A Complete Guide to Green Roofing

Sustainable structures and aesthetics are incredibly popular right now, with the trend for green roofing flourishing in the UK, much like the foliage that the roofs themselves support. Indeed, the market for green roof installation is currently experiencing a 17% increase year on year, thanks to the many benefits that green roofing boasts over traditional roofing options.

As one of the UK’s leading green roof installers, Southern Cross Projects Roofing & Waterproofing has put together this complete guide to green roofing to answer any questions you may have on the topic, whether it’s deciding which type of green roof is right for you, learning more about the green roof installation process or delving deeper into our list of green roof benefits.

Contents

• What is a green roof?
• Different types of green roofing
• Green roof benefits
• The green roof installation process
• Green roofing FAQs
• Green roof installation by Southern Cross Projects

What is a green roof?

Also known as “living roofs”, “grass roofs” and “roof gardens”, green roofs are covered – either partially or in full – with thriving plant life and vegetation. The type of greenery used can range from simple sedums  and sempervivums, to ornamental grasses, flowers, shrubs and trees. However, your chosen verdure is not just a matter of personal preference – the fauna you opt for should be appropriate for your roof size and structure, as well as aligning with local climate conditions and your preferred aesthetic.

Designed to be self-sustaining, green roofs work well on all kinds of residential and commercial properties, regardless of whether they have a flat or sloped roof profile. The important thing is to ensure that you have the correct layering. The exact structure of your green roof will depend on the type of living roof you opt for but, generally speaking, your green roof will consist of:

1. A bottom layer, typically made from concrete or flat board (screed);
2. A waterproofing barrier layer;
3. A root-proof layer to protect against root damage to the underlying structures;
4. A green roof drainage system appropriate for your greenery (which may or may not include a fabric filter layer to protect your soil);
5. And finally, a soil or growth substrate layer, followed by your plants.

As you can see, successful green roofs require careful planning, forethought and experience – whether you’re looking for a living roof that blends seamlessly with the surrounding natural landscape or want to ensure your property stands out as an emerald oasis in its urban setting.

Different types of green roofing

As mentioned above, green roofing techniques can be applied to all kinds of existing roof structures. Whilst the low incline of flat and shallow-pitched roofs makes them ideal for roof gardens, facilitating quick and easy installation of effective drainage systems, it’s still possible to fit green roof systems to sloped and steeply pitched roof frames, as well. In fact, sloped green roofs work particularly well with solar panels, since the additional greenery can help to make photovoltaic devices more efficient.   

Homeowners and businesses alike choose to fit green roofs for a variety of reasons, with the intended purpose ultimately determining the green roof type, as well. For example, whilst biodiverse green roofs are designed with the aim of supporting local ecosystems, detention green roofs are designed to temporarily detain rainwater, helping to prevent flooding of the surrounding area. It’s all a matter of careful planning and design.

With this in mind, there are three main types of green roof systems to choose from, each of which are described below. Remember, it’s important to ensure that your chosen solution meets your unique roof-size, budget and maintenance requirements.

Intensive green roofs

Intensive green roofs are one of the most impressive types of living roof to be created, as their structure allows for a greater variety of plants and trees. Designed to replicate the natural environments we might find on the ground, they require intense landscaping to achieve. As such, they tend to work best on larger properties, particularly as they require a deeper, heavier layer of soil to support a thicker layer of vegetation. Whilst intensive roof gardens are incredibly eye-catching, helping your building to stand-out against others, they do require a higher level of maintenance than other types of green roofs.

Extensive green roofs

Extensive green roofs are the most popular type of living roof amongst homeowners, thanks to their low-maintenance, lightweight structure. Indeed, they have a shallower layer of soil or growth medium than intensive living roofs, meaning they require little to no upkeep. In fact, the self-sustaining greenery they support grows almost instantaneously, standing at an average height of just 80-100 mm. Examples of extensive green roof plants include grasses, moss, sedum and small flowers.

Semi-Extensive green roofs

The growth medium layer on a semi-intensive green roof (also referred to as a semi-extensive green roof) is deeper than the soil on an extensive green roof but shallower than the soil on an intensive green roof. As such, they fall somewhere in the middle when it comes to maintenance and the types of vegetation they can support. This type of green roof is great for making buildings unique and interesting without worrying too much about maintenance. Smaller plants tend to work well but semi-intensive living roofs cannot support larger shrubs or trees.

Green Roof Benefits

Green roofing looks incredible. Nevertheless, the benefits of green roofs extend far beyond aesthetics. These natural wonders also help to support the environment, reduce your energy bills and even boost your business’s branding potential. At Southern Cross Projects Roofing & Waterproofing, we’re proud to offer such a positive and versatile service, bringing a range of green roof benefits to both commercial and residential clients alike.

Learn more about the myriad of green roof benefits below.

1.      Aesthetics

When it comes to green roof benefits, the first thing that springs to mind is aesthetics. Green roofs look appealing and can help to attract potential customers to business properties. Meanwhile, installing a green roof on your residential property helps to improve the overall look of your neighbourhood.

2.      The environment

Supporting local wildlife and helping endangered species like bees to thrive is one of the most rewarding green roof benefits. Biodiverse green roofs are particularly great when it comes to creating an ideal habitat, as they are specifically designed with nature in mind.

3.      Community

Passers-by are sure to appreciate the colour and charm your new green roof injects into the area. But, in addition to promoting visual wellbeing, your new green roof also helps to filter the air, making things more pleasant for your community. Detention green roofs can even prevent local flooding by detaining heavy rainfall.

4.      Your property

The extra layers of greenery and growth medium on top of your roof protect it from common wear factors like the sun and rainfall, meaning your roof will last longer. Another benefit of green roofs is that they add value to your property or home.

5.      Cost savings

Green roofing consists of many different layers. As such, it naturally insulates your property, helping to keep your home or business warm in winter and cool in summer. This will ultimately reduce your energy bills, meaning you will pay less as you also reduce your carbon footprint.

Green Roof Installation Process

Now you’re familiar with the many benefits that green roofs can provide, you may be ready to start planning your own living roof installation. We would always recommend finding a qualified local green roof installer to support you throughout this process, to help you determine the most appropriate structure and types of plants for your green roof.

Contractors need to consider the slope of your roof before they can begin planning. If your roof or structure sits at an angle of 10º or below, it will be classed as a flat roof; anything above this will be classed as pitched. Whilst green roofs can be installed on either, the angle will generally determine the type of green roof that can be installed. For instance, extensive and semi-extensive green roofing tend to work best with flat roofs, which are suited to shallower soil beds, whilst pitched roofs are able to support intensive green roofing with a thicker layer of growth medium, as well. With careful planning, anything is possible – it’s simply a matter of taking the essentials into account.

As one of the UK’s leading green roof installers, Southern Cross Projects Roofing & Waterproofing takes great pride in ensuring that the appropriate planning and expertise goes into creating your new green roof. Our experienced engineers perform a detailed survey of your property to determine the most appropriate type of green roof for you, before our skilled craftsmen get to work designing a unique system specific to your property and requirements. They will verify capacity and irrigation before obtaining any relevant planning permission from your local council.

Following this, they begin implementing the six simple steps below to complete your green roof installation.

Step 1: Waterproofing your roof deck

The first step in constructing a green roof is waterproofing the roof deck. As leading waterproofing experts, Southern Cross Projects ensures this is done to the highest possible standard, using our innovative liquid polyurethane formula to create an unrivalled impermeable membrane that will protect against leaks and any moisture that might accumulate on top of your deck. Our waterproof roof barrier also prevents water from seeping into any cracks in the deck itself.

Step 2: Adding a root barrier

Next, the root barrier is installed over the waterproof membrane. This layer is designed to keep tree roots away from your deck and protect the structural integrity of your roof. This stage is important as root growth could result in damage to your waterproofing layer, and consequently, in water leaking into your building.

Step 3: Installing a drainage membrane

A drainage membrane is then installed on top of the root barrier to allow water to drain off your green roof effectively. This helps to prevent the build-up of excess moisture and ensures that your roof will retain its emerald landscape for years to come.

Step 4: Fitting a filter layer

This step involves fitting a filter layer between the drainage membrane and the green-roof substrate. This geotextile filter prevents any soil particles from entering into the drainage layer and causing blockages and other issues. When your green roof is installed by a certified green roof installer like Southern Cross Projects Roofing & Waterproofing, unrivalled quality is assured at every turn.

Step 5: Adding your green-roof substrate

Your green-roof substrate or growth medium forms the base of your green roof. It provides essential nutrients that your plants and greenery need to flourish. It’s essential that you choose a high-quality growth medium, as it has such significant impact on the success of your green roof in the long term.

Step 6: Planting your vegetation

Finally, the fun part – planting your greenery! Choosing the correct plant life for your green roof is essential. The range of plants available is incredibly vast, regardless of the type of green roof you opt for. However, certain plants work best with certain types of green roof, as explained briefly below.

• Intensive green roofs: Hardy plants that can tolerate drought, sun and wind work best. Examples include succulents, palms and small shrubs.
• Extensive green roofs: Moss or mat-forming species of sedum are good options. Depending on your location, ferns could also be used in dry, shady conditions.
• Semi–intensive green roofs: Also known as semi-extensive green roofs, dry-habitat perennials and ornamental grasses work best. Bulbs and small allium species are another great option, particularly when these wildflowers are native to the UK.

In addition to the above considerations, you might like to ensure that your chosen plant life is appropriate for the local climate and is capable of supporting nearby wildlife. If you would like more detailed advice, the Royal Horticultural Society has put together this handy guide on which plants are most suitable for each type of green roof.

Green roofing FAQs

How do green roofs help the environment?

Biodiverse green roofs are specifically designed to create useful habitats for local wildlife. As such, they’re a great way to protect endangered species like bees, whist encouraging further pollination of your local area.

Whilst biodiverse green roofs are likely to have the greatest effect, any additional greenery you bring to your town or city has a positive impact. Indeed, the environmental benefits of green roof installation extend far beyond local flora and fauna. For instance, planting greenery on your roof also reduces its overall temperature, which in turn, makes solar panels more energy efficient.

Finally, any additional plant life you introduce will help to collect rainwater. With less water running off your roof, the ground will become less saturated, reducing the likelihood of flooding in your local area. This is especially true of detention green roofs, which are specifically designed for this purpose.

How do green roofs save energy?

Adding an additional layer of flora to your roof ultimately provides improved insulation. As such, less heat will escape from your property through the roof in winter, lowering your energy costs as a result. Likewise, your green roof plants will help to keep your property cool in summer, meaning you will spend less money on air conditioning.

Another way in which green roofs help to save energy, however, is through careful combination with photovoltaic panels. Solar panels become much more effective when installed directly above greenery and vegetation, as they are less likely to overheat. The more green energy you can produce and store, the better – it’s a win-win.

Do green roofs require maintenance?

Thanks to their simple soil structure and the fact that they are covered in hardy, self-sustaining vegetation unlikely to grow in height, extensive green roofs are the easiest type of living roof to maintain. In fact, unless you notice any potential issues with your roof, like cracks or leaks, you are unlikely to have to take any action for your extensive green roof to continue to thrive.

Whilst intensive and semi-intensive (also known as semi-extensive) green roofs do require a little more maintenance owing to their more diverse plant life, they are still incredibly low maintenance and require little attention. There are just a few small steps you may need to take once or twice a year to ensure your green roof ecosystem remains optimal (the experts at Southern Cross Projects can do this for you):

1. Inspect your roof: We’ll check for any weeds that may have sneaked their way into your green roof ecosystem, ideally in the spring and autumn. We can also check your drains, gutters and drainage systems as we work for greater peace of mind.
2. Fertilise your greenery: We’ll feed your plants at the start of the spring and the autumn, where necessary, to ensure they have all the nutrients they need to truly thrive.
3. Potential irrigation: Watering isn’t usually necessary, unless you live in a particularly dry climate. However, it can help to keep certain sedum roofs looking their best.

How much does a green roof cost?

The cost of your green roof will ultimately depend on the size of your property and the type of living roof you opt for. Generally speaking, the larger your property, the more your green roof will cost. However, other factors like soil depth and the type of plants you choose also have an impact. As such, it’s always advisable to discuss your requirements with us in detail before requesting a no-obligation quote. That way, you’ll get a more accurate assessment of how much a green roof is likely to cost.

Green Roof Installation by Southern Cross Projects

As you can see, installing a green roof on your property provides an array of benefits for you, your property and the environment. At Southern Cross Projects Roofing & Waterproofing, we strive to create captivating green-roof ecosystems that protect your building from the outside elements, as they blend in with the natural world around you. Our environmentally friendly methods combine the elegance of nature with the functionality of top-quality roofing, guaranteed to be installed correctly, leaving your home or business premises blooming beneath a sustainable emerald canopy.

Contact us today to learn more about how we can make your green roof vision a reality.