green roofs

Urban greenery in Vancouver

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A green roof on top of a skyscraper, as seen from the Granville bridge
A green roof on top of a skyscraper, as seen from the Granville bridge

Last week I was in Vancouver (Canada) for work, and in amongst the conference and meetings I had a chance to walk through most areas of the city.

It’s a lovely city. It’s also interesting to see little patches of greenery popping up in unlikely spots.

This includes a green roof on top of a skyscraper (above), and community gardens squeezed into unused spaces (below). There were also a few rain gardens, which looked to have been installed as part of the preparation for the Winter Olympics, which were held here a few years back.

Say what you like about top-down policies and strategies for addressing climate change. Even in the absence of these, cities around the world are undergoing a quiet revolution that is connecting people to communities, food and the environment.

Community garden alongside disused railway tracks, south of the CBD.
Community garden alongside disused railway tracks, south of the CBD.
Community garden, right in the heart of the city.
Community garden, right in the heart of the city.
Greening a roundabout: "This street garden is being cared for by a local resident involved in the Green Streets Program."
Greening a roundabout: “This street garden is being cared for by a local resident involved in the Green Streets Program.”
Rain garden, near Vancouver's stadiums.
Rain garden, near Vancouver’s stadiums.
Large scale urban agriculture, right at the foot of the huge stadium.
Large scale urban agriculture, right at the foot of the huge stadium.

A possum ate our green roof

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This plant got off lightly, some of the rest are just stalks!
This plant got off lightly, some of the rest are just stalks!

A bit over a week ago, I finished and planted out our small green roof, placed over the end of the chicken run.

This weekend just passed, I went out to check how it was going … to discover that a possum had eaten a fair bit of the green roof.

The tough plants, such as the lomandra, dianella and thicker ferms were OK. The ground covers, including the native violet, had suffered hugely. As had the more delicate ferns.

This isn’t a new problem for us, and some of our young trees are surrounded by wire mesh, to protect them from a hungry local possum.

In the short term, I’ve protected the plants with wire. In the longer term, I may have to switch to tougher, less tasty plants.

Ah, the perils of living systems!

Is this Sydney’s smallest green roof?

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The small green roof, fully installed and planted on the end of the chicken run.
The small green roof, fully installed and planted on the end of the chicken run.

A green roof is where a garden is installed to cover a roof, typically to a depth of 150mm on top of a strong waterproofing layer. It’s a great way of getting extra greenery into a property, and the roof also asborbs water run-off.

About a month ago I stumbled across the book Small Green Roofs, on Amazon. It’s a wonderful book that has 40 different inspiring case studies, all covering small, non-commercial green roofs (full book review to come).

Feeling inspired (and running short of projects around the house), I decided to construct a green roof at the end of the chicken run.

At 1.2m x 1.6m (1.9m2), this may be Sydney’s smallest green roof.

The corrugated iron that previously covered the end of the chicken run.
The corrugated iron that previously covered the end of the chicken run.

When we created the chicken run, I installed several left-over sheets of Colorbond at the end of the chicken run, to give cover for the chicken feeder (and the chickens!). This is now replaced by the green roof.

The structural ply installed, along with extra structural support.
The structural ply installed, along with extra structural support.

The starting point was to install a sheet of 25mm exterior-grade structural ply. This is very strong (and heavy), and it provides the base for the green roof.

The next challenge is to deal with the extra weight of the green roof. For a soil depth of 150mm, a green roof weighs 250kg per sq. m. That’s a lot!

Thankfully the chicken run was constructed strongly in the first place. To provide extra support, I installed a new vertical post (front left corner of the new green roof in the picture above). This was concreted into the ground. Extra rafters were installed, along with bracing back to existing posts.

Other than the structural ply, everything else used wood and materials salvaged locally, or left over from the house renovation.

The sides of the green roof go on.
The sides of the green roof go on.

The sides of the green roof were constructed out of left-over roof beams, 200mm high. Because the sides of the wood were very uneven (from sitting in the weather for 10+ years), I put in an extra layer of ply to assist with waterproofing.

There’s a 20mm gap along the bottom edge of the green roof, to allow water to drain away.

The waterproofing complete, ready for the garden itself.
The waterproofing complete, ready for the garden itself.

I had some left-over “pond liner” paint, so I used three coats of that to seal the base and sides of the green roof. On top of that I installed a layer of 20mm Atlantis flo-cell (left over from the reworked raised garden beds). A layer of geotextile then keeps the soil out of the drainage system.

The green roof planted out.
The green roof planted out.

As a stroke of luck, just as I was ready to fill the garden bed, a friend rang to ask whether I needed any soil, as he was clearing out his back garden. A ute load’s worth of soil later (courtesy of GoGet), this is the final green roof.

Green roofs would typically be planted with sedum (a low growing succulent), to cope with the extreme conditions and low water levels. In this shaded position, however, that isn’t an option.

Instead, I’ve put in some water crystals, and have planted out the garden with a mix of:

  • lomandra
  • dianella
  • ferns
  • native ground covers (native violet, white root and northern cranesbill)

Already it looks great from the back verandah, and I’ll blog new pictures in six months after (hopefully) the plants have all grown up.