We have been hearing a lot about green roofs lately, but mostly in the context of large commercial projects such as the new visitor centre at VanDusen Botanical Gardens and the waterfront Vancouver Convention Centre, with its impressive six acres of living roof.
It might even surprise you to learn that when you are shopping at the Canadian Tire or Wal-Mart just over the bridge in Port Coquitlam, you are also pushing your cart under some of the largest green roofs in the Fraser Valley, with the one on Wal-Mart occupying more space than two NFL football fields.
I have to admit that the current green roof trend really hasn’t trickled down to the average consumer, as I only know of a handful of gardeners who have tried small scale green roofs on their cottages or garden sheds.
So when I got an invite to an upcoming residential green roof installation from fellow horticulturist Kelly Koome of Green Earth Landscaping, I jumped at the opportunity.
Although I have had some experience installing large-scale roof-top gardens from my landscape days, this was before green roof technology had arrived here from Europe, so we were essentially creating traditional landscape beds on multi-storey buildings – with soil weight, drainage, root systems, plant hardiness and irrigation being our primary concerns.
Still, gardeners have been trying to put plants on their roofs for centuries, beginning with the hanging gardens of Babylon, built by King Nebuchadnezzar the Second for his wife in the 7th Century BC.
On a more practical scale, sod roofs (stripped from nearby meadows) were once common in Scandinavia and much prized for their insulating value – these would eventually find their way to the Canadian prairies with some of our first immigrants.
Today’s green roofs are carefully engineered products with modular growing trays, precisely blended growing media (with only seven to eight per cent organic matter) and specially selected plant species chosen for their hardiness, durability and shallow root systems.
The green roof installation I was viewing with Kelly was the Calvert residence in Coquitlam, a recently built home with a definite West Coast feel to it. The flat roof they had chosen to cover was a 20-by-30-foot area overlooked by a small patio and a room with nearly floor to ceiling south facing windows – so they would have a perfect view of their new garden.
They chose the LiveRoof hybrid green roof system, which is provided by NATS Nursery of Langley. The trays were custom-grown for the Calverts and they were actually able to choose which species they wanted, settling on a blend of several evergreen and herbaceous Sedum or Stonecrop – these were started back in April and they were given regular updates from the nursery.
By the time I arrived, the existing area (with a standard two-ply roofing pigment) was already prepped with a layer of 10 millilitre plastic and drainage mats, carefully configured around the drains.
The finished LiveRoof modules and edging materials were crane-dropped directly onto to the roof in specially designed Hoppit racks. The installation (which must be conducted by trained installers and, in this case, the Calvert’s son) is relatively easy, starting with the placement of the Permaloc edging system, after which the trays are simply placed in sequence, the soil elevators removed (this allows for soil contact between trays), then the finished green roof is simply watered to allow any loose soil to settle.
Mike Lascelle is a local nursery manager and gardening author (hebe_acer@hotmail.com).