Imagine our cities with birds and butterflies flitting from building to building. Imagine views from tall buildings that include roof tops full of plants, rich with life and colour and the sound of birdsong and insects. This is starting to happening all over the planet. People are seeking alternatives to the alienating and sterile world of concrete, without moving to the countryside. Roof gardens provide all of this and much, much more!
I have dreamed of creating my own green roof for so long it hardly seems real that it is now in. This post is about the benefits of green roofs and quite a detailed ‘How To’ guide for those who wish to do the same. Early inspiration came from the Green Roof Pilot Project (GRPP) at eThekwini which is testing various options that provide healthier urban environments. This project among others has shown that these living roofs (as they are also called) naturally increase biodiversity and are aesthetically beautiful, but there are numerous other good reasons to seriously consider installing one:
- They insulate the house, reducing the amount of cooling and heating required
- They lower the amount of storm water run-off
- Improve air quality through the reduction of air borne pollutants, including harmful carbon monoxide.
- They absorb chemicals and heavy metals from rainwater
- There are positive climate change impacts via absorption of carbon dioxide and the release of oxygen during photosynthesis.
- They help insulate for sound
- They reduce maintenance cost of roofs and increase its lifespan by two to three times.
- Can assist in the alleviation of food security issues.
- Provide fire resistance
- Offer electromagnetic insulation.
There are broadly two options for installation. One way to go is planting in trays. I have used the direct method which involves placing the shallow amount of growing medium on top of various protective and drainage layers which I will show step by step.
Before you start though it is imperative to ensure a structural engineer has confirmed that your roof can take the extra load (or if you are building from scratch engineer into the design).
We began by installing a serious waterproofing product called ExtruBit ® . This stuff looks a bit like wet suit material is flexible and really tough. A company called Bertrade did the installation which involved heat sealing the overlap areas. No mean feat in Durban’s hot and humid February.
The next three layers provide the drainage and help ensure the soil won’t get into the full bores. Pula Water supplied their amazing drainage mats (Flow-Cell ®) which are sandwiched by geotextile. This was a cinch to install, somewhat reminiscent of playing with Lego as you are rewarded with a very satisfying click as each mat slots into the other! In addition to ensuring the water will drain
away they are designed to do so slowly so plants have time to drink.
You are now ready for your soil mix. My soil has come out of the ground being dug for the water harvesting tank. Not very nutritious so I have mixed it half/half with pine bark compost from Grovida.
In addition I have added bags of organic accelerator, agricultural lime and 2:3:2. Over and above general dispersal of the above, each largish plant hole received a handful of the extras to give a nutritional boost.Before we talk the about the most exciting bit which is obviously the plants I have to share with you the less interesting but vitally important info on how to deal with your full bores. This is the area you roof garden will ‘fall’ to (i.e. slope down to) and it is crucial that you have sufficient drainage or your garden will fill up and swim over the edge of it. To help slow down the process in the event of heavy rain this is what you can do:
Choose your plant species carefully. It goes without saying your locally indigenous/native plants must be selected and these should be water wise and heat tolerant. Plants that grow in cracks and crevices are ideal. Bear in mind that the soil is shallow and will dry out quickly. Plants should (in the main) also be low growing and wind resistant. Ideally they should also be self seeding to replace themselves when stressed by heat and water fluctuations.
They beauty of using the correct plants means that after they have been established irrigation is seldom required. Plan to utilize at least one of the many water harvesting options. Gutters and grey water re-cycling are easily installed. (Detailed posts to follow).
For those of you in Durban South Africa here is a list of plants that will do well:
|Aellanthus parvifolius, Aptenia cordifolia, Aloe maculata, Aloe cooperii, Bulbine abyssinica, Bulbine natalensis, Cissus quadrangularis, Cissus fragilis, Crassula multicava,
||Crassula hirta, Crassula ovata, Crassula obovata, Crassula perofliat, Crassula vaginata, Aloe rborescens, Aloe rupestris, Aloe thraskii, Aloe van belanii, Cotyledon orbiculata,Delosperma rogers|| Hibisucs calphyllus, Kalanchoe thyrsiflora, Nymphoides thunbergiana, Portulacarai afra, Stafpelia ginantea, Vernonia capensis
I know this garden will give us much joy in the years to come. I hope you’ve been inspired!
P.S. I know many of you are desperate for the post on the Vertical Garden. The scaffolding is still in front of it and the minute it’s down I’ll be able to show you it in all its early splendor. Here is a little glimpse of what is flowering at the moment.
Useful Reference: Etekwini Guidelines Document