Roof Garden System

INTRODUCTION TO ROOF GARDEN SYSTEM

According to D. Nigel and K. Noel (2004), a green roof is a green space created by adding layers of growing medium and plants on top of a traditional roofing system. The construction and success of system depend on the specific needs and conditions of site. A roof garden is any planted open space, intended to provide human enjoyment or environmental enhancement, which is separated from the earth by a building or other structure (O. Theodore, 1999).

Commonly green roof is composed of simply at least two layers: the vegetation itself and the media or substrate within which they are growing. In addition most commercial green roof systems will also consisted of five or six components including, above the roof deck: a waterproof membrane, a protective layer, the growing medium, vegetation materials, and irrigation system. (D. Nigel and K. Noel, 2004 ).

Many of the problems associated with green roofs are a result from the faulty installation of one or more of the layers during the construction works and careless maintenance practices (D. Nigel and K. Noel , 2004 ).

Illustration of Roof Garden.
Section Of Typical Roof Garden

( Source : www.greentechitm.com )

Same with other roof on which it is to built, a roof garden is constructed in layers and the garden is in turn intimately connected to the roof. The roof top garden should include at least 4 essential component layers such as plantings, paving, furnishings and water features or sculpture. Once the design has been determined, installation is the key concern. The failure when installing the roof top garden component can cause significant damage to building and make it costly to repair it back. The importance thing that we should consider is choosing the highest quality of materials.

STRUCTURAL CONSIDERATION

Basically, roof garden can be separate into two type of roof garden that is intensive and extensive green roof. The differences between two types of roof garden are their visual appearance and in the amount of maintenance they may require, fundamentally, the division exists because of their relative overall weights.

Extensive gardens require minimal maintenance and behave as another from of roofing material. They are not intended for heavy foot traffic nor do they need to meet any additional safety standards. The intensive gardens created with the intent of active human use. These gardens require landscaping and regular upkeep. The intensive gardens may also need to comply with safety regulations regarding decks and public areas on raised structures. These regulations may require some kind of fencing or barrier to be installed with the intent of preventing people from slipping over the edge of the roofline. (source : http://www.interlog.com/~rooftop/greening.html).

The consideration that we need before choosing the type of roof garden is possible, therefore, relates directly to be load-bearing capacity of the roof structure of the building.

According to D. Nigel and K. Noel (2004), when calculating loading, “it must be remembered that the weight of green roof materials will vary greatly depending on how compacted and how moist they are” (page 59). Saturated weights of materials will indicate their maximum loading. The existing roofs measures can be taken to give additional support if necessary. Strengthen the roof with strategically placed additional structural components such as columns, beams and braces. Place the heaviest components of the roof on or near column heads and over beams. We should consider system that attach the green roof to wall or on small structures, such as garage or outbuilding, or consider constructing a framework around the building that enables the green roof to sit clear of the existing roof.

The typical loadings of extensive green roof system range from 80 to 150 kg per square meter. This is in contrast to typical intensive green roof loadings of 300 to 1000 kg per square meter or more (D. Nigel and K. Noel, 2004).

Table 1: Typical Loadings

INTENSIVE --------------EXTENSIVE
80 – 150 / sqmc -----------300 – 1000 / sqm

( Source : D. Nigel and K. Noel, (2004), “Planting Green Roof and Living Walls”, Timber Press Inc, Portland, Oregon, USA.)

a) ROOF SLOPE

Slippage is the major problem when we are talking about green roof sloped. Basically no green roofs avoid having a fabric membrane or membrane interface for example, at root barriers and sheet drains. Without additional slope stabilization measures, it is unwise to design green roofs for slopes steeper than 2:12, which equals around 9.5o or 17% slope (D. Nigel and K. Noel, 2004).




A Wooden Grid Provides Further Stabilization. We can solve this problem by the use of horizontal strapping, laths, battens, or grids. Finally by using these methods, green roof can readily be constructed on pitches up to 7:12 which equal 30o or 58% but to build on steeper than that we should use special media mixes and specialize devices.

b) STRUCTURAL / LOAD BEARING

Structural engineers divide loads into two categories: “dead loads” and “live loads”.
The Dead Load- Refers to the weight of the weight of the roof structure itself and any permanent functional element.
The Live Load- Includes element such as human occupant, rain, maintenance equipment and other items of a transient nature.

Component of eco roof assert that these systems lightweight generally requires little additional load bearing capacity from most buildings structural systems, and in some cases may be installed on existing buildings with no structural modification.

The green roofing system manufacturers that suggest that extensive landscape systems need not be heavier than gravel covering used on some roofs. According o Kolb’s article in Anthos, a German are covered with gravel (approximately 5cm), which has a load about 100 kg / m2. Using this load as guideline for an extensive system, Kolb suggests that many gravel roofs might be greened, without additional load reserves.
(Source:http://www.sustainable-communities.agsci.ubc.ca/thesis/kp-6.pdf)

c) WIND

According to D. Nigel and K. Noel (2004) in their book “Planting Green Roof and Living Walls”, structures on roofs have to withstand high wind uplift because of their exposed position. This pressure varies across the surface of a flat roof, being relatively low in centre and at its most extreme near the edges and corners.

The layer of a green roof are therefore vulnerable o wind shear, particularly if the waterproofing layer is not bonded to the roof beneath and the green roof itself is acting as ballast to hold it down (D. Nigel and K. Noel, 2004).



Selecting Plant And Other Roof Garden Element.

(Source:http://www.sustainable-communities.agsci.ubc.ca/thesis/kp-6.pdf)

Nevertheless, a strip of gravel, stones or pavers around the edge of the roof and used vegetation barriers, preventing damage by plants to the edges of the roof where the waterproofing layer rises above the surface of the growing medium.

d) IRRIGATION

According to D. Nigel and K. Noel (2004), it has four main irrigation methods are used on green roofs that is:-

1. Surface spray with traditional systems. These are wasteful of water and can also encourage surface rooting which is vulnerable to extreme temperatures and moisture stress.

2. Drip and tube systems. These can either be pegged to the surface or buried in the substrate.

3. Capillary systems. Porous mats deliver water to the base of the substrate and are ideal for shallower a system, that is 20cm or less.

4. Standing water systems. These systems maintain a layer of water at the base of the roof.



Typical Irrigation For Roof Garden.

(Source:http://www.sustainable-communities.agsci.ubc.ca/thesis/kp-6.pdf)

GREEN ROOF CONSTRUCTION

The main function of the components or layers of green roof are include weatherproofing of the roof, protecting the roof surface from root penetration and damage, drainage, and the support and growth of the vegetation layer.



Section of Typical Extensive Green Roof Component.

(Source: D. Nigel and K. Noel, (2004), “Planting Green Roof and Living Walls”, Timber Press Inc, Portland, Oregon, USA.)-Page 65



Section of Typical Intensive Green Roof Component.

Source : (http://www.greenroofs.com/)

a) WEATHERPROOF MEMBRANE

Basically, there are 3 types of membrane we are using know that are the built-up roof (most commonly encountered and are composed of the familiar bitumen / asphalt roofing felt or bitumized fabrics), single-ply membrane (rolled sheets of inorganic or synthetic rubber material that are overlapped at the joints and sealed with heat, in the case of thermoplastic materials such as PVC) and the fluid-applied membrane (available in hot or cold liquid form that is sprayed or painted on to the surface of the roof and forms a complete seal when set, eliminating the problem of joints).

An effective waterproof seal to the roof is an essential prerequisite for all green roofs, and the importance of making sure this is effective and durable cannot be overstated (D. Nigel and K. Noel, 2004).

b) ROOT PROTECTION BARRIER

If the membrane on a roof upon which a green roof is to be installed contains bitumen, asphalt or any other organic material, it is crucial that a continuous separation is maintain between the membrane and the plant layer because the membrane will be susceptible to root penetration and the activity of micro-organisms- these organic oil based materials are not root proof. If the roof is not completely flat, then any pockets off collecting water can also form he basis of plant growth on a roof – again there be protection from roof damage (D. Nigel and K. Noel, 2004).

Balancing act of costs and benefits are main ecologist issues if we are talking about root protection barrier. Meanwhile some of commercial systems are based upon plastic base plate or metal because that form are a complete underlying structure to the green roof and isolate and raise the green roof completely from the underlying roof structure.

The membrane sheets are welded together to form a complete seal -it is essential that the welding is effective because any gaps or weaknesses will be exploited by the plant roots (D. Nigel and K. Noel, 2004).

c) DRAINAGE LAYER

Proper drainage is an importance thing when installing the roof garden. To maintain the drainage we should look to a several reason, which is: the protection of waterproof of roof membrane, precipitation falling onto a green roof and green roofs turn our normal interpretation of rainfall runoff on its head.

Drainage can be achieved in several ways. These techniques relate mainly to flat or very slightly sloping roofs. Where there is a more definite slope, which is, 5o or greater, drainage may effective without specific drainage layers. Combining a drainage layer with a water storage layer below it not only further reduces runoff compared to roof greening systems without such layer, by 11% to 17%, but acts as a reservoir for plants to draw upon in dry weather (D. Nigel and K. Noel, 2004).

The main types of drainage material are granular material (Coarse granular materials such as gravel, stone chips, broken clay tiles, scoria (lava rock), pumice, expanded shale or expanded clay granules, contain large amount of air or pore space between them when packed together in a layer or space), porous mats ( which operate similar way to horticultural capillary matting, act like sponges, absorbing water into their structure), and lightweight plastic or polystyrene drainage modules ( these modules vary tremendously In design and appearance and most sheets are thinner than 25mm).

Irrigation Lines Are Run Through Channels.

( Source : www.greentechitm.com )

A new designed of drainage medium are stronger, easily handled and cut, very lightweight drainage layer for roof gardens and planters of all kinds. Below grade, it protected from ultra violet light, it is permanent and highly efficient drainage medium (O. Theodore, 1999).

d) GROWING MEDIUM OR SUBSTRATE

The ideal substrate has to achieve the seemingly miraculous combination of being highly efficient at absorbing and retaining water while at the same time having free-draining properties. Substrate should be able to provide anchorage for the plants of the green roof. The ideal growing medium will comprise 30-40% substrate and 60-70% pore space. This will ensure good moisture retention capacity as well as aeration to the roots of the plants. If the pore space is saturated on along term basis, that is, continuously less than 15% of the substrate containing air filled pore space, then poor plant growth will result (D. Nigel and K. Noel, 2004).

For plant growth artificial soils can be superior to many natural soils provided they ate tailored for the specific type of vegetation they are to support. Artificially produced materials that have been used include vermiculite and perlite – both forms of heated and expanded mineral formed into granules. These are both extremely lightweight but it also have disadvantages in that they must be mixed with other materials because they cannot store nutrients and water and the particles of vermiculite tend to collapse aver time (D. Nigel and K. Noel, 2004).

Some Materials Used As A Basis For Green Roof Substrates.

Natural Minerals
1) Sand
2) Lava (scoria) and Pumice
3) Gravel

Artificial Minerals
1) Perlite
2) Vermiculite
3) Light expanded clay granules (LECA) Expanded shale
4) Rockwool

Recycled Materials
1) Crushed clay tiles, brick rubble
2) Crushed concrete
3) Subsoil

e) THE ADVANTAGES OF THE ROOF GARDEN SYSTEMS

System Provide Drainage and Root-Zone Airflow.

( Source : www.greentechitm.com )

1) Drainage Design - Water flows gravitationally through the modular system to the waterproofing layer and out to the roof drains.

2) Protection- The network of modules provides protection of the roof membrane during construction and maintenance activity from mechanical damage.

3) Weight- Eliminates gravel drainage medium typical of traditional intensive gardens. This is significant weight and labor savings.

4) Appropriate Soils- Each module can contain a totally distinct plant media thereby allowing the landscape architect maximum flexibility in the selection of plants.

5) Environment- Airflow beneath the root zone through the pallet channels develops deeper root structure and healthier plants.

6) Roof Membrane Repair- If there is leak in the roof membrane; modules can be easily removed and replaced later after leak fixed with minimal disruption to the garden.

7) Flexibility- The garden can be built off site and installed quickly upon completion of roof.

( Source : www.greentechitm.com )

f) PROBLEMS TO CONSTRUCT THE GREEN ROOF IN MALAYSIA

The problems to construct the green roof can be divided into 4 that are:

1) People Thinking

Nowadays, in Malaysia the green roof concept not very famous or familiar with people in this country. The green roof is a new phenomenon that we start to learned. Unfortunately, people still weird to talk about roof garden and stick with idea garden only can provide / develop at ground level.

2) Promotion

That is because lack of knowledge about green roof and lack of promotion to design our roof. However green roof are specified by professional with limited plant knowledge, whether they be landscape architect or horticulturist. Many of landscape architect in Malaysia today not really knows about green roof and they can’t propose green roof into their design.
3) Budget

To built a green roof basically we should have a lot of money and the budget is the main constrain to built the green roof. The planting green roof is often the most neglected aspect of the whole installation process. This may be result of budget limitations.

4) Law And Regulation

Malaysia have their own guideline to built green roof but the guideline not very completely show the importance of green roof as part as the way to control Urban Heat Island (UHI). The statement in that guideline only based on design of roof top garden and no explanation the importance to built green roof.

5) Policy

Government should give subsidize to encourage the building owner to built roof top garden on their building.