Roof/Sky Garden

Good Practices

Roof gardens are designed for usage. Hence, regular maintenance is required. For instance, mowing, fertilising, watering and weeding. Plants selected for green roofs are usually of low maintenance and are self-generated. Inspection should be carried out minimum once or twice a year¹.

Checks & Maintenance 

• Remove errant green roof vegetation and any debris such as pebbles, sticks, leaves, trash, etc. from drainage system and drain paths to ensure the roof drains to function correctly.
• Trash, pebbles, sticks, fallen leaves etc. are removed from the green roof regularly. This is because they can help to smooth the green roof plants.
• It is vital to remove the tree seedlings in an appropriate timing in order to avoid their strong root systems from compromising the waterproofing system.
• All valve locations and joints should be checked to detect for the signs of leaks or breaks in the piping.
• Spray heads and drip emitters can be inspected visually to confirm that they have not become clogged.
• On the condition that using an automatic system, the moisture levels on the roof should be checked and the run time on the controller should be adjusted³ .

Checks on Drainage and Other Under Layers

• Checking on under layers

It is a good practice to visually inspect at least once if not twice a year by doing a cut-and-cover exercise for the under layers of the green roof and roof garden. Besides, for visual inspection, the layers or components that form the build-up of the green roof and roof garden systems are to be cut open and ripped one at a time till the bottom-most layer or component is exposed. After that, they are covered up or reinstated carefully one at a time.

• Checking on drainage fixtures
• Drainage fixtures should also be checked visually on a regular basis

Pest Infestation

Inspection for pest infestation and disease infection for all plants should be carried up periodically. Any pests, pest infested plant parts, diseased plant parts or diseased plants are to be removed immediately upon notice.

In order to avoid their introduction to the run-offs and eventually, the groundwater, the use of herbicides, pesticides, fungicides and similar products are discouraged. Use such products only when necessary and not on a regular basis.

For more details on tropical plant-diseases, plant-disease-identification and plant-disease-rectification please refer to the following publication by CUGE (Centre for Urban Greenery and Ecology) – Tropical Gardeners’ Guide to Healthy Plants and Pictorial Guide in CD (ISBN: 978-981-08-6286-2).

Checks to ensure stability of tall vegetation at the rooftop

It is necessary to check and ensure the stability of tall vegetation at the rooftop for roof gardens. Groundcovers and low-lying plants are often planted on roof garden while tall vegetation such as big shrubs, hedges and small trees are frequently planted on roof gardens.

In order to provide additional support to leaders, individual limbs, and/or the whole plant, supplemental support systems which include staking and guying are used. Prior to installation, the objectives for support systems shall be clearly defined¹ .

Installation of staking and guying can take reference from the methods and standards specified in the latest ANSI A300 Part 3 and should be read in conjunction with the rest of the ANSI A300 when carrying out such installations³.

There is a need to implement measures and to conduct subsequent checks for tall vegetation such as tall shrubs, trees and palms, on rooftop to ensure the stability of this tall vegetation. Furthermore, stability measures that can be applied include staking, guying the tree trunk and also anchoring the tree root-ball¹.

Design

In green objectives, in order to fulfil different intentions and purposes, the common rooftop greenery is designed to be an:

• Aesthetic-ornamental (i.e. “manicures”) garden. The consumption of fertiliser for the roof gardens is usually high as the landscape is designed to provide spatial and visual appeals to the users.
• Ecologically optimized (ie “naturally developing”) greenery. The consumption of fertiliser is normally less than the above-mentioned. This is because the landscape for green roofs is designed to allow the vegetation to develop naturally over a period of time without human intervention.

Plant Type

Drought tolerant plants are recommended for green roofs because the wind speed increases with altitude, the rate of moisture loss increases as well, especially along the edges and corners of the green roofs and roof gardens. Besides, classifying zones based on different watering needs can ease the way to irrigate the green roof. In order to minimize evaporation losses, water the plants between 4-7am or 6-9pm. Furthermore, by installing private water meter at irrigation system can help to monitor the water consumption and to detect any water leakage. The use of Water Efficiency Labelling Scheme (WELs) labelled fittings with minimum Very-Good-Rating is encouraged. The drip irrigation piping should preferably have design provision to counter plant-room penetration as the plant roots may clog up drip holes⁴

Water Storage Methods

Substrates are designed to retain water by concealing water retention boards or mates within substrate layer to enhance water retention capacity. For instance, rock wool and foam boards. The drainage layer which made from open-pore water-retaining aggregate materials in graded granular sizes or pre-formed drainage boards are used to retain water. Besides, for example, moisture retention mat is used as water retention protective layer on green roof. Substrate used should prevent drying out by keeping it mist and thus erosion from strong winds, especially during the set-up phase of the vegetation (ibid.).

Water Storage Capacity

Aggregates in aggregate layers should have the properties of high drainage and water storage:

• Closed-pore as opposed to open pore. For example, crushed expanded clay is more suitable than uncrushed expanded clay)
• Water-repelling as opposed to water-absorbent.

This is to make sure that the maximum dry space is higher than the maximum water table within the drainage layer to avoid water-logging of the substrate layer.

In order to prevent erosion of substrate:

• Higher density of substrate mixtures are used even when dry.
• Additional layer of hard stone chippings such as pebbles can be installed on top of the substrate.
• The species of plant used are ground covering, fast growing and long lasting.
• Keep it Moist Soil fixer/ conditioner Erosion Protection netting such as jute net which made of decomposable materials is a temporary measure that can be used (Ibid.).

Filter Layer

1. Filter layer should contain substrate layer and retain it to prevent loss of aggregate and substrate volume, especially where the substrate layer is thin on green roofs.
2. Filter layer uses plant debris to prevent clogging of the drainage layer but still allow air and water to pass through.
3. Appropriate chemical and physical properties in filter layer is to ensure filter layer can be function appropriately under unique site conditions, while not hindering the growth of vegetation and establishment of root (Ibid.).

Water Permeability

Materials are designed to be highly permeable to ensure water permeability. Besides, during heavy downpour, surface runoff should be expected for extremely thin and shallow rooftop greenery system. An insignificant amount or no surface runoff should have designed for green roofs. The performance of ductile drainage layers depends on the depth and coefficient of permeability. Lastly, due to chemical factors, stable, durable and inert mineral aggregates are advisable. This is because aggregates may reduce in granular size (Ibid.).

Stability

• Certain level of integral strength should be found in materials for load bearing purposes which comprise of material and overlying material or structure’s weight, water’s weight especially when saturated and weight of loads that produced during maintenance and serving activities.
• Rot and crack resistant properties must be found in drainage boards and mats even under the influence of materials and microorganisms in the vegetation layer.
• In order to maintain the efficiency of the system, the drainage system has to be rodent and resistance to vermin.
• It is discouraged to use sharp and extremely angular grained aggregates which can affect the stability of material during installation (Ibid.).

Staking

• Staking helps woody plants to provide temporary stability and it is vital to provide adequate overall depth or thickness in the substrate layer and also the support layers that forms the roof garden system, for the roots of tall vegetation to establish and take hold. Roots are established to provide the long term anchorage for tall vegetation. Design provision permitting for enough root-establishment and root-hold of the substrate volume with tall vegetation, over a period of time, it is important for the tall vegetation to have a long-term bio-mechanical stability.
• It must be rust-proof if the metal components are used as part of the staking systems.
• Throughout the period of staking, the plants are required to be checked at regular intervals which is once in 3-4 months for signs of constriction and rubbing. Adjustments can be made to the design of the staking if necessary in order to tighten or loosen the hold on the plant.

Guying

• In order to ensure the tautness of the wires or ropes can be adjusted from time to time, guying should be fitted with a tightening mechanism.
• The various ways to secure these are as follows:
  • Set threaded anchors without penetrating the waterproofing membrane into the building structure and should also be designed with a screw-thread connector.
  • Design suitable construction elements in order to keep the tree in place. To quote an instance, roof edging, walls, large paving slabs.
  • Point ballast. For example, slabs or blocks laid within the build-up of the roof garden system that act as a ballast or plinth or anchor point for the wire or robes. It is vital to make sure that any load-bearing properties of the roof garden system or the thermal insulation are not affected by the loads of these point ballasts negatively. Moreover, an angle of less than 600 to the horizontal is formed for the wires and ropes to these point ballast.

Anchoring to Support Frames

• When anchoring the trees, it is more suitable to use rectangular or triangular supporting frames.
• Support frames usually made up of steel pipes or tubing with surfaces treated against corrosion.
• Adequately stable and board supporting base plates are required for each frame.

Anchoring to dead-man anchors

• The use of “dead-man” weighted blocks on the base of the planter is recommended for trees on the rooftop provided the planter is broad with a square area in excess of 16 square metres, with adequate substrate volume and depth exceeding 1.5m.

Fertilisers

The following listed factors are depended largely on the amount and type of fertiliser used:

• The inherent nutrients in the growing media.
• The green objectives.

Mulching

For rooftop greening, the mulch material should be properly stored with sufficient space allocation and in bags) and sheltered from the elements. Besides, priority should be given to site conditions of the rooftop greenery when deciding on the type of mulch used, including wind effects that may sweep the mulch material away. Depending on the type of vegetation, the thickness of the mulch layer is normally about 25-100mm while the mulch layer can be as thick as 100mm for tall trees.

pH Values

The pH values for substrate layer have to be at a maximum deviation of 1.5 units and should be similar with the drainage layer (Ibid.).

Carbon Content

Drainage layers with high carbon content, for instance, recycled concrete and calciferous aggregates must not be used because of the risk of drainage impediment by sintering. In order to prevent carbonates from being dissolved by discharging water, the roof surfaces should be coated or sealed with a plastic sheet if sintering is inevitable (Ibid.).

Safety

A useful reference is the CS E02:2010 – Guidelines on Design for Safety on Rooftop Greenery, Section 2.2 – Safety Considerations During Installation & Maintenance Phase. This is because maintenance works of the rooftop greenery is usually carried out at a height. Hence, during maintenance, measures must be taken in place to ensure safety of the workers and also to stay away from objects and/or plant debris falling from height.

Fall prevention

• Protection measures against falling are required and must be implemented for all rooftop greenery works on superstructure components that are more than 3m above ground.
• During the execution, construction, maintenance and servicing of green roofs and roof gardens, fall prevention is relevant throughout the life of the building.
• Use only approved products and systems and consider and adopt the suitable measures and entry features such as cordons, lanyard rails, fixed climbing rails with fall protection
• Fall protection systems in the form of railings or roof scaffold during the construction stage are essential and can only remove after the completion of the rooftop greenery.
• Utilise the restraint- ropes of suitable lengths with the pre-installed anchors or other fall prevention systems for maintenance and servicing work.
• Install the retrofitting anchors on already-completed and waterproofed roofs without compromising the waterproofing system that is already in place.

Fire Safety

• Remove any vegetation encroaching onto the safety margin or vegetation-free zone to ensure fire safety on a roof garden or green roof
• Safety margin is a general rule to provide vegetation-free zone or strip or margin comprising stones a separate vegetation areas from the structural components (such as walls and columns) or protruding facilities (such as windows, doorways, ventilators, air-wells, skylights, air-coolers, water tanks, etc) of the building. Depends on the fire-sensitivity of the item to which the vegetation abuts, the width of the safety margin ranges from 250 to 500mm.

The table below is the recommendation frequency of pruning (including mowing of turf):

Back to Previous Page