A green roof is so much more than a roof garden, I discovered in Scarborough. It’s a living roof that’s attractive, insulates and benefits the environment.
Tom Gray has been building these living roofs for many years and believes they are the roofs of the future.
The first green roof we visit in Scarborough belongs to Cindy and Richard Hartley and is best viewed from a deck overlooking it.
It’s a succulent garden, about 40m2 and sits at a slight angle for better drainage. From the deck you look across the planted roof to the reserve and the sea, and instead of seeing a roof, your view is of vegetation.
While aesthetic considerations are one of the reasons for a green roof, there are a lot more. Insulation is one, creating new green spaces another. There is a lot of insect life buzzing around this garden.
Gray grew up around plants at his parents’ Good Hope Nursery near Cape Point and has always loved fynbos. After training as a carpenter, he moved into the nursery business and started his own landscaping business, Good Hope Gardens.
“I became interested in the architectural aspect of the roof garden, the aesthetics, but also its insulation properties. The growing roof keeps the room below it cool in summer and warm in winter.”
With climate change, it’s the roof of the future, especially in densely built urban areas.
“I researched the field, but there was little information available, and so started experimenting with different materials.”
A dog’s kennel was the first experiment. Drainage is all important. This garden has a gravel pit around it, no gutters, which filters the water.
“The big thing is to have drainage layers, and there are a number of products on the market.”
Through lots of trial and error, Gray has found materials that work well.
“There are many ways to do it, but if you’re working on a large scale, it makes sense to buy the material – it saves time.”
It’s important to start with a 100 percent waterproof roof.
Each green roof is designed taking into consideration many factors, such as situation, depth of soil, the homeowner’s preferences.
It also depends on the building – if its design requires lightweight structures that limits the depth of soil, and in turn which plants can be planted there.
“The depth varies between 120mm to 200mm soil,” says Gray.
However, one of his gardens in Fish Hoek has deeper soil, and can be planted with vegetables.
Wind is a factor to consider on green roof gardens, as it can blow many times harder on the roof than on the ground.
Succulents, especially those endemic to the Western Cape, are ideally suited to these green roof gardens. Gray likes using Portulacaria afra or repens, also known as Elephant’s food or spekboom.
They are also carbon sink plants – they bind atmospheric carbon that is responsible for climate change.
The roof needs regular maintenance.
“Initially, I plant long- and short-term plants. This garden is around six years old, and some plants need replacing.”
It also needs watering.
“With this depth of soil, you need to irrigate in the heat of summer. Although it does hold some moisture, it also dries out in the extreme heat.”
Botanist Nick Helme’s green roof garden, also in Scarborough, seldom gets watered and when it does, it is with a sprinkle from his hosepipe. His garden is built on top of his office, a timber-frame structure.
The roof was at the level of his deck, he says, and he didn’t want to look straight onto a glistening roof.
So they created a green roof.
With his extensive knowledge of plants, Helme was very involved in plant choice. His garden is about 18 months old, and he’s limited plants to those of the Western Cape, which includes the Little Karoo.
“I don’t want arid succulents, though, not in a high winter rainfall area.”
He has about 60 species growing here, a few of them rare plants.
It’s not the best time of year for the garden, he points out, with few plants flowering now – May to December is best. But the garden is interesting. Succulents come in so many shapes and colours. He’s planted many bulbs, but the only problem with these is that the baboons like them.
Maintenance means a hop over the railing onto the roof to weed.
“As a botanist, I’m obsessed with aliens and the first spring season I weeded them out as I saw them.”
Drainage is excellent, and slow. After a deluge, the water begins to drain only after 20 minutes, and then drips slowly off the edge for a few hours.
Green roof gardens are growing in popularity, slowly, as one way to mitigate pollution in cities. They’re a way to increase green spaces in built environments; there’s no need to repaint your roof or clean your gutters, and the drainage acts as a filter for “acid” rain, so what runs out the outlet pipes is clean. And they’re natural insulators against heat and cold.
“Everyone should have one, it’s a no-brainer really,” says Gray. - Cape Argus