SEMI - EXTENSIVE ROOF GARDEN
 What is a Modular Extensive Roof Garden: (MERG)
The key to this product is the instant garden effect using these portable modules. Comprises of a shallow profile of between 80 – 100mm. The modules are made of UV stabilized shadecloth and filled with a Hydrocell mix into which are planted prostrate/low growing plants including mosses, sedums and stress tolerant grasses. These systems are portable, lightweight and require minimal maintenance. Up to 90kg per sqm in weight. These roofs are generally not readily accessible and are used primarily for environmental and economic benefits as opposed to recreational space. Under Australian conditions the installation of basic irrigation would be advisable as insurance.
Photo: Note the layering: LDPE, upturned drainange cell, modular profile and plants.
The Fytogreen Modular Extensive Roof Garden System (MERG)
The “magic” of the modular system is that it is portable. Plants are planted and pre grown in the modules off site using the lightweight water retentive substrate called Hydrocell RG30. This remarkable material makes possible the construction of a long lasting lightweight, water storing roof garden.
Hydrocell RG30 is a foamed aminoplast resin made as a special RG30 flake, which is mixed with special components and bagged to form the basis for modular extensive roof gardens.
The RG30 Hydrocell component replaces part of the traditional gravel layer on extensive roof gardens and becomes part of the growing media on modular extensive roof gardens. Hydrocell is lighter in weight, increases usable media volume, has significantly higher water and nutrient holding capacity. It also acts as a capillary mat returning water to the top of the profile. A fines filter protecting the geofabric layer and improving the quality of the stormwater.
Fytogreen’s Modular Extensive Roof Garden Profile (MERG)
Role of the various layers in the profile.
Waterproof membrane:
The building roof should have a sealed waterproof layer installed before work on the roof garden begins. This is commonly called tanking and is certified independently by specialized contractors.
LDPE Sheet: This is an extra waterproof sheet, which acts as a protection layer both from water and plant roots for the waterproof membrane layer.
Retainer Bars: These are to stop slippage of an extensive roof garden when the roof pitch is between 10o and 30o. They are made of different materials to suit the roof type on which they are being installed.
Drainage Cell: Critical in allowing excess water to escape the roof garden profile quickly to the drainage outlets. The cuspated drainage cell is installed “cups up” to provide a water reservoir of up to 4 litres per m2 that the plants can draw on.
Geofabric Layer: This minimizes fine soil particles from reaching the drainage system.
Media Grids: For pitched roofs over 10o, media grids are installed between the retainer bars to prevent module slippage.
Hydrocell RG30 Flakes: A percentage of 50% is used in the module to increase usable media volume, lower rooftop weight while at the same time increasing stored water reserves for plant use. The 50% component will hold up to 24 litres of water per m2 and is able to be gifted back to the soil mix. Hydrocell RG30 also acts as a filter for soil fines. Hydrocell has a high compressive strength and is very durable under a range of climatic conditions.
Hydrocell 40 Extensive Soil Mix: The module contains 50% of this mix. The components of the mix are 40% Hydrocell flakes providing a lightweight media that holds plant available water throughout the profile. It has excellent capillary properties and has a component or air, which helps the profile to drain quickly.
Scoria or recycled concrete provides an open mix allowing good drainage and structural stability with composted organic matter providing some nutritional value.
Roof Garden Edging: Required on retrofit roof gardens where a structural parapet is not available or possible. Is fixed in place in conjunction with the water proofing process.
 Advantages of Fytogreen’s Modular Extensive Roof Garden System (MERG)
-Portable pre grown modules for an instant garden
-Under Australian conditions Hydrocell provides a much needed water reservoir
-Huge water holding capacity while saving weight. Hydrocell RG30 flake component at 50% of the mix has a water retention capacity of up to 24 litres per m2. The dry weight of this Hydrocell component is 1.5kg/m2 compared with the same amount of dry Coarse river sand at 56kg per m2 and very little water holding.
-Lightweight, which offers more flexability for lower static loads on building roofs
-High water holding capacity and increase in usable media volume enabling low soil profiles
-Grey water and storm water compatible with no toxicity or harmful effects to the environment. Hydrocell is biodegradable and non-flammable
-High compressive strength means hydrocell can hold a great weight
-Durable even under extreme climatic conditions giving longer life
-Can be built on almost any roof capable of taking the weight with a pitch up to 30o
-Prolongs the life of the water proofing membrane
-The excellent capillary properties of Hydrocell ensure improved availability of water to plant roots and a moreuniform water distribution on pitched
-Easy and very quick to install
Photo: End view of two MERG modules butting together.
WHY USE HYDROCELL RG30 FLAKES
- Increased longevity up to at least 25 years
- Increased Water holding capacity
- Improved compressive strength for foot traffic conditions
Minimum Roof Load
Fytogreen’s Modular Extensive roof garden system is lightweight with over 50% of weight being retained water for plant growth. Very light in comparison with other systems.
The saturated weight allowance for a modular extensive roof garden with a 100mm profile is 90kg/m2 including vegetation.
 Application Procedure
Laying the system is a specialized job. Great care must be taken to avoid damaging the underlying waterproofing. The system is laid in the following order:
- Waterproofing, including the provision for Retainer Bars for pitched roofs over 10o and Garden Edging on a retrofit. (completed by an independent contractor)
- LDPE sheet
- Fytonop 20 Drainage cell – cups up
- Geofabric layer – Bidim A14
- Modular Extensive Roof Garden-water retentive growing medium
- Subsurface irrigation system threaded along the middle of each module. Required for drought insurance
- Enjoy your garden
Plant selection:
With a modular extensive roof garden plant selection is both limited and critical due to the harsh Australian conditions as a result of shallow profile depth and moisture availability. Low maintenance planting includes ground covers, sedums to native grasses. Still you must take into account water availability, sunshine hours, wind force and direction, location of the building and latitude.
Maintenance and Irrigation:
Extensive roof gardens in nortern hemisphere countries do not often require an ongoing irrigation system. However with Australia’s, harsh climate it is worth installing a basic subsurface irrigation system for safe plant establishment and as an insurance against prolonged drought periods. The project can be designed sustainably by Fytogreen with the inclusion of rainwater tanks utilizing the drainage water from the roof. Fytogreen recommends irrigation installation to protect your investment.
Low maintenance plants should be selected but maintenance will include the removal of unwanted plants such as weeds, checking drainage outlets and an annual application of slow release fertilizer each spring.
Photo: The modules butt closely together and become indistinguishable as plants grow.
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