A Guide to Green Roofs – Helping Buildings do more for the Environment
Green roofs are becoming an increasingly common site in both urban and rural areas of the UK. As a result, a significant proportion of the turf we produce eventually ends up on top of a building instead of on the ground, on everything from log stores and sheds through to schools and large office developments.
So what is all the fuss about and why would anyone want to line a roof with turf? And, given the weight of substrate, how is it even possible?
In this article, we’ll seek to answer these questions and more as we take a deep look into green roofs.
Insulation qualities
But before we get into the whys and hows, first a little history. Green roofs are not a new phenomenon and have long been utilised for their insulative properties. For centuries, green roofs have been used in Scandinavia and other cold countries to keep heat in a property, and in hot countries to keep heat out.
As well as this, green roofs have been popular in traditional building practices as a way to attenuating water and reducing run off to limit the possibility of flooding.
More recently, concerns about the decline of green spaces in urban environments, particularly in Germany and Switzerland, prompted a renewed interest in green roofs as a solution.
Now, with huge losses of biodiversity and the need to grow more plants to absorbed atmospheric carbon, they are once again being rightly lauded as an environmental solution and are being included in the designs of many new building developments.
Advantages of green roofs
We’ve heard the historical reasons why people used green roofs, but what are the modern-day benefits? As you may expect, these now tend to focus on sustainability and the environment, and how green roofs have a role in mitigating climate change and biodiversity loss. They include:
· Creating new habitat for plants, insects including pollinators, and even birds
· Absorbing greenhouse gases
· Absorbing air pollution and atmospheric dust particles
· Reducing the heat island effect in urban areas
· Reducing rainwater run off to mitigate flooding risk
There are, of course, other advantages to green roofs as well. As previously mentioned, they have very high insulative properties, helping to keep houses warm in winter and cool in summer, and they can reduce noise pollution from outside your home.
They add a protective layer on top of the structural part of a roof, protecting it from UV radiation and even mechanical damage, therefore extending its life. And they simply look good. Let’s not underestimate the wellbeing uplift achieved by increasing the number plants, animals, and green spaces in an environment. More green roofs means more happier, healthier humans!
What type of turf?
So, what type of turf is best for a green roof? This is a question we get asked a lot.
For this, we would recommend either our wildflower turf, our species rich turf, or our specially-designed Sedum Mat, which is designed for green roofs but it also appropriate for landscaping.
Our wildflower turf contains a mixture of wildflowers, herbs, and perennial flowers, but no grasses. It will bring a spectacular array of colours to a green roof that will attract bees and other vital pollinators from miles around. The spectacle it produces adds a stunning crown to the top of any building.
Wildflower turf is also low maintenance, which again makes it ideal for green roofs, needing to be cut just once or twice each year.
Our species rich turf is an 80/20 mix of wildflowers and grasses. The grasses make it slightly hardier than wildflower turf and laid on the ground, it can be walked on like a standard lawn if kept short.
Species rich turf can be cut short like a lawn but for a green roof, we recommend you let it grow longer to benefit from vast array of wildflowers it contains. Like wildflower turf, species rich is low maintenance and only needs to be cut once or twice each year.
Our Sedum Mat comprises of a mix of sedum plants to provide colour through the flowering period. It is lightweight, easy to install, low maintenance, and extreme drought tolerant.
How to lay a green roof
When laying a green roof, there are some extremely important aspects to consider. The first is weight. Unsurprisingly, growing substrate and plants add a significant amount of weight to a roof and it is imperative that the structure is capable of withstanding the extra weight placed upon it, not just in the short term, but for many years to come.
This is why, if you’ve considering adding a green roof to an existing building, you must consult an expert on the issue before going ahead. A residential surveyor or structural engineer will be able to tell you if the roof will take the additional weight without the prospect of damage or collapse.
Don’t forget, however, that its not just the weight of the green roof you will need to consider. A green roof needs to be maintained and that includes being cut. Therefore, the roof will need to be able to withstand the turf and growing medium, and at least one person with gardening equipment.
If it cannot, you might want to reconsider your plans for a green roof because leaving one to grow wild without maintenance will never look its best.
Green roofs typically have three layers; a drainage layer to allow water to run safely off the roof, a growing medium, generally between 75mm and 150mm thick, and the vegetation, in this case, the turf.
By layering the roof like this, the roots of the plants in the turf will grow through and bond to the growing medium, holding everything in place, and the drainage layer will ensure water doesn’t get trapped and increase the weight of the roof to dangerous levels.
Most green roofs we supply turf for are flat, but using this system, it is possible to install it on angles of up to 30 degrees. However, beyond this, gravity takes its toll and it is not possible to guarantee the roof won’t slip out of position.
If you’re laying a relatively small area on a flat surface, it is quite possible to do this yourself. However, for a larger, more complicated area that is sloped, it might be a good idea to at least get some help, or call in a professional.
Maintenance
Once the turf is in place, maintaining it is actually quite straightforward. The first thing you will need to do is make sure it is well watered. Doing this will ensure the flowers bloom through much of the year, creating a fantastic wildflower meadow effect on your roof.
Once the flowers die back, you will need to trim the roof. We would recommend a strimmer to do this as it is more portable than a mower, but however you choose to do it, you must wear the appropriate protective clothing and observe all relevant health and safety procedures. If in doubt, employ a professional to do it for you.
Before you trim, however, take a stick and go over the turf hitting the dying flower heads. This will ensure they release their seeds onto the turf for next year’s plants.
Strim, and then remove the cuttings so the seeds are able to germinate. Once this is done, continue to ensure it is well watered through any dry periods, and your green roof will be in great shape to blossom again later on in the year.
For more information on our wildflower turf, click here. To find out more about our species rich turf, click here. Information on our Sedum Mat can be found here.
ENDS