juniper shrubs), and contrasting them against a conventional asphalt roof, simulations were tested in January and February. Though the vegetation reduced the conservation of heat by shading the roof, the scientists found that the green roof would increase conservation of heat by reducing wind speeds and modifying the microclimate above the roof.

We know that green roofs can reduce cooling bills by up to 75 percent compared to conventional roofing, but here’s what the scientists found out about green roofs in the winter:

  • A home built with asphalt roofing required on average 7,748 kWh of heating energy compared to only 7,287 kWh of heating energy for the test home with a winter green roof.
  • The potential heating energy savings were estimated to be between 5.63 percent and 5.95 percent, with savings up to 61 percent for upper-level floors.

Green Roof Diagram Green Home Plans

There are many types of green roofs—those made with shallow soil bases and low-growing plants for sloped roofs and those with deep soil bases with tall trees, vegetable gardens, and more, to name a few—so the winter benefits of a green roof would greatly depend on its design. But the study was a huge factor in getting the City of Toronto on board with green roofs—they developed a Green Roofs for Healthy Cities initiative that has fantastic benefits for the city.

There are many more advantages to having a green roof on your home—too many to go into today—making it a feature you should definitely consider when making your green house plans.

 

YellowBlue DesignsYellowBlue Designs sells green house plans and blogs about ways to green your home.