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Maintenance and Diagnostics

General Types of Maintenance

Compared to green roofs, roof gardens require more frequent maintenance as it includes a wider work scope.

General maintenance helps in upkeeping the intended quality and performance. It also aids in identifying possible future malfunctions and problems. During the design phase, considerations and provisions should be made for maintenance of plants along the edges to ensure safety and accessibility.

Maintenance activities usually include irrigation, application of fertilizer, pruning, mulching. A lab analysis should be done yearly to determine the amount and type of nutrients needed1 .

Fertilisers

Regular application of fertilizer helps to promote healthy plant growth. It can be applied directly to the substrate or onto the leaves. Fertilizers usually consist of major plant nutrients which are nitrogen (N), phosphorous (P) and potassium (K).

Types of application of for fertilizer

  • Solid fertilizer: apply manually onto the growing media evenly
  • Liquid-state fertilizer: it can be applied manually or through an irrigation system1

Pruning

Pruning involves the removal of diseased, non-productive or unwanted parts of the plants. Pruning is regular maintenance to improve the wellbeing of the plants, its size and form1.

Pruning is normally needed once or twice a year, depending on the plant species and its growth rate. This ensures that vegetation does not grow onto building fixtures2 .

Mulching

Mulching is the placing of any approved friable organic product or inorganic material over the surface of the soil as a covering. This helps to hold moisture in the soil, suppress weeds as well as keeping the soil cool. The suitable pH value is between 5.5 – 7.01.

Green Roof

Activities involved in maintenance would depend on the plantings and regional climate where the green roof is located. Basic maintenance involves watering, weeding and plant care5.

The recommended frequency of maintenance is at least once every 2-3 months.

  • Vegetation coverage

At least 65% of the green roof should be covered after pruning. At least 60% of vegetation coverage should be achieved upon 6-8 weeks from the completion of planting stage.

  • Vegetation mat

Vegetation must be firmly rooted to the vegetation mats. Total vegetation coverage should be more than 80% of the green roof, taking into consideration of “seasonal” variations. Visible joints should also not exceed 10% of total joint area.

  • Avoid overcrowding

Overcrowding of vegetation will weaken the vegetation and put a risk of disease infection. This could be due to excessive watering and application of fertilizer, lack of regular pruning or plants have been installed too closely without taking into account the plant growth rate. There could also be excessive growth of weeds.

  • Clear safety zones

There may be some greenery growth on safety zones over time. These unwanted growths should be removed regularly, especially in fire-prevention zones. Deposits or matters that can affect the intended purpose of safety zones should also be removed.

Pitched Green Roof

Erosion Prevention

Prevention of erosion from tropical rainstorm is critical for pitched green roofs. Preventive measures are to be considered. During the design stage and carried out during installation1 .

Preventive measures include:

  • Adequate specifications for the build-up of the green roof system.
  • Temporary and long term effective measures
  • Special measures on specific locations to cater for extreme climatic conditions.

Corrective measures, during maintenance, include:

  • Replace the growing media with one that is stable, porous and of higher density even when dry, to improve the settling of the growing media. Please refer to CS E03:2010 Guidelines on Substrate Layer for Rooftop Greenery.
  • Improve drainage at the critical locations (such as the eave and around the rainwater downpipe) Through the introduction of drainage materials. Please refer to Section 3 of CS E04:2010 Guidelines on Filter, Drainage and Root Penetration Barrier Layers for Rooftop Greenery.

Replace the vegetation with suitable plant species – fast growing, good root system, ground-hugging ground covers, as well as plants that shield the affected growing media from the immediate elements.

  • Safety against falling

Work safety on site should be adequately provided for carrying out maintenance works.

Roof Garden

Maintenance of the roof begins from the first year of installation, with 1 to 2 visits yearly6.

Particular areas require additional attention and care for maintenance. For tall vegetation, stability should be ensured by supplemental support systems. Checks are to be conducted and measures should be implemented to ensure the stability of tall vegetation. Measures to ensure stability includes staking the tree trunk, guying the tree and anchoring the tree root-ball1.

Staking

  • Staking provides temporary stability to woody plants. Design for tall vegetation should allow for adequate root-establishment and root-hold of the substrate volume so as to ensure that there is bio-mechanical stability in the long-term.
  • Metal components used for staking should be rust-proof
  • Plants should be checked regularly during the period of staking.

Guying

  • A tightening mechanism should be used to ensure that  the tightness of the wires or ropes can be adjusted. These can be secured by means of threaded anchors and point ballast.

Anchoring to support-frames

  • Rectangular or triangular supporting frames that are non-corrosive can be used to anchor trees. Frames should be adequately stable and have broad supporting base plates.

Anchoring to dead-man anchors

  • For planter with square area exceeding 16 square metres and with substrate volume and depth exceeding 1.5m, it is recommended to use “dead-man” weighted blocks on the base.

The following procedures are to be carried out in the first 12 months:

  1. Remove unwanted plant material
  2. Rectifying localised plant system problems
  3. Replace failed plants that have exceeded 5% of total plant
  4. Apply nutrients
  5. Prune, mow and remove dead vegetation
  6. Irrigate according to plants’ requirements
  7. Replenish areas of settled substrate

For maintenance of drip-irrigation system, pipes should be connected in the right way. Emitters should be free from infestation of roots or insects etc. Mechanisms should be in working condition and not damaged. Check for mosquito in Drainage system, rainwater conveyance and storage tank.

Inspect all VFZs and roof drains at least once every two weeks.

Maintenance Log

Maintenance activities are to be recorded. Maintenance log and photos should include:

  • Personnel involved in conducting the maintenance
  • Type of plant care carried out
  • Soil testing results and type of fertilizer used
  • Photos of all green roof areas and document plant stress, watering rates, drought periods and replacement of plants

Green Roof Maintenance and Design

  • Plant Selection

Locally grown hardy and drought tolerant plants such as Sedum and mosses are ideal. Maintenance personnel should be well versed with green roof plants and aware of the owner’s aesthetic preference of the green roof, such as intolerance against growth of certain “weeds”7.

  • Irrigation Plan

It is critical to be located near the rooftop and provide accessibility to water, with adequate pressure for supplemental irrigation during establishment and periods of drought (ibid.).

  • Fertilizing Plan

Slow release fertilizer is applied to the plants once a year, usually in spring, to provide them with nutrients over a 3-9 month period. However, these nutrients should not be applied on plants which are preparing to go into dormancy in the fall season (ibid.).

  • Weed Control

Without proper maintenance and weeding, weeds can invade and overtake the green roof. Waterproofing membrane can also be damaged by woody plants. It is less inviting for harmful weeds in a thin layered system with synthetic water retention layers as compared to systems with thick growing medium. Furthermore, less routine and manual weeding is required for thin-layered systems (ibid.).

  • Debris Removal and Drain Inspection

It is important to inspect drainage oaths to prevent blocked drains and pooling of water. This can cause roots to rot and may drown the plants (ibid.).

  • Document Your Visits

When an extensive green roof is well set up, there are usually minimal maintenance requirements. However, there should still be a person or team responsible for conducting maintenance on the system 3 or 4 times a year. If there is no personnel to do this, it is recommended to employ a professional green roof maintenance contractor with expertise in horticulture and trained in working at height. Every visit should be documented and recent weather conditions should be recorded. Photos are a necessity for future reference and any potential warranty claims (ibid.).

  • Maintenance Schedule

The maintenance schedule should be taken into consideration during the design process when there is a foreseeable demand for maintenance input. Maintenance on biodiverse roofs and those designed to be low-maintenance are still needed once or twice a year to clear gutters and drains and remove any unwanted debris or litter8.

  • Other Considerations

What are the key considerations during maintenance?

  1. Undesirable Plants
  2. Irrigation
  3. Fertilisers
  4. Fire Breaks

What are the key technical design requirements of a green roof?

  1. Waterproofing
  2. Up-stand Details
  3. Vapour Control Layers
  4. Outlet Inspection Chambers
  5. Loading Weight

What are the factors to consider when planning a green roof?

  1. Access and Fire Risk
  2. Management of Design
    1. Guarantees
    2. Manufacturers and Supply
    3. Planning Consent/Permission
  3. Roof Structure
    1.  Limited Roof Space
    2. Outlet and Downpipes Requirement
    3. Pitch of the Roof
  4. Design Factors
    1. Biodiversity
    2. Irrigation
    3. Rainwater Harvesting
    4. Solar Thermal and Photovoltaic (PV) Panels

Requirements of building green roof9

  • Suitable type of roof slopes
  • Appropriate adjustments on the design loads
  • Considerations on the effect on drainage and watering facilities
  • Accessibility of green roofs for maintenance staff
  • Provision of protection devices against occurrence of potential falls
  • Presence of root resistant membrane
  • Protection of membrane against mechanical impact
  • Means of assembling the roof outlets
  • Appropriate height at which the membrane is raised above the surface of the green roof
  • Degree of hot or cold air from vents, AC-units or exhausts from chimneys
  • Optimal influence of loads on the different areas of the roof
  • When a green roof can be considered fire-resistant
  • When sloped roofs require special measures against slipping of the green roof
  • Means of constructing paved areas

Maintenance Contract

A Maintenance Contract should be made between the Owner and Landscape Contractor for the upkeep of the rooftop greenery. The contract should include the objectives, scope of work, duration and frequency and a Maintenance Report should be submitted after every round of maintenance.