Can I Put a Green Roof on My House
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If you have a flat roof on your home you may be wondering: can I put a green roof on my house? We look at the benefits of green roofing and which buildings it can work for.
What are the Benefits of a Green Roof?
Green roofs are one of the most telling signs that someone has chosen to make their home a sustainable place to live. Many people are sceptical about the ecological benefits of a green roof and whether they are a worthwhile investment. But, there are some genuine positives that a green roof can bring to your home:
They are perfect at absorbing direct heat from the sun, CO2 and up to 70% of the rain that falls on them.
Green roofs offer a good amount of insulation, but they are more suited to keeping homes cool in the summer rather than warm in the winter.
Another great benefit to installing a green roof is that it is a way of accounting for and replacing the ecological environment removed to construct the house.
This final benefit to installing a green roof is perhaps the most important. Green roofs are an easy thing to install and can greatly benefit the surrounding ecology of your home. Caring for our ecology and ensuring that our natural environments and habitats can survive is more important now than it ever has been. Therefore, by installing a green roof on your home, you can lend a helping hand.
A green roof is also an excellent way to soften your home's aesthetics, helping it blend in with its natural surroundings. If you choose to install a green roof across the entirety of the top of your home, this will impact how you design the entire structure. The impact will stretch through your home's construction, even affecting the foundations.
Of course, you do not need to install a green roof across the entirety of your roof. Even having a small planter installed can be a lovely touch and a step in the right direction. If you do not have access to your roof, you might consider green roof installation on an outhouse, shed or garage. You could even install an extensive system onto a new extension you are thinking of constructing.
Marrying the right systems and the right location will ensure zero negative aspects to your green roof. So, given that green roofs are all positive, a better question might be - which green roof system is most appropriate?
Types of Green Roof
Living roofs, grass roofs, sedum roofs - there are many different names for a green roof, and they all practically describe the same thing. There are, however, two main forms of green roofs that you can choose from.
Extensive green roofs
Extensive green roofs are the most popular of the two choices, given that they require very little maintenance aside from watering during dry spells. They are also very lightweight, making them the perfect fit for most buildings, whether existing or newly built.
Extensive green roofs generally have a shallower level of greenery, typically no taller than 8-10 cm, mainly created from grass, moss, small flowers and sedum. If you choose sedum blankets, they will need a growing medium, but it does not need to be deep. Of the extensive green roofs, sedum greenery is the most common due to its resilient and low maintenance plants.
Intensive green roofs
Intensive green roofs are designed to sustain much larger vegetation, such as large bushes or trees and many other species of plants. You may have heard them referred to as roof gardens, and they require a much deeper level of growing medium, such as soil, to help sustain the larger vegetation.
Intensive green roofs are typically not found on residential or domestic homes, being more common in commercial locations such as parks or gardens where people are expected to visit recreationally.
Given that intensive green roofs require a deeper level of growing medium, this will naturally add more weight, additionally loading the structure. Therefore, the building that will hold the green roof will need to be strong enough to support it. There will also need to be an irrigation system installed to sustain the vegetation. As the name might suggest, intensive green roofs require much more maintenance, similar to a typical garden.
Semi-extensive green roof
A semi-extensive roof is a mix of the two main forms, with a greater emphasis on the extensive roof system. The depth of the substrate level is larger than an extensive green roof, measuring between 10-20 cm. While this form of a green roof can support a wider range of plant life, it is not suitable for trees or shrubs.
Which is best?
The extensive green roof is the best choice for those who need a lightweight, easy to maintain roof garden that will add great aesthetics to their home. They are easy to install on almost any structure, adding great insulation during those warmer months and even adding sound protection.
Of course, if you prefer a wider variety of plant life on your green roof, then an intensive roof garden is the way to go. However, given that you will be growing a wider range of vegetation, this will mean a greater amount of attention will need to be paid to your roof garden.
If you choose to grow shrubs and trees, you will need to consider the strength of the structure supporting the green roof. You will also have to install any necessary irrigation to ensure that the environment you construct can be sustained.
How are Green Roofs Installed?
To install a green roof, the top of the building must not have a pitch angle over 30° once planted and preferably be flat. Before you begin laying down any substrate, you will need to lay a moisture-retention fleece layer. This layer will help with waterproofing, keeping any water within the substrate soil rather than pooling at the base where the membrane surface is.
You will also need an aqua drainage layer to remove any excess water from the soil. Of course, a good quality membrane will have its own leak prevention design already. However, what the membrane cannot do is prevent water vapour from entering the building. For this, you will need a vapour control layer.
This will prevent water vapour within the membrane layers of the green roof from condensation on the inside of the building's roof. Plastic root barrier mats will also be required to keep the plants' roots from damaging the structure.
Suitable plants for Green Roofs
Extensive green roofs
Given that creating an extensive green roof tends to be easier than intensive ones, requiring less maintenance, you will want to choose plants that can survive independently without needing too much attention. Pre grown species such as Sempervivum, Sedum, and general low-growing mosses are all great choices. Typical Sedum species that would work well in most green roofs include S. album, S. rupestre and Sedum acre. Delosperma is also a great choice for those who live in sunnier climes, where frost is scarce in the winter. You might also consider some species of Fern, such as Asplenium trichomanes or Polypodium. These species would suit dry, dark places such as rooftops that receive a lot of shade.
Intensive green roofs
The best vegetation for intensive green roofs are those that are drought tolerant. These species are capable of withstanding both sun and wind, making them perfect for larger roof gardens. They will most likely have silvery or greyish coloured leaves for reflecting harsh sunlight. They may also have fine hairs along with their leaves or stems for trapping moisture against the plant.
Semi-extensive green roofs
The best species for this mixed type of green roof are ornamental grasses or perennials. Species such as Achillea, Armeria, Dianthus or Stipa tenuissima would work the best. You may even consider planting some bulbs. Bulb species such as Allium or Muscari would probably work best.
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