All About Green Roofs

A general overview of green roofs including the different types of green roofs, the anatomy of a green roof, their environmental and financial benefits as well as how to go about implementing a green roof for your home.

A green roof is commonly understood as vegetative cover of a roof and is seen as an aesthetically pleasing and ecologically sound feature of a home, factory or any other building. In its basic sense, a green roof is a roof covered with vegetation that feeds of rainwater and is equipped with special impermeable membranes and drainage layers to prevent overflow and leakage. Green roofs expand the vegetative cover of a property and therefore contribute to a more stable micro-climate. Instead of only lawns and gardens providing green surfaces, roofs can be covered in vegetation effectively increasing the rainwater retention capacity of a property.

Types of Green Roofs

There are commonly two types of green roofs – intensive and extensive green roofs. Both types of roofs serve different purposes and are applicable to different structures. The type of green roof a property owner chooses to implement depends on the type of building and the expectations of the owner.

Intensive Green Roofs

An intensive green roof refers to a green roof that contains greater and more diverse vegetative cover and can include pathways and relaxation areas for visitors. Intensive green roofs may contain various grasses, shrubs, flowers and even crops and trees. The soil depth is usually 15cm or deeper and the payload is around 730kg per square meter. An intensive green roof typically requires regular maintenance. This means that green roofs are usually found on strong load bearing roofs that are easily accessible for maintenance and perhaps to the public or company staff for recreational and relaxation purposes. Intensive green roofs are fast becoming a popular feature of modern ecological urban architecture as it is an effective means of adding green space to a city without compromising the economic and social purposes of existing urban structures. In other words, a mix commercial zone can retain all its commercial space while adding intensive green roofs to its properties effectively expanding the size and use of their properties as well as providing a host of other benefits associated with green roofs.

Extensive green roof on the roof at the bus terminal in Zvolen, Slovakia serves as a relaxation zone accessible to the public (project realized by our partner firm Vodales s.r.o.)

 

Extensive Green Roofs

An extensive green roof refers to a green roof with a limited amount of plant diversity and soil depth. Typically, an extensive green roof depth ranges from 8 – 15 cm in depth and contains mainly grasses and shrubs and carries a load up to 240kg per square meter. This means that extensive green roofs require minimal maintenance compared to their counterparts and serve more of an ecological and aesthetic purpose instead of a recreational purpose. Such roofs are best suited for family homes or retrofitted to existing structures that may not be able to withstand the load of an intensive green roof.

An intensive green roof on a library terrace is also accessible to school children and staff.

 

Anatomy of a Green Roof

 

The above diagram shows the basic anatomy of a green roof – applicable to both intensive and extensive green roofs. While some variations exist between different contractors, all roofs must contain certain features to assure functionality and prevent failure. Since this is part of the DIY section, we will mainly focus on extensive green roofs as these are the most applicable for homes. Key points to consider when taking on a green roof project are:

  1. Structural stability – in a retrofit project, a structural engineer should be hired to assess the load bearing capacity of your roof prior to construction. If you are building a new home, the architects should account for the extra weight of the green roof into the project plan.
  2. Waterproofing membrane – in addition to the existing roof membrane or surface, a waterproofing membrane is an absolute essential to prevent leaks in the roof which can cause gradual damages to the roof structure and the home. There are numerous types of waterproofing membranes available on the market. It is best to get advice from suppliers based on the type of existing roof.
  3. Root barrier – prevents vegetation roots from penetrating the waterproofing membrane and causing leaks in the roof. On extensive roofs, this can be considered more of a precautionary measure since the vegetation does not typically have deep growing roots.
  4. Filter and drainage layer – filters prevent sedimentation from seeping into the drainage layer resulting in cleaner rainwater runoff from the roof and retaining sedimentation on the roof. A properly installed drainage layer prevents the green roof from oversaturation of water.
  5. Growing substrate – substrates for green roofs differ from regular substrate to meet the special conditions that come with having a vegetative surface on a roof. First, substrate needs to be low bulk to keep weight low. It should also be relatively permeable to prevent excess saturation yet should retain enough water to support plant growth. Additionally, high quality substrate has a finely balanced nutrient content to prevent excessive plant growth. The substrate you choose depends on numerous factors but is mainly determined by the structural rigidity of your roof.
  6. Vegetation – extensive green roofs usually contain grasses and sedums hence their relatively shallow substrates. Extensive green roofs are not used for growing vegetables nor are they intended to be walked on except for maintenance.  

Benefits of a Green Roof

There are numerous benefits to be gained by installing green roofs on your property ranging from aesthetic to ecological and financial. Let us explore each of the benefits in more detail.

Aesthetically, green roofs offer a piece of mind by adding more nature back to an urban environment. With increased competition for landuse, urban settings often lack green space; green roofs bring nature back to the city or the urban home without encroaching on functional space. Compare a green roof with a roof made of steel, shingles or other conventional materials; most likely the green roof is the much more aesthetically pleasing option while fulfilling many ecological benefits. Additionally, due to their insulating properties, green roofs reduce ambient noise.

Perhaps the greatest advantage offered by green roofs is their environmental benefits. These are:

  1. Reduce the heat island effect – green roofs retain rainwater which is used by vegetation. When plants transpire they naturally have a cooling effect on the areas micro-climate. Essentially green roofs promote evapotranspiration instead of run-off.
  2. Stormwater management – green roofs reduce rainwater run-off therefore reduce the risk of flooding during intense precipitation by delaying the peak flow rate. They further reduce the burden on urban sewage systems which, when overloaded can lead to sewage being released with stormwater into water bodies.
  3. Improved water quality – green surfaces generally clean water impurities before the water makes its way into streams and rivers.
  4. Improved air quality – vegetation on green roofs is a natural filter of air; water during photosynthesis creates oxygen.
  5. Carbon sequestration – photosynthesis requires solar radiation, carbon in the atmosphere and water. Plants sequester carbon which produces biomass.
  6. Increased biodiversity – a conventional roof is void of life. Green roofs grow a variety of suitable grasses and shrubs or even crops and trees in the case of an intensive green roof. Green roofs increase much needed biodiversity in urban settings.
  7. Habitat & sustenance for urban bird life and other organisms – the biodiversity of green roofs attracts birdlife and insects adding green appeal to a concrete jungle.

 

Thermal regulation properties of green roofs vs conventional roofs.

Green roofs also carry with them a host of financial benefits which in the long run, bring a greater return on investment over conventional roofing systems.

  1. Reduce energy use – green roofs effectively cut your air conditioning and heating bills by absorbing solar radiation in the summer and providing insulation in the winter.
  2. Reduce stormwater management fee – in many cities around the world, stormwater management is a paid for service based on the average annual volume of rainwater that is drained from a property. By reducing or stopping runoff with green roofs and other water retention measures, property owners can reduce their stormwater management fees.
  3. Improve the roofing membranes life span – green roofs provide protection against physical, chemical and biological damage. They protect the roof from UV rays and thus green roofs have a much longer lifespan than conventional roofs when properly maintained.
  4. Benefit from rebates or grants – some government programs offer rebates and grants to property owners who install green roofs on their buildings. Find out whether your local government provides such incentives for installing a green roof.
  5. Increase property value – with the growing trend of green architecture, green roofs may add value to your property. Combined reduced energy costs and increased lifespan of your roof has positive effects on property values.

With the above listed financial benefits, green roofs provide more effective long-term financial practicality over conventional roofing systems plus their environmental benefits and aesthetic appeal alone are worth the investment.

Green Roofs within the Global Rehydration Objective

Green roofs are fully in line with the numerous landscape regeneration and green architecture initiatives taking place around the world from New York City’s green roof ambitions to Initiative 20x20 to Mexico City’s green pillars, Berlin and beyond. Green roofs stabilize the micro-climate of an urban area by strengthening the thermoregulation function of an urban landscape. Green roofs do this in two ways, they retain rainwater where it falls, and they enable evapotranspiration.

Daily distribution of solar energy on a dehydrated vs hydrated landscape.

Water is planet earth’s main thermoregulation agent. Green roofs contribute to climate stability by capturing rainwater on the roof via its vegetation and soil cover. Rainwater retained by a roof’s vegetation enables photosynthesis causing vegetation to transpire. Combined with evaporation, evapotranspiration is a natural air-conditioning system for the surrounding micro-climate. A barren landscape without vegetation cover (as seen in the picture on the left) does not allow much evapotranspiration since there is very little water in the landscape. As a result, solar radiation is converted into sensible heat near the earth’s surface. This is commonly referred to as the heat island effect experienced during summer month’s by most urban centers around the world. Green roofs not only add aesthetic appeal, financial benefits and a host of practical environmental benefits such as flooding prevention but they are a key feature of combatting extreme weather and climate change.

Green roofs augment the resiliency of a landscape by mimicking more closely the natural landscape before its alteration by human activity. In a natural landscape, the small water cycle functions perpetually through the constant return of water back to the water cycle via evapotranspiration. Green roofs return urban centers closer to this process again increasing evapotranspiration instead of run-off. While a few green roofs will not make a drastic change to the climate of a major city; ongoing research is investigating the critical mass required for green space in urban centers to positively impact urban climate on a large scale.

How to Implement your own Green Roof  

There are numerous ways one can go about implementing a green roof on their property. The factors determining who implements a green roof include one’s skillset and know-how, time, access to tools and equipment, size of property, complexity of design, etc. You may decide to complete almost the entire project yourself or you may leave part of the work to a contractor and part of it for yourself.

There are two key components that require expert guidance when implementing a green roof. One component of a green roof installation that absolutely requires expert advice is measuring the structural rigidity of the building in question. A structural engineer will need to assess the strength and load bearing capacity of the roof before a green roof installation can begin. Another step that should be left to an expert is the proper water proofing of the roof. Unless you are absolutely confident in installing the water proofing membrane, having a reputable company install the waterproofing membrane can save headaches and costs in the future by avoiding a leaking green roof which can also negatively impact the structural stability if left unattended. Other than these two components of a green roof installation, the other steps can be taken on by homeowners who like getting their hands dirty.

Another option is to have the entire project implemented by a reputable landscaping or green roof company. The easiest option is to ask friends, family and neighbors if they know of any reputable contractors in your area. In the USA, another option is to search the various industry organizations such as the American Association of Landscape Architects, United States Green Building Council, Associated Builders and Contractors and others for certified contractors in the green roof and architecture industry. With the internet at our fingertips, searching for contractors is easier than ever before. Just make sure to review their references in order to ensure that the job will be completed properly.

If the search for contractors sounds daunting, then you can wait for the launch of our very own Rehydration Portal, where we bring together investors, know-how, contractors and other experts to roll out the rehydration of the earth’s continents on a global scale. Through this rehydration portal, you will be able to find a reputable contractor within your area who will help you implement your green roof of your dreams.   

Water is planet earth’s main thermoregulation agent. Green roofs contribute to climate stability by capturing rainwater on the roof via its vegetation and soil cover. Rainwater retained by a roof’s vegetation enables photosynthesis causing vegetation to transpire. Combined with evaporation, evapotranspiration is a natural air-conditioning system for the surrounding micro-climate. A barren landscape without vegetation cover (as seen in the picture on the left) does not allow much evapotranspiration since there is very little water in the landscape. As a result, solar radiation is converted into sensible heat near the earth’s surface. This is commonly referred to as the heat island effect experienced during summer month’s by most urban centers around the world. Green roofs not only add aesthetic appeal, financial benefits and a host of practical environmental benefits such as flooding prevention but they are a key feature of combatting extreme weather and climate change.

Green roofs augment the resiliency of a landscape by mimicking more closely the natural landscape before its alteration by human activity. In a natural landscape, the small water cycle functions perpetually through the constant return of water back to the water cycle via evapotranspiration. Green roofs return urban centers closer to this process again increasing evapotranspiration instead of run-off. While a few green roofs will not make a drastic change to the climate of a major city; ongoing research is investigating the critical mass required for green space in urban centers to positively impact urban climate on a large scale.

How to Implement your own Green Roof  

There are numerous ways one can go about implementing a green roof on their property. The factors determining who implements a green roof include one’s skillset and know-how, time, access to tools and equipment, size of property, complexity of design, etc. You may decide to complete almost the entire project yourself or you may leave part of the work to a contractor and part of it for yourself.

There are two key components that require expert guidance when implementing a green roof. One component of a green roof installation that absolutely requires expert advice is measuring the structural rigidity of the building in question. A structural engineer will need to assess the strength and load bearing capacity of the roof before a green roof installation can begin. Another step that should be left to an expert is the proper water proofing of the roof. Unless you are absolutely confident in installing the water proofing membrane, having a reputable company install the waterproofing membrane can save headaches and costs in the future by avoiding a leaking green roof which can also negatively impact the structural stability if left unattended. Other than these two components of a green roof installation, the other steps can be taken on by homeowners who like getting their hands dirty.

Another option is to have the entire project implemented by a reputable landscaping or green roof company. The easiest option is to ask friends, family and neighbors if they know of any reputable contractors in your area. In the USA, another option is to search the various industry organizations such as the American Association of Landscape Architects, United States Green Building Council, Associated Builders and Contractors and others for certified contractors in the green roof and architecture industry. With the internet at our fingertips, searching for contractors is easier than ever before. Just make sure to review their references in order to ensure that the job will be completed properly.

If the search for contractors sounds daunting, then you can wait for the launch of our very own Rehydration Portal, where we bring together investors, know-how, contractors and other experts to roll out the rehydration of the earth’s continents on a global scale. Through this rehydration portal, you will be able to find a reputable contractor within your area who will help you implement your green roof of your dreams.