Components of Green Roof Design

Components of Green Roof Design

by Srinivas on December 21, 2010 0 comments

Components of Green Roof Design.

The components of the different types of green roof designs are the same. They differ only in the depth of the planted material and the specific design applied for different kind of projects. The components of the green roof designs are-

1) Vegetation

The plants need proper growth environment and if proper conditions are provided any plant can be grown on a roof. The limitations for the vegetation to be used are the climate; design or the structure; the money required for maintenance and of course the distinct imagination of the green roof designer. The green roof designs are usually lightweight and made up of a special form of ground cover that can grow even in a thin layer of soil with the minimum maintenance. The most popular form ground cover used in North America for the green roofs are sedum, which are herbaceous plants. The other common plants used are shallow-rooting grasses and wild flower plants. Sometimes, the green roof plants lose their leaves and become dormant.

2) Planting medium

The planting medium is not just plain soil, but it is synthetically produced clay with extra and specific mineral content, which are essential for plant growth. The synthetically produced clay is not as heavy as the normal soil and is the most appropriate planting medium because of its typical ultra-lightweight quality. The most common form of expanded clay is “Perlite”. It is widely used in green roof models and also in nursery plants. The recipes of different types of planting medium are commercially available. The total mass of the dry planting medium mixtures range from 400 kg/ meter cube to 900 kg/ meter cube. The water absorbencies of these dry planting medium mixtures range from 20-200 % by weight. In a few rooftop gardens, which employ high maintenance, soil is the planting medium used.

3) Filter layer

The filter layer lies in between the drain layer and the planting media. The filter layer permits water to flow through and retains the planting medium too. It also works as a barrier of the roots. The filter layer is made up of a double layer of unwoven geotextile. One of the layers of the filter layer can be treated with a mild root inhibitor like copper or an herbicide. Sometimes even filter fabric can be used in the green roof to prevent erosion on the upper surface of the planting medium.

4) Containment

The containment is actually the plant containers used in the modular systems. In the non-modular systems the drain layer supports the planting medium. The planting medium is held at the marginal areas by plastic or metal barriers, but most of the times the planting medium is contained by the roof parapet.

5) Drain layer

The drain layer lies between the planting medium and roof membrane. The water can flow through this layer through the green roof and ultimately to the drainage system of the building. In a few systems a layer of expanded clay is used, but most of the modern green roof designers use a corrugated plastic drain mat. This drain mat is specially designed like an egg carton or a landscape paver. The thickness of the drain layer is 20 mm. A thicker drain layer can also be used for additional insulation and restriction of the roots.

6) Protective Layer

The roof needs protection during the green roof installation and also from the affects of fertilizers and root penetrations. This roof protection is provided by a protective layer. This protective layer of the roofs is a slab made up of light weight concrete. Other protective layers in wide use are rigid insulation sheets, plastic sheets, copper foil or a combination of these layers. The selection of the appropriate protective layer depends on the structure and design of the green roof. There are a few green roof systems that do need a protective layer at all.

7) Insulation

The vegetation along with the planted medium and the different layers on the roof provide a good insulation and thus obviate the need of surplus insulation in warm and dry climates. Still the necessity of additional insulation cannot be ignored in certain building codes irrespective of the type of green roof designs beings used.

Water Proofing

Single-Ply membranes are commonly used in the green roof designs for waterproofing. The single-ply membranes are easy to use and also cost effective so most of the green roof designers prefer the singly-ply membranes for waterproofing.

9) Irrigation

The watering systems used in the green roof designs are a combination of passive irrigation techniques and other active constituents. The passive irrigation techniques used are rain water storage techniques. Rain water is absorbed by the drain layer, which in turn is absorbed by the planting medium and the excess water is drained off. The water storage medium like polypropylene filter mat is fixed directly under the planting medium. This mat is specially designed and acts like a sponge. Some green roof companies use small reservoirs in the drain mat. These reservoirs are filled with expanded clay till the layer of the planting medium. Irrigation is essential if plants needing excessive water are used, but if drought-tolerant plants or plants that need a minimum quantity of water like a wide variety of cactus are used in the green roof models then irrigation is not essential. The green roof models that use sedums do not need any special irrigation facilities.

by Srinivas on December 21, 2010 0 comments

Components of Green Roof Design.

The components of the different types of green roof designs are the same. They differ only in the depth of the planted material and the specific design applied for different kind of projects. The components of the green roof designs are-

1) Vegetation

The plants need proper growth environment and if proper conditions are provided any plant can be grown on a roof. The limitations for the vegetation to be used are the climate; design or the structure; the money required for maintenance and of course the distinct imagination of the green roof designer. The green roof designs are usually lightweight and made up of a special form of ground cover that can grow even in a thin layer of soil with the minimum maintenance. The most popular form ground cover used in North America for the green roofs are sedum, which are herbaceous plants. The other common plants used are shallow-rooting grasses and wild flower plants. Sometimes, the green roof plants lose their leaves and become dormant.

2) Planting medium

The planting medium is not just plain soil, but it is synthetically produced clay with extra and specific mineral content, which are essential for plant growth. The synthetically produced clay is not as heavy as the normal soil and is the most appropriate planting medium because of its typical ultra-lightweight quality. The most common form of expanded clay is “Perlite”. It is widely used in green roof models and also in nursery plants. The recipes of different types of planting medium are commercially available. The total mass of the dry planting medium mixtures range from 400 kg/ meter cube to 900 kg/ meter cube. The water absorbencies of these dry planting medium mixtures range from 20-200 % by weight. In a few rooftop gardens, which employ high maintenance, soil is the planting medium used.

Components of Green Roof Design

3) Filter layer

The filter layer lies in between the drain layer and the planting media. The filter layer permits water to flow through and retains the planting medium too. It also works as a barrier of the roots. The filter layer is made up of a double layer of unwoven geotextile. One of the layers of the filter layer can be treated with a mild root inhibitor like copper or an herbicide. Sometimes even filter fabric can be used in the green roof to prevent erosion on the upper surface of the planting medium.

4) Containment

The containment is actually the plant containers used in the modular systems. In the non-modular systems the drain layer supports the planting medium. The planting medium is held at the marginal areas by plastic or metal barriers, but most of the times the planting medium is contained by the roof parapet.

5) Drain layer

The drain layer lies between the planting medium and roof membrane. The water can flow through this layer through the green roof and ultimately to the drainage system of the building. In a few systems a layer of expanded clay is used, but most of the modern green roof designers use a corrugated plastic drain mat. This drain mat is specially designed like an egg carton or a landscape paver. The thickness of the drain layer is 20 mm. A thicker drain layer can also be used for additional insulation and restriction of the roots.

6) Protective Layer

The roof needs protection during the green roof installation and also from the affects of fertilizers and root penetrations. This roof protection is provided by a protective layer. This protective layer of the roofs is a slab made up of light weight concrete. Other protective layers in wide use are rigid insulation sheets, plastic sheets, copper foil or a combination of these layers. The selection of the appropriate protective layer depends on the structure and design of the green roof. There are a few green roof systems that do need a protective layer at all.

7) Insulation

The vegetation along with the planted medium and the different layers on the roof provide a good insulation and thus obviate the need of surplus insulation in warm and dry climates. Still the necessity of additional insulation cannot be ignored in certain building codes irrespective of the type of green roof designs beings used.

Water Proofing

Single-Ply membranes are commonly used in the green roof designs for waterproofing. The single-ply membranes are easy to use and also cost effective so most of the green roof designers prefer the singly-ply membranes for waterproofing.

9) Irrigation

The watering systems used in the green roof designs are a combination of passive irrigation techniques and other active constituents. The passive irrigation techniques used are rain water storage techniques. Rain water is absorbed by the drain layer, which in turn is absorbed by the planting medium and the excess water is drained off. The water storage medium like polypropylene filter mat is fixed directly under the planting medium. This mat is specially designed and acts like a sponge. Some green roof companies use small reservoirs in the drain mat. These reservoirs are filled with expanded clay till the layer of the planting medium. Irrigation is essential if plants needing excessive water are used, but if drought-tolerant plants or plants that need a minimum quantity of water like a wide variety of cactus are used in the green roof models then irrigation is not essential. The green roof models that use sedums do not need any special irrigation facilities.


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