Garden, Gardens

Growing a Green Roof

We recently asked local horticulturist Zayaan Khan for her tips for those looking to build their very own green roof at home. As it turns out, it's a lot more manageable than you might think... What factors do you need to consider if you want to install your own green roof?

  • First and foremost you must ensure your roof is sound to support the weight of a saturated green roof system – determine what the weight of the entire system could be on the wettest day. A consultation with a structural engineer is essential to do the assessment. Roofs are generally not built with holding capacity in mind, so it is better to incorporate it into the initial design and planning if you have that luxury. The engineer will then be able to guide you on what changes need to be made to existing roofs to fit the specified outcomes and green roof desires. For example, do you want to install trees, if possible? Do you want to create a simple extensive green roof or are you planning on using the roof as a space to enjoy, to entertain?
  • Once this is settled and a roof is possible, the fun begins. The most important aspect of the system is the waterproofing and protection of the underlying roof structure. Installation must occur as soon as the waterproofing has cured to prevent weakness in the layer. It is important to remember that roots can seek out any crack and crevice, so the protective layer must be done soundly, and that a root protection layer is essential.
  • The biggest consideration is cost, which is not easy to judge at the outset. A good idea is to plan out what it is you want in the green roof and break down the budget accordingly, before jumping in. The roof system needs to be installed in one go to ensure its success.
  • It is also important to remember that green roofing is new in South Africa and there are no hard-and-fast rules, so you must use the opportunity as research, an experimentation of what works and what does not according to where you are and what kind of roof you have. For example, is your roof made of concrete slabbing or metal sheeting or tiles? Perhaps experiment on the garage roof first or maybe on the afdakkie or awning – starting small gives you an idea of what it takes to tackle a bigger project, as well as the time, cost and input.
Which plant types work best for green roofs? The plant availability in our country is almost endless, with many species naturally growing in low mediums and 'harsh conditions'. A big factor we have is heat and wind – these need to be taken into consideration when choosing the plant species. The easiest, low-maintenance plants would be plants such as sprawling succulents and low-growing drought- and heat-tolerant plants, also ideally plants that do not have an aggressive root system. Good options are vygies, Gazanias, low-growing aloes, grasses and bulbs. What maintenance is involved in having a green roof? Maintenance depends on the type of system you have and the plants themselves. The foundations, when done correctly, do not need maintenance. Intensive systems generally have bigger plants that may need pruning and tending. If you install irrigation, it may need maintenance from time to time. Extensive systems generally run maintenance-free. But it really depends on what you install. Bigger systems that are more complicated are best left to professionals. Tips for starting your own green roof from scratch?
  • Start small and keep it simple!
  • The toughest aspect of doing your own green roof system is the initial research – you must understand how it works before you commit.
  • Once that is done, the most important are the foundation layers: ensure each layer is done to its utmost, do not cut any corners.
  • Ensure the plant choice is suitable. Remember the water-holding capacity of the soil is less so it is better to use water-wise plants.
  • Also, it is always better to plan, measuring up the area so your quantities are right and doing a planting plan will ensure any unwanted surprises in the installation.
For more information you can visit Zayaan's blog or contact her on zayk.first@gmail.com. You can also read more about the subject of green roofs here.