Battered by weather and baked by sun, a landing spot for birds and branches, we ask a lot of what lies above. But perhaps we can ask just a bit more of our cottage roofs—to not only keep us dry and protected but also to lighten our overall carbon load as well.
Grow a roof and regulate interior temperature
Ian MacDonald is an architect who spent 20 years in his old cottage on Go Home Bay, Ont., before he tore down the cabin and built a new one. In those two decades, he says, he learned what he appreciated about the location and the space, but more importantly, he saw what he wanted to change. One change he sought was to make the cottage more sustainable. He originally planned to install solar panels, then switched gears to a green roof, which would better control just how hot the cottage became in the summer without relying on AC.
A green roof is essentially a growing roof, alive with organic material. It starts with a rubber membrane, followed by a layer of soil, then the growing material. “Living, green roofs can be very simple and very low maintenance,” says Karen Liu, a green roof specialist with Next Level Stormwater Management in Vancouver. They run the gamut, Liu says, from something people actually go on to enjoy nature, to roofs focussed on adding biodiversity that attract birds and bees. There are even roofs that blend into their surroundings.
MacDonald’s shift in plan to a green roof did require some adjustments. “You would normally have 25 to 35 pounds per square foot of extra capacity to carry a green roof,” MacDonald says. His roof was structured to handle 10 pounds per square foot, “so I went searching for another green roof system.” He settled on a German system called Zero Floor. It required 14 pounds per square foot of support, “a very small deviation,” says MacDonald, and one that fell within the margin of safety required by engineers.
The organic starter material began as mostly sedum, a low-growing, thick-leaved perennial, though it’s shifted over the years, thanks to birds who will occasionally poop out different seeds, which then take root. “The roof has taken on a life of its own,” says MacDonald.
The roof requires little more than occasional watering, which MacDonald does by pumping water from the lake up to the roof using a domestic water system made of standard irrigation piping. He gives it a good 20-minute soak. There is a roughly half-inch drainage layer that shouldn’t get plugged—pine needles are the most frequent culprit—so about once a year, MacDonald goes around the edges of the roof with a leaf blower to make sure it’s all clear.
But although establishing a green roof looks as simple as seeding a lawn, MacDonald encourages people to let the experts handle it. People who try to do it themselves, “can get into really deep trouble,” he says, noting that the membrane technology can be finicky, and installers are typically certified and trained for the job.
MacDonald’s green roof gives him just what he seeks at the lake. “The natural landscape up north is why people go there,” he says. “You want to be in nature—in a building that can allow you to appreciate what is important.”
Meet solar shingles
The past decade has seen an 80 per cent decrease in the cost of solar energy for residential use and a consequent increase in the number of homes and cottages that have installed panels. The next generation of solar technology—which is available but not yet ubiquitous—is photovoltaic (PV) shingles. The roofing material itself acts as a panel.
Katherine Zhou, the co-founder of PV Tech, a Canadian PV shingle company based in Toronto, explains that the shingles, made from an aluminum frame and tempered glass, are like any roofing material and don’t require any additional structural support. They don’t typically cover an entire roof, but rather are located where they maximize the sun’s rays, usually a south-facing slope. An alternate roofing material is used for the remainder. A minimum of a 3/12 slope is required. Anything less than that is considered a flat roof and “this is not designed for flat roofs,” Zhou says. “It would lead water in the wrong direction.” A roof shaded by trees is also not a good candidate, unless you’re willing to cut down or prune any trees that are preventing direct exposure to the sun.
To be “energy independent”—that is, to produce as much energy as you’re using—you would generally need about 500 sq. ft. of PV shingles on a south-facing roof. The roof requires 500 sq. ft. of direct exposure to the sun for the shingles to produce between 7,000 and 8,000 kilowatt hours of electricity a year, which powers the typical home.
For a seasonal cottage, that figure is still a good general rule. The panels are easy to maintain. They can withstand hail and wind, and they’re designed so that snow melts off in the winter; you only need to clear tree branches and debris if they build up.
The advantage of shingles over panels is that if a roof requires replacing, panels need to be removed to access the roof itself (and then you’ll have to pay to have them reinstalled). PV shingles, on the other hand, are warrantied for 25 years, but should last the lifetime of the building, so there’s no reason to remove them.
PV shingles cost more than typical roofing materials—they’re comparable to a metal roof, starting around $16,000—but you can apply for a federal green home grant of $5,000. Ottawa is the first city in Ontario to offer no-interest loans to install PV shingles, but Toronto is rumoured to be following suit.
PV shingles with an Energy Storage System package are particularly attractive to cottagers, says Zhou. “Whenever there is a power outage, a solar shingle roof and energy storage system will power the house for two to four days.”
Make your roof reflect heat
The term “cool roof” refers not to the roofing material, but to a coating or colour that gives any roof a high solar reflectance (SR). The material reflects the sun’s rays as opposed to absorbing them. This reflectance keeps a roof (and therefore the building beneath it) cooler.
But while cool roofs are generating some buzz, they don’t make much sense (or cents) in Canada, where our need to heat year-round homes typically trumps our need to cool them, explains Karen Liu. In cooler climates, cool roofs create what’s called a “heating penalty,” she says. This means any savings the cool roof generates thanks to a reduced need to cool a home during hot months is eclipsed by the increased cost of having to heat that home during cold months.
However, for a summer-only dwelling where cooling is the priority, it’s an affordable option. Cool roofs include light-coloured metal roofs, roofs made of PVC membranes, or even asphalt roofs coated in light-coloured granules (which are not as reflective as the other options but, for the budget conscious, they’re still better than a dark-coloured roof). Or, you can paint a reflective white coating onto your existing roof. (Yep, even onto asphalt shingles—though check that it doesn’t void your warranty.) While white roof paints on the market reflect anywhere from 30 to 60 per cent of solar rays, researchers at Purdue University in Indiana have developed a barium sulfate-based paint that reflects 98.1 per cent of rays.
This article was originally published in the August 2022 issue of Cottage Life.