A green roof can provide a cooling effect on the immediate surroundings, benefiting both the building and the area. Also, there is an insulating effect by the layer of soil, if used. Green roofs, if implemented widely in a city, could help reduce the heat island effect.[verification needed]
However, they typically require a stronger structure, particularly if soil is used. Thus any environmental advantages may be offset by the greater embedded energy of the structure. The insulating effect can be achieved more cheaply by other means.[verification needed] See Insulation. However, other forms of roof insulation will not have the same cooling effect on the immediate surroundings.
Literature Review[edit | edit source]
Living roof basics[edit | edit source]
The basic components of green roof systems are waterproofing, soil and plants. It really is that simple. The combination of these material is easy and the success of all living roofs depends on the types of plants used and an understanding of how these combined materials will work. An understanding of the type of environment the roof will be located in is also important for the success of any living roof. For example here in Humboldt County earthquakes pose a risk as well as a high precipitation level in the fall and winter months, however in the spring and summer months there is little to no rain fall. Design should account for earthquakes and the forces it will create on the building as well as any irrigation or drainage components that will function during both during the wet season and dry season. These however are design features that should be asked when building the structural support and housing unit the living roof will be placed on top of before and during construction of both the roof and the house or structures for the roof. For the purpose of our project we were only asked to concern ourselves with the construction of the roof itself because the farm would be responsible for the hutch or housing unit and the structural support. This means we focused on the weather aspect of design for the roof. Living roofs are that simple especially for small designs. Living roofs are becoming increasingly popular in North America and are starting to show themselves in large scale industrial buildings. The design and construction of those types of roofs are a little more complex and a lot more labor intensive, but the end result is worth the effort
Living roof concerns[edit | edit source]
A main concern regarding living roofs revolves around the types of vegetation that is being used because the performance of the living roof is the plant communities. Concerns regarding the plant communities on living roofs deal with weather factors such as wind stress and over exposure to the sun, however in the literature the main focus has been on wind stress because plants are not generally accustomed to the heights that roofs generally are. There has been some practice of using native plant species because they are generally most accustomed to the region the roof is. However, in some of the literature discusses native plants not working on extensive living roofs because of the shallow soil depth generally found on extensive living roofs.This then means that not only is wind stress the main factor in determining the types of flora being used but that the rooftop itself is challenging for the survival of plants.
Another more recent concern that has appeared during the increased popularity of living roofs is water-quality of the storm water runoff from living roofs. The literature suggestes that living roofs may act as another source surface-water pollution primarily because of the nutrient content found in the growing medium and soil used. To combat this we tried to use soil and growing mediums that not only would maintain the health of the plants but that were already found on the farm. We went with a perlite and coco peat combination.
Types of Living Roofs[edit | edit source]
In the world that is living roofs there are generally two types of designs. They are intensive and extensive. More recently there has been the inclusion of a hybrid living roof that is a combination of these two types called semi-extensive.
Intensive[edit | edit source]
Intensive living roofs are found on industrial building such as parking garages or other public buildings usually heavily trafficked by humans. Intensive living roofs have a very high plant diversity because these roofs have the ability to provide very deep soil potential for these various plant communities. Intensive living roofs may be viewed as actual gardens on roof structures not just because of the plant diversity but because those plants are maintained on an individual basis similar to what is found on ground level. This also means that intensive living roofs have irrigation systems built into the living roof system. The combination of these two things makes intensive living roofs very high maintenance physically and monetarily.
- Here is a useful advantages and disadvantages look at intensive living roofs that may express the concept a little easier.
|Diversity of plants||Greater weight load on roof|
|Good insulation properties||Need irrigation and drainage system|
|Simulate wildlife garden||Greater weight load on roof|
|Attractive aesthetically||Need irrigation and drainage system|
|Accessable/recreation||High maintenance and cost|
|Longer membrane life||High maintenance and cost|
|Storm water retention capability||More complex|
Extensive[edit | edit source]
Extensive living roofs are low maintenance roofs because this design type is used most often used with lightweight and low height buildings. The soils in extensive living roofs are generally shallow.Especially much shallower than intensive living roofs because the plant communities in extensive living roofs tend to be self-generative plants or types of plants that can survive in some sort of "desert" like environment.Some types of plants may include shrubs, grasses, mosses, and indigenous plant species.
- Here is a useful advantages and disadvantages look at extensive living roofs that may express the concept a little easier.
|Lightweight. Generally no reinforcement||Less energy efficient|
|Suitable for large areas||Less storm water retention benefits|
|Roof slope 0degrees-30degrees||Limited choice of plants|
|Long life and low maintenance||Not accessible for recreation or other uses|
|No need for irrigation or specialized drainage system.||Unattractive usually in the winter season|
|Vegetation can grow spontaneously|
Semi-Extensive[edit | edit source]
There is more information on semi-extensive living roofs out there, but the main idea behind the design is that it is low maintenance like an extensive roof, but has deeper layers for growing medium like an intensive roof has. Meaning high diversity of plants with low-input.
Living roof design[edit | edit source]
The design of a living roof depends on the wants and needs of those requesting one for their home or industrial units. A living roof should be viewed as another artistic expression of self because they can be built, placed, and designed in a manner that expresses either the designer or the one inhabiting the structure. However, the one aspect of living roofs that generally has laid out plans or rules that should be followed are the different layering components of living roofs.
- Here is an example of generic layering usually found on industrial living roof systems. Some of these layers may be applicable to smaller scale roofs.
|Deck Layer||Is the foundation of a green roof and may be of concrete, wood, metal, plastic or a composite material|
|Leak Detection System (optional)||Leak detection systems are often installed above the deck layer to identify leaks, minimize leak damage through timely detection, and locate leak locations.|
|Waterproofing Layer||Very important to prevent water damage through the deck layer. This layer must be entirely waterproof and long lasting. Several waterproofing materials can be used, like thermoplastic membranes, elastomeric membranes, modified bitumen polyvinyl chloride (PVC), applied rubberized asphalt, built up bitumen and others. The waterproofing material may be loose laid or bonded, which is more recommended.|
|Insulation Layer(optional)||Usually located above, but sometimes below, the waterproofing layer. Its function is to increase the energy efficiency. Recommended for metal roofs|
|Root Barrier||Used to protect the waterproofing membrane from root penetration|
|Drainage Layer||Placed between the root barrier and the growing media to remove excess water from the vegetation root zone. Must consist of synthetic or inorganic materials. The thickness of the drainage layer type is an important design decision. For extensive green roof systems, the depth of the drainage layer usually varies from 0.25 to 1.5 inches thick and increases for intensive designs.|
|Filter Sheet||Consists in a "semi-permeable needled polypropylene filter fabric placed between the drainage layer and the growing media" in order to prevent the drainage layer to clog by the migration of some particles from the media into it. The filter sheet must allow the water migration into the drainage layer|
|Growing Media||Usually 3 to 6 inches deep and composed of approximately 70 to 80 percent lightweight inorganic materials like clays, pumice, scoria or other similar materials. The remaining media must not exceed 30 percent organic matter because it can transport nutrients into the runoff from the roof and clog the permeable filter sheet.|
|Plant Cover||It is the top layer and consists of plants that are non-native, slow-growing, shallow-rooted and perennial. The selected plants must be able to withstand harsh conditions at the roof surface. For drought periods it is recommended the installation of a watering system.|
Suggested projects[edit | edit source]
- Weigh up the environmental advantages and disadvantages of green roofs, comparing them with alternative designs.
Concerns[edit | edit source]
Lightweight green pergola roof[edit | edit source]
Pergolas can made of light wood slats, netting, cords, PVC pipe, etc. Care should be taken to provide adequate structural support, as luxuriantly growing vines can be quite heavy, and to insure that the roof remains accessible for maintenance. High winds or snow may also impose stresses.
Depending on species and situation, vines may take several years to achive full coverage. It may sometimes be advisable to plant two species for a few years - a fast-growing annual species to provide temporary shade while a slower-growing permanent species is getting established.
Pergolas can also be used as supports for other shading materials such as cloth, light wooden slats, cut vegetation, etc. Care should be taken in the selection and fastening of materials to prevent damage or injury in the event of high winds or other stressful conditions.
Notes[edit | edit source]
- Weiler, S.K. and Scholz-Barth. 2011. "Green rood system: A Guide to the Planning, Design, and Construction of Landscapes over Structure".
- Oberndorfer, Erica, Jeremy Lundholm, Brad Bass, Reid R. Coffman, Hitesh Doshi, Nigel Dunnett, Stuart Gaffin, Manfred Köhler, Karen K. Y. Liu, and Bradley Rowe. 2007. "Green Roofs as Urban Ecosystems: Ecological Structures, Functions, and Services. (Cover Story)." BioScience 57 (10): 823–33.
- Dunnett, Nigel, and Noel Kingsbury. Planting Green Roofs and Living Walls. Portland: Timber Press, 2008.
- Lazzarin, Renato M., Francesco Castellotti, and Filippo Busato. 2005. "Experimental Measurements and Numerical Modelling of a Green Roof." Energy and Buildings 37 (12): 1260–67.
- Peck, S. and M. Kuhn. 2003. Design Guidelines for Green Roofs (PDF) (22 pp, 551K). Canada Mortgage and Housing Corporation and the Ontario Association of Architects
- "Green Roof Systems: Intensive, Semi-Intensive, and Extensive.".Architect's Technical Reference. Accessed February 8, 2015. http://www.archtoolbox.com/materials-systems/site-landscape/green-roofs.html..
- "Hoffmann, G., Stack, R.C. and Wye, B.V. 2012. "Stormwater Management Guidebook".