There are secrets to greening Halifax in the coastal barrens
of Peggys Cove.
Scott MacIvor is conducting groundbreaking research there as part of
his master’s degree in applied science at Saint Mary’s University: “I’m
studying the plants.”
MacIvor notes that coastal barrens plants live in similar conditions
to those you might find on a Halifax rooftop. “There are high winds,
they are exposed to sun and drought and they are regionally specific,
accustomed to our climate,” MacIvor says. He and his supervisor sought
local plants that survive in harsh conditions in the hope of
revolutionizing Halifax rooftops.
A green, or living, roof is a plant-based extension up from an
existing roof. It requires extensive waterproofing and protection from
root growth, a drainage system and relatively lightweight plants.
“I’m passionate about green roofs because I’ve always lived in urban
environments,” MacIvor says. “We have a lot of impervious surfaces,
roads and buildings, which don’t allow water through.”
Concrete and asphalt create storm-water runoff, one of the reasons
Halifax Harbour is polluted. These hard surfaces also trap the heat of
the sun, creating the “urban heat island effect,” whereby cities tend
to be a few degrees hotter than surrounding greener pastures.
MacIvor lists the many benefits green roofs provide: “They counter
the urban heat island effect and mitigate carbon dioxide and other air
pollutants; increase biodiversity; provide refuge for valuable urban
wildlife including carnivorous insects for pest control; allow for
storm-water retention; provide cooling, insulation and energy savings
and they protect the roof membrane so the roof lasts longer.” Green
roofs also increase sound insulation and fire resistance, improve
general health and reduce stress.
The environmental and health benefits of green roofs have been
documented as far back as the hanging gardens of ancient Syria and in
Western European nations such as Germany and France they blossomed into
a multimillion-dollar industry in the early ’90s. We’ve been slower on
the uptake in North America, where the benefits are poorly understood.
According to MacIvor, we have the potential.
“I see increasing growth across North America,” he says. A few years
ago, a survey of green roofs in Halifax turned up more than 50
examples, atop institutional buildings and personal residences. MacIvor
notes a few recent highlights, including a green roof at Citadel High
and a second, bigger green roof being installed at SMU. He says that
with an increasing understanding of locally appropriate plant
technology, the number of green roofs in town could explode.
“Green roofs in North American conditions are not well researched,”
says MacIvor. “And you have to do it city by city; you can’t copy what
we know from Toronto in Halifax.” The climates are too different. Most
of the world’s research on green-roof technology comes from Germany,
which means that we may not be using the best available plants for our
climate.
MacIvor’s research, conducted out of SMU’s Green Roof Testing
Facility, aims to enhance our green-roof plant selection and bolster
efforts to green Halifax’s skyline. The data will be used to create
“habitat templates,” plans for real living rooftops.
If these hardy flora prove effective, Halifax may be the perfect
milieu for a green- roof renaissance because of our low density and
relatively flat cityscape. According to a recent paper from the
American Institute of Biological Sciences, “Green roofs will have the
greatest effect on energy consumption for buildings with relatively
high roof-to-wall-area ratios.” In other words, low-rises.
Green roofs offer the greatest energy savings for homeowners, who
may eventually benefit from another advantage of coastal barrens
plants: “They can grow in only two inches of soil,” says MacIvor. This
saves money and reduces weight, a factor in making green roofs workable
on smaller structures.
Aside from the lack of local research, cost is the biggest reason
green roofs have yet to flourish on your street. Costs vary widely
depending on a roof’s size, type and angle, but generally fall between
$10 and $20 per square foot. It’s a serious investment for something
that could cause its progressive new owner a winter of suffering over
die back—when the plants go dormant.
For that reason, many “green” builders prefer to stick with
tried-and-true solar panels, but MacIvor resists the
garden-versus-solar-panel debate. “Solar panels can be used in
combination with green roofs,” he says. “But green roofs offer benefits
to the environment beyond thermal benefits, like absorbing storm
water.” Green roofs also save money long-term due to energy savings and
increased longevity of roof membranes.
Overseeing the economic and the scientific is the political. In
European states with large green-roof industries, inevitably you find
legislated green-roof requirements written into building codes. So far,
Halifax has talked good sustainability talk, but regulated little other
than building heights and planning processes.
Do you have a green roof? Drop Chris Benjamin a line
at chrisb@thecoast.ca.
This article appears in Jan 8-14, 2009.