How to Build a Roof Garden

The concept of a roof garden is not a new one. In fact, it is centuries old!. If you live in an urban area, your dreams of having a garden may be difficult to achieve. Not so if you consider a roof garden!

More and more communities are encouraging their residents to plant roof gardens. The environmental and psychological benefits are numerous. Not only is gardening a calming and relaxing activity, which can reduce stress related illnesses, it also has great benefits for the environment. Building a rood garden on your home or apartment building decrease storm water runoff, reduce fire risks, help decrease heating and cooling costs and can protect your roof from the effects of ultra-violet light and frost. 

There are three types of roof gardens and the three types related to the amount of maintenance they require, the depth of soil and the type of plants they will support. They are:

 Extensive living roofs

These are easy to maintain and use little soil. Extensive living roofs are lightweight and lend themselves well for use on sheds, garages and small extensions. As they tend to be harsh environment, suitable plants are ones that are found on cliffs or other harsh environments. While this type of roofs gardens are the easiest to maintain, they also have the least visual appeal. 

 Semi-extensive living roofs

These garden roofs are more decorative as they have deeper soils which can support a greater variety of plants. However, the increased soil depth makes these types of roof garden more heavy, so a sound structure is require to support them. They combine the relatively low maintenance of extensive living roofs with a more appealing appearance.

 Intensive living roofs

These are full-fledged gardens and require large and strong support structures. 

One of the main considerations when planning a roof garden is the roof itself. While flat roofs lend themselves the best to roof gardens, it is also possible to green pitched, barreled and domed roofs. An easy access to the roof is also important as I am sure you would not be able to enjoy your roof garden as much if you have to climb a ladder every time you want to look at it. The roof must able be able to support heavy loads. Wet soil can weight about eighty pounds per square foot. 

Make sure you install a waterproof membrane to avoid ending up with a wet ceiling. The two most commonly used materials are thermoplastic sheeting or rubberized asphalt. As I am certain that you will not want to dig up your garden to replace the membrane every few years, make sure you select a product that is extremely durable. The next layer should be a filter sheet that will allow the moisture to drain off the roof while ensure that the fine material do not escape. Next comes the moisture blanket which will ensure that an extensive live roof garden has enough moisture to support life. Commercial ones can be purchased however it is also possible to use cardboard or old blankets to the same effect. 

The following layer will be a drainage layer. Similar to the moisture blanket, it will help retain moisture while allowing excess water to drain away. They are usually made of plastic or geotextile materials. The top layer will be the soils and substrates. These should be lightweight and freedraining yet retain moisture. One such option is an aggregates mixed with light sub-soild such as crushed porous brick or limestone chippings. Finally come the seeds and plants. The possibilities are limited only by your imagination and the environment. Happy gardening!