Extensive Roof Garden

EXTENSIVE ROOF GARDEN

WHAT IS AN EXTENSIVE ROOF GARDEN?

Consists of a shallow profile of between 50 – 100mm, planted with prostrate/low growing plants including mosses, sedums and drought tolerant grasses. These systems are lightweight (Up to 100kg per m2 in weight) and require minimal maintenance. 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 is recommended for insurance against prolonged dry periods.

THE FYTOGREEN EXTENSIVE ROOF GARDEN SYSTEM

The “magic” of the system is the lightweight water retentive substrate called Hydrocell RG30. This remarkable material makes possible the construction of a long lasting lightweight, water storing, efficient roof garden.

Hydrocell RG30 is a foamed aminoplast resin made as a special RG30 flake for extensive roof gardens and planter boxes, which can be applied using 1m3 bulka bags.

The RG30 Hydrocell flake layer contributes to part of the growing media on extensive roof gardens in place of the gravel layer. Hydrocell is lighter in weight, increases usable media volume and has significantly higher water and nutrient holding capacity. It also acts as a capillary mat returning water to the above soil, a fines filter protecting the geofabric layer, and improving the quality of the storm water.

FYTOGREEN’S EXTENSIVE ROOF GARDEN PROFILE

ROLE OF THE VARIOUS LAYERS IN THE PROFILE.

Waterproof membrane:
The building roof must have a sealed waterproof layer installed before work on the roof garden begins. This is commonly called “tanking” and is installed and certified independently by specialized contractors.

LDPE Sheet: This is an extra waterproof sheet, which acts 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 10° and 30°. 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 10°, media grids are installed between the retainer bars to prevent media slippage.

Hydrocell RG30 Flakes: A depth of 40mm is used to increase the usable media volume (enabling thinner profiles whilst maintaining a diverse plant species list), lower rooftop weight while at the same time increasing stored water reserves for plant use. The 40mm layer will hold up to 18 litres per m2 and is able to be gifted back to the soil above via its’ capillary properties. Hydrocell RG30 also acts as a filter for soil fines. Hydrocell RG30 has a high compressive strength and is very durable under a range of climatic conditions.

Hydrocell 40 Extensive Roof Garden Soil: A depth of 40mm is used with the components being:
40% by volume Hydrocell flakes providing a lightweight media that holds plant available water throughout the profile. It has excellent capillary properties and has a component of air, which helps the profile to drain quickly.
Scoria (or similar) provides an open mix allowing good drainage and stability with composted organic matter providing some nutritional value.

Garden Edging: Required on retrofit roof gardens where a 125mm garden edge has not been provided for in the construction. Is fixed in place in conjunction with the water proofing process.

ADVANTAGES OF FYTOGREEN’S EXTENSIVE ROOF GARDEN SYSTEM

Under Australian conditions Hydrocell provides a much needed water reservoir
Huge water holding capacity while saving weight. Hydrocell RG30 Flake layer, when applied as a 40mm deep layer has a water retention capacity of up to 18 litres per m2. The dry weight of this Hydrocell RG30 layer is 1.2kg/m2 compared with the same depth of dry Coarse river sand at 56kg per m2 and very little water holding.
Lightweight, which offers more flexibility for lower static loads on building roofs or option to increase the depth and expand the species list.
High water holding capacity and increase in usable media volume enabling lower soil profiles.
Grey water and storm water compatible with no toxicity or harmful effects to the environment. Hydrocell is biodegradable and non-flammable.
Durable even under extreme climatic condition giving a longer life.
Can be built on almost any roof capable of taking the weight with a pitch up to 30°.
Prolongs the life of the water proofing membrane.
The excellent capillary properties of Hydrocell ensure improved availability of water to plant roots and a more uniform water distribution on pitched roofs.
Easy and quick to install.
Fytomat is a pre-grown mat of sedums and/or native grasses, available on request to provide that instant green roof finish.

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 Extensive roof garden system is lightweight with over 50% of weight being retained water for plant growth.
The saturated weight allowance for a 100mm profile is 61kg/m2 plus an allowance for Fytomat at 20kg/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:

Water proofing, including the provision for Retainer Bars for pitched roofs over 10° and Garden Edging on a retrofit. (Completed by an independent contractor)
LDPE sheet
Fytonop 20 Drainage cell – cups up
Geofabric layer – Bidim A14
Media Grids if the pitch is above 10°.
Hydrocell RG30 Flakes – water retentive growing medium
Subsurface irrigation system for garden establishment and drought insurance
Hydrocell 40 Extensive Roof Garden Soil
Fytomat or mulch mat.

PLANT SELECTION:
With an extensive roof garden plant selection is both limited and critical due to the harsh Australian conditions as a result of the shallow profile depth and moisture availability. Low maintenance planting includes ground covers, sedums and 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 northern 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 will be required each spring.

Important Data

Extensive Saturated Weight Guidelines – Extensive 40:40

Case Studies

Cley Marches, UK

Burmondsey. UK

Horbury, UK

Norway Back to Nature Roof Garden

Norwegian humpy with a roof garden being installed.
Water proofing protection layer and drainage cell installed prior to foaming.
Foaming completed

Norway Extensive Roof Garden Installation Foaming an extensive roof garden in Norway. Restraint bars made of timber for the 28° pitch. Roof completely foamed. Roof completely foamed, with the ridging providing a soil keying affect. Hydrocell 40 Extensive soil mix being spread on the roof. Sedum vegetation mats being laid