Green roofs have many benefits, and that is the reason why they have started trending in Australia. Some people believe that green roofs are too expensive and that is why they haven’t installed them.
However, they can be affordable if you are adding to an extension or building. The cost guide below shows everything you need to know about green roofs.
How is a Green Roof built?
- A waterproof membrane can be constructed with different solid and liquid materials. Liquid materials include bitumen based membranes. It has a root barrier layer that inhibits roots from penetrating the membrane.
- Other green roofs contain an insulating layer. You might need to meet the BCA thermal regulations. Remember it is difficult to obtain the insulation value of green roofs in Australia.
- Green roofs have a drainage layer that pours out excess water.
- It has a filter fabric constructed with geo-textile material like fleece or a woven material.
- It has a growing medium made from 75-80% of the inorganic material. The organic material is about 20-25%. For proper drainage, there must be the inorganic material.
- It's top layer has vegetation. Extensive green gardens should have plants that are easy to maintain and their root system should be shallow. Additionally, you can allow taller plants in intensive green gardens if trees are the low growing medium.
What is the cost of a Green Roof?
The following are the costs you will incur when building a Green Roof in Australia.
- Council fee (inclusive of building permit and DA)
- Design Fees
- Licences for cranes and lifts
- Other additions such as furniture, paving or shade structures
- Rebuilding costs and demolition ( if retro-filing)
- Strengthening the steel roof costs $240m
- Strengthening a concrete ceiling above trafficable areas costs $450-$650m2
- Values of additional column is $2500 and $4500
- Waterproofing costs $100
- Cost of drainage and protection layers is around $100m2 and $500m2. But it depends on the depth of the growing medium that you use.
- Decking, paving and all kind of flooring can be $200-$400 per square metre.
- Edge restraints cost about $50 for every linear metre.
What is a Green Roof?
Any roof with vegetation growing on it is called a Green roof. You can let plants cover it fully or partially. There are two types of green roofs:
- The extensive Green roofs
- The intensive Green roofs
However, you can still build a Green roof that falls into the above categories.
Extensive Green roofs, on the other hand, have a shallow soil of 200mm thick. It weighs 60 and 200kg per square metre . You can plant plants that have a shallow root system on these roofs.
Such facilities include different types of plants with the shallow root system. If you want to choose the right Green roofs, you can get help from a landscaper who has experience in creating Green roofs.
The Intensive Green roofs, on the other hand, have a deeper soil than extensive green roofs. You should, therefore, build the roof so that it can bear the soil’s weight and that of plants. You can get an architectural designer to design your roof. Due to its weight and quality, an intensive green roof happens to be more costly than the latter.
You can add an extensive green roof to a metal or another lightweight roof. Intensive green roofs are supposed to be constructed on a flat concrete roof. You can build an extensive roof garden if you would like to build your roof as an entertainment area or as a patio. While an extensive roof can’t withstand the weight of traffic, it can provide your home with the following benefits.
- A thermal insulation
- A durable roof
- Acoustic insulation
- It reduces the intensity of storm water runoff
- It absorbs air pollutants
According to experts, intensive roof gardens are more beneficial than extensive roof gardens. As much as the cost may be a factor to consider, intensive roofs increase the value of your property. Apartment blocks that have intensive green roofs in Toronto Canada attract great rental rates by 15% more than apartments that have conventional roofing. The same thing happens in Europe.
How is a Green Roof constructed?
Green roofs can have up to seven layers.
You can make a waterproofing membrane from sheeting materials, solid materials and liquid materials like bitumen based membranes.
A green roof has a root barrier which inhibits roots from penetrating through the membrane.
If you want to meet the BCA thermal insulation regulations, you might need an insulating layer. Obtaining the insulation value of Green roofs in Australia is quite difficult.
The drainage layer is responsible for carrying excess water
The filter fabric has a geo-textile material like fleece.
Seventy-five to eighty percent of inorganic material makes the growing medium, while the inorganic material is 20-25%.
Its top layer comprises of vegetation. Extensive green gardens should have plants that are easy to maintain having a shallow root system.
If the growing medium is thick trees, the intensive green gardens can have tall plants. Soil depth determines the type of facilities you can use. You can use turf and shrubs if the growing medium is 250mm. Grow trees up to 5m height if the organic medium is one meter deep.
You need to note that all costs provided in this post are a rough guide. It can cost you more or less depending on ease of access or difficulty, your location, and other factors as well. To avoid walking on the roof, consider installing a drip irrigation system. You can get advice from irrigation system suppliers because they are familiar with green roofs.
You can also consider the costs of a landscape architect and a garden designer. If you are adding a home extension or building a new home, you might need to hire a landscape architect or a garden designer who is experienced in creating roof gardens. They can do the budget for you and design your roof. They can ensure that your builder who may have less experience with green roofs creates a long-lasting green roof.
As much as green roofs are new concepts in Australia, consider finding garden designers architects and other home improvement professionals who have experience in installing green roofs in Australia. Some city councils encourage Australians to install green roofs due to their environmental benefits.
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