GUIDELINES TO SET UP A ROOF GARDEN
GUIDELINES TO SET UP A ROOF GARDEN
During COVID 19 pandemic, every action of the human beings is very crucial. The various containment measures such as lockdowns, quarantines, and curfews have been taken by different countries around the world. In Tamilnadu, Koyambedu market is the epicenter of the coronavirus disease. So, this pandemic changes the way to serve vegetables and fruits each day. The safest way to purchase the vegetable is to cultivate it by ourselves in the roof garden.
The Roof garden implies the garden on the roof of the building. Roof gardening is not new to the world. Since the period of Ziggurats of Mesopotamia, the humans have started to grown plants at the top of the structure. Among the seven wonders, the hanging Gardens of Babylon shown in featured image is one of the tallest structures to hold vegetation.
According to Civil Engineer, the roof garden provides the following benefits
Green top controls CO2 emission and produces oxygen
It controls the temperature so automatically reduces the heat of the building
It enhances the architecture of the building
It makes large catchment areas as well as reduce the stormwater runoff
It captures and harvests rainwater
The other benefits are,
It provides recreational opportunities
It creates corridors for wildlife
It enhances the resale or rental value
Design key points of roof garden system
Many countries have their original guidelines to design a roof garden system. It mainly depends on the type of vegetation, slope and drainage, climate condition, accessibility, and building configuration, etc. Based on these criteria, the extensive or intensive roof garden system has the following components and it is shown in Figure 2.
• Structural deck
• Waterproof membrane
• Drainage layer
• Filter sheet
• Growing medium
Structural deck
Firstly, the structural deck already exists in the building ensured with the provision of expansion joints, ductwork, and piping. Secondly, the surface should be noted for defects and unsound patches. Thirdly, the surface is cleaned for smooth and dirt free surfaces.
Waterproof membrane
The waterproof membrane is provided at the bottom of the roof garden system to protect the slab from the drainage and root penetration. It must be durable enough to resist the mechanical energy like roof gardening tools during the installation and maintenance process. The waterproofing of the top surface can be achieved by the application of waterproofing liquid or by providing the waterproofing sheets.
Drainage layer
The facility provided for runoff water laterally from the roof to prevent the structural collapse. So, the drainage layer will protect the waterproof membrane. In case the drainage is not adequate then the waterproof membrane will be in contact with water or wet soil continuously. These types of drainage layers are applicable for flat surfaces. Sometimes it also used for the surface having a slope less than 5 degree. The drainage layer may be one of the followings
Granular materials – Stone chips, coarse granules of gravel, LECA, pumice
Porous mats – Mats made from recycled materials such as clothing, car seats
Lightweight plastic or polystyrene drainage modules – Density Poly Ethylene (DPE), High DPE or High Impact Poly Styrene is used
The disadvantage of a porous mat is that it may absorb too much moisture from the growing substrate or become too light when dry. Sometimes the mat itself decomposed or shrink over time because of recycled material. To clear the blockages or stagnant water, the drainage outlets should be connected by the vertical piping to the surface of the growing medium.
Filter Sheet
The filter sheet is used to prevent the entry of fine material or other contaminants into the drainage thereby protecting the drainage from clogging. Nowadays geotextile is used as one of the filter media. Geotextiles are non-woven, needle punched fabrics designed for separation applications.
Growing Medium:
The Growing medium is provided with the lightweight aggregate-based medium for long and short term success of a green roof. The essential requirements of growing media are as follows:
Bearing capacity of soil
Nutrition supply
Permeability
Lightweight
Water retention capacity
Fireresistant property
After installing all the components of the roof garden system, the additional key parameters are the plant species selection, irrigation system, maintenance, and cost.
Selection of Plant Species
The critical plant selection criteria depend on the growth potential in lightweight shallow soils, tolerance against wind and drought, non-invasive roots, nutrient demand, function, and maintenance investment. Horticulture suggests the different depths for different vegetation. For example, the root growth rate for moss and sedum is 4 – 10 cm, for herbaceous plants are 5 – 11 cm and for grass 15 – 25 cm.
Irrigation system
Extra watering should be carried out regularly at the roof garden. There are three types of irrigation system involved in this namely,
Manual irrigation
Automatic irrigation
Semi-automatic irrigation
Maintenance
On the other hand, these roof gardens are established for human usage thereby maintenance is one of the important requirements. So the periodic maintenance is required for landscape portion.
Cost
The capital cost of the roof garden includes many factors such as the location of a roof garden, depth of growing medium, type of plants, method of irrigation, waterproofing area, and other accessories.
Conclusion
The Roof garden is a big investment in the short term but it provides the benefits for long term. In the olden days, the roof garden systems were considered only for luxury purposes. Nowadays starting from the small scale to large scale projects are started to adopt roof garden systems. Finally, it increases energy efficiency as well as roof life.
Web Sources
http://agritech.tnau.ac.in/horticulture/horti_Landscaping_roofgarden.html
https://www.drfixitinstitute.com/download/rebuild_2013/Rebuild-vol-7-no4-oct-dec2013/Rebuild-Vol-7-No%204-artical-1.pdf
References:
1. Derek Townshend (2007), “Study on Green Roof Application in Hing Kong”, Report submitted to Architectural Services Department
2. Siew, Z. B., Chin, C. M. M*, Sakundarini, N. (2019), “DESIGNING A GUIDELINE FOR GREEN ROOF SYSTEM IN MALAYSIA”, Journal Clean WAS (JCleanWAS)3(2) (2019) 05-10