When you’re setting about a self-build, or renovating your property, there’s a lot to get excited about. You envisage your dream lounge with all the amenities you could possibly want to help you to enjoy your free time. 

You imagine a luxurious bedroom in which you can lay down your head after a hard day’s work. And equip it with everything that you need to drift blissfully to sleep. You might fantasise about your dream kitchen and all the good food (and lifelong memories) which can be made there. 

Or you may imagine how good it will feel to soak in your custom designed luxury bathroom at the end of a long day. Building your dream home involves an enormous investment of your time, effort, capital and faith. Not to mention enormous logistical undertaking so you should get excited about it. 

Your excitement is what will help you to navigate the twists and turns and stalls and frustrations you will inevitably encounter. But why limit your excitement to the most popular and widely used rooms in the house? There’s a whole lot more to be excited about!

Your roof, for example, may not seem like the most exciting element of a self-build or major renovation. However, as we’ll discuss at length, there’s a lot to get excited about! New developments (and trends) in roofing technology allow you to build a new roof with environmental care and ecological efficiency built into its very fabric. 

It can help to make your home a model of sustainability while also driving down your energy bills from the very day you move in. What’s more, it looks incredible and distinctive, too. A green roof can give any exterior an added element of wow factor.

But let’s start at the very beginning...

What Is A Green Roof?

A green roof is essentially a miniature garden or expanse of plant life that sits atop your roof

The “green roof” is a somewhat ambiguous term. There are many energy efficient roofing solutions that could be considered green by virtue of their environmental friendliness and contribution to sustainability. 

Adding solar panels to your roof could technically make it “green”. While adding metal shingles to your roof can help to insulate your home in the winter while reflecting sunlight in the more clement months. This could also be considered a “green roof”. The kind of green roof we’ll be discussing here is much more specific.

We’re talking about a quite literal green roof!

A green roof is essentially a miniature garden or expanse of plant life that sits atop your roof. While they have risen to prominence in an era of increased eco-conscience and interest in sustainability but the core concept is nothing new. In fact, turf roofs have been incorporated into our architecture for centuries. 

Examples of sod and turf roofing go all the way back to before the birth of Christ. However, green roofs as we know them today have their roots in mid 20th century Germany. Where a combination of bitumen and sand were commonly used in roofing as a fire prevention measure.

Over time vegetation would begin to grow on these roofs leading to the popularisation of deliberate seeding of plants on roofing for decoration.

A green roof is known by many names including “roof garden”, “eco-roof”, “living roof” and “vegetated roof”. Whatever you call it, it is comprised of a layer of vegetation atop a layer of soil / growth medium on top of your roof. With several layers between the substrate and the roof decking to ensure efficient waterproofing and insulation. 

We’ll go into more specifics shortly, but first, let’s look at why you may want to install a green roof...

A diagram of a green roof constructionA diagram of a green roof construction

Green roofing is made up a multiple layers

Advantages Of A Green Roof

With careful planning a veteran DIYer can install a green roof onto their property and enjoy years of the above benefits

At the risk of seeming flippant, one of the most obvious benefits of a green roof is that they look awesome. They’re distinctive and because our eyes are naturally drawn to vestiges of nature like soil, grass and plants they give us a little “feel good” boost whether we’re aware of it or not. 

What’s more, the sheer diversity of what can be planted on a green roof offers you enormous opportunities for customisation. Most roofs are, let’s face it, pretty unremarkable, but a green roof makes a powerful statement. It’s also a great way to show your commitment to sustainability and environmental protection on your sleeve.

But aesthetic beauty and epic bragging rights are just the tip of the iceberg in terms of potential benefits;

  • Heat absorption- Your green roof naturally absorbs heat energy from the sun to keep your home cool in winter without the need for power sapping temperature control.

  • Water absorption- The soil in your green roof also absorbs up to 70% of ambient rainwater. This is particularly useful in areas that receive heavy rainfall and are prone to flooding as your home can help to mitigate stormwater runoff. 

  • CO2 absorption- We all know that plants breathe in CO2 and breathe out oxygen so a green roof can improve air quality around your home.

  • Increase local biodiversity- Green roofs add much needed biodiversity to conurbations, helping to redress the balance between the manmade world and the natural world. 

  • Increase the lifespan of the roof- A green roof takes the brunt of the natural wear to which normal roofing materials are exposed. This can add much more longevity to your roof. 

  • Supports local wildlife- A garden roof can provide sanctuary to birds and animals living in the vicinity that again helps tpo redress the balance of nature. In an age of widespread habitat loss, it helps to know that you’re doing what you can to help local critters in need. 

  • Environmental stewardship- The appearance of a green roof doesn’t just promise bragging rights. It sets an example for environmental stewardship that your neighbours may well be tempted to follow.

Hopefully, by now you’re considering the benefits of adding a green roof to your self-build or renovation. But is this something that can be done without the expert help of a professional builder?

Yes. Absolutely!

With careful planning, a veteran DIYer can install a green roof onto their property and enjoy years of the above benefits. Needless to say, the better you know the anatomy of a green roof the more likely it is that your installation will go without a hitch.

Let’s take a look...

Anatomy Of A Green Roof

Your substrate should be light and fairly low in nutrient content comprised of a combination of organic and inorganic materials

A green roof may look simple and natural at first glance (that’s the beauty of it, after all). But there are numerous layers that are necessary to make a green roof logistically viable. Let’s start at the bottom and work our way up;

  • Roof decking- A green roof cannot simply be installed over existing roofing tiles. A structural engineering analysis should tell you the best materials to use for roof decking beneath your green roof.

  • Insulation layer (optional)- You may also want to install an extra layer of insulation for added energy efficiency. 

  • Waterproof membrane- Because green roofs absorb a lot of moisture, it’s imperative that you mitigate the risk of this seeping in through the roof deck and into your home. You’ll need to lay down an impervious waterproof membrane.

    Some membranes are rolled out over the roof while others come in a liquid form and are applied with brushes. An ethylene propylene diene monomer, similar to the underlining of a garden pond, is a popular choice. Your membrane should be able to cover all the roof imperfections and help you to build upon an evenly distributed layer.

    What’s more, when laid on thick enough your membrane should also be self-healing in the extremely unlikely event of a puncture. Your waterproof membrane should be fixed into place with a strong mastic seal. 

  • Root barrier- Depending on the type of membrane you use. You may or may not also need to incorporate a root barrier to prevent roots from burrowing into the structure of your roof and undermining its integrity.

    A high density polyethylene (HDPE) sheeting is advisable here. The seams and edges can be sealed with electric heat welding equipment to create an impervious and long lasting seal.

  • Drainage layer- While you want your green roof to absorb some ambient moisture. The right drainage is also important to ensure adequate drainage for obvious reasons. Your drainage layer will help you to strike the necessary balance. It will prevent your plants from drying out in warm months while also preventing flooding in Britain’s ample rainy days.

    A plastic eggshell drainage layer is a common choice, although you may understandably want to use something more natural and sustainable. Some people use a layer of gravel or pebbles although you should be wary as these can add exponentially to the weight of your roof. Some people use lighter natural materials like cockle shells as a lighter alternative to gravel.

    As well as your drainage layer. Your roof should also contain regular drainage outlets cut into the containment frame which facilitate the flow of water into your roof’s guttering. A layer of pebbles should also be used around the roof edge to prevent your drains from getting clogged. 

  • Filter membrane- Above your drainage layer should sit a filter membrane. This will act as a cup containing all the subsequent layers. It will allow water to seep through into your drainage layer while also filtering out soil particles. 

  • Substrate- Your substrate will contain the growing medium to nourish your plants, and which kinds of plants you grow will depend on your substrate’s depth. Avoid using garden soil as this can not only get extremely heavy and tightly packed when wet it can also have a high organic content. Facilitating the growth of unwanted plants and weeds which can complicate the growing process.

    Your substrate should be light and fairly low in nutrient content comprised of a combination of organic and inorganic materials. 70% inorganic and 30% organic is a good ratio to stick to. If you’re going for an ultra-sustainable green roof a combination of crushed repurposed house bricks and kitchen compost waste can make for an effective and sustainable growing medium.  

  • Growing layer- Finally, we get to the visible growth layer. What you grow will depend on the depth of your substrate although a sedum roof is a popular choice that can work well in virtually any substrate. 

A flat roof with a eco green roof sectionA flat roof with a eco green roof sectionA flat roof with a eco green roof sectionA flat roof with a eco green roof section

Your ECO green roof does not have to cover the whole roof area

Will A Green Roof Work On My Property?

To mitigate the risk of slippage, we recommend installing a chequerboard style wooden or metal grid

In theory, a green roof can be installed on any flat, or nearly flat, a roof that’s pitched at under 30 degrees. However, that’s not to say that you don’t need to apply careful planning to your green roof. 

In some cases, a lack of planning can lead to structural failure and collapsing because the roofing infrastructure was unable to bear the load. This is why you should always get in touch with a surveyor before attempting to install a green roof.

What’s more if you have a roof with a relatively steep slope (around 10-20 degrees). You’ll need to factor in how the additional gravitational pull will affect the plants you grow. To mitigate the risk of slippage, we recommend installing a chequerboard style wooden or metal grid laid atop your root barrier. 

The building’s load capacity should be adequate to take the weight of a garden to ensure stability. You’ll need to account not just for the dry weight of the roof’s components but account for the additional weight caused by absorption of the ambient water. 

The last thing you need is for your green roof to cave in the event of a heavy storm. A green roof needs to be able to support carry a dry weight of up to 65 lbs per square foot (psf) although this may vary depending on the thickness of your green roof.

A green roof on a flat roof with a chimneyA green roof on a flat roof with a chimneyA green roof on a flat roof with a chimneyA green roof on a flat roof with a chimney

On flat roofs, you can separate sections with gravel borders

Different Types Of Green Roof

You can live a more sustainable life by growing your own organic veggies, you can better support local wildlife

Not all green roofs are created equal. And the kind of green roof you install will depend largely on which thickness of substrate your roofing infrastructure will support. Generally speaking, however, the types of green roof you can install fall into three camps. 

  • Intensive- Roofs with a thick substrate (anywhere between 50mm and over 200mm).

  • Semi- Extensive- Roofs with a fairly thick substrate (100-200mm) but a potentially larger surface area.

  • Extensive- A much shallower substrate, typically between 20mm and 100mm.

Let’s take a closer look at what can be grown on each;

  • Extensive roofs- Their light and shallow nature makes them suited to hardy and low maintenance mosses as well as stress tolerant grasses.

    Extensive roofs tend to require little maintenance by virtue of their shallow substrates. And the limited vegetation they can support so they will require much less weeding and inspection than the average garden. These are the kinds of green roofs that lend themselves best to retrofits. 

  • Semi- Extensive roofs- These have somewhat more depth than extensive roofs and are therefore permissive of a little more biodiversity in the plant life you cultivate on them.

    They are also fairly low maintenance and can be considered to offer the best of both worlds for roofs that have the infrastructure to accommodate them.

  • Intensive- The thicker substrate of an intensive roof means that it can grow a much more diverse range of plants including shrubs, grasses, flowers. And even herbs and vegetables if you have the patience and gardening knowhow.

    While extensive and semi-extensive roofs can usually be left to their own devices with very little maintenance. An intensive garden needs to be readily accessible for maintenance and cultivation. What’s more, their increased weight will mean that they need much more intensive roof support.

    However, if you have the time and attention to dedicate to an intensive garden, it can be very rewarding. You can live a more sustainable life by growing your own organic veggies, you can better support local wildlife. Heck, you can even enjoy a picnic or a game of football on an intensive roof. They’ll also offer you better insulation and water retention, too. 

A sedum green roof installed on a pitched roof with rooflightsA sedum green roof installed on a pitched roof with rooflightsA sedum green roof installed on a pitched roof with rooflightsA sedum green roof installed on a pitched roof with rooflights

ECO green roofs look stunning as the plants grow and bloom

Do I Have To Make The Whole Roof Green?

Not at all. The beauty of a green roof is that there’s enormous scope in which to make it your own. So long as you’ve made sure that your roof can support the weight of your intended green roof, you can let your imagination run wild. 

You can make as much or as little of your roof green as you like. You can neatly bisect your roof. Turning half of it green or arrange the green sections into shapes and patterns with pathways between composed of your normal roof decking.

What’s more, if you like the idea of a green roof that cascades over the side of your building and down a side wall. You can apply the same principles to create a green living wall for a seamless effect that can provide sanctuary for a greater array of wildlife. 

Sedum is a great choice for a green wall although coral bells (Heuchera), sedges and fragrant thyme are also wonderful choices. They’re light and require only a very shallow substrate.

This seems like a great place to segue into discussing which plants lend themselves best to grow on a green roof...

What Can I Plant On A Green Roof?

Provided that it’s properly planted, sedum can be left alone with virtually no maintenance

When the infrastructure for growth has been established, it’s time to get to the fun part… Planting. However, nobody wants their green roof to quickly become a dead, brown roof. What you can grow will largely depend on the type of green roof you have installed as well as the time and effort you can spare to maintain it. 

The wonderful biodiversity afforded by a green roof is that it can be as low maintenance or intensive (pun intended) as you want it to be. Let’s take a look at some of the plants you can grow on your green roof and which types of roof they’re best suited to…

  • Pre-vegetated mats- A pre-vegetated mat or blanket is a popular way to get green roofs up and running without the need to plant individual seeds or cuttings and wait for them to grow. These usually consist of sedum or wildflowers or a combination of both.

    They are rolled out onto your substrate in much the same way as turf. This is a great option for extensive roofs and those who want to get up and running as quickly as possible. 

  • Sedum- We’ve already talked briefly about the benefits of a sedum roof. Sedum is a hardy Alpine plant that’s used to growing in harsh and elevated conditions. Because it’s used to growing on mountains it will have no problems growing even in shallow extensive substrates.

    What’s more, sedum is one of the lightest, most inexpensive, easy to plant and extremely low maintenance plants around. This makes it the perfect choice for the DIY green roof (especially when budget and logistics are key factors).

    Provided that it’s properly planted, sedum can be left alone with virtually no maintenance needs. Outside of the odd visual check and a little very light weeding every once in a while.

    Another great thing about sedum is that it has so many different variants, all of which have subtly different idiosyncrasies of appearance. And a colour from gold sedum (an absolute gift for local honeybees) to pink and cheerful widow’s cross and fluffy white stonecrop. 

  • Wildfowers- Even extensive garden roofs may be able to grow a range of stunning wildflowers. Including beautiful golden birdsfoot trefoil, vipers bugloss, sempervivums (house leaks), sweet smelling and multicoloured yarrow and pretty pink seathrift.

    For a shock of vivid blue, you may also want to consider muscari or grape hyacinth which grows on the mountains of Turkey. And as such is at home even in shallow green roofs.

  • Trees and shrubs- Depending on the depth of your substrate you may be able to plant a range of beautiful shrubs and small trees. Owners of semi-extensive and intensive green roofs may find that they have a surprising amount of latitude in terms of what small trees and shrubs they can grow.

    Look for trees and shrubs which grow to a maximum of around 3 feet. For example, a dwarf cypress lends itself well to a green roof.

  • Herbs- Thyme is a hardy herb that is not only great for cooking. It can also grow in extremely shallow soil making it suitable for all kinds of green roofs. Oregano is similarly ubiquitous and low maintenance.

    Lavender can grow well in roof gardens but is better suited to intensive or semi-extensive roofs. Chives, being a bulbous plant, will fare well in extensive green roofs. Local favourites like basil and marjoram will also flourish on your roof.

  • Vegetables- Some intensive green roofs may lend themselves to the growing of veggies. Intensive substrates around 200-300mm deep can actually support a host of favourite veggies.

    Lettuce, spinach, radishes and Swiss chard will grow in substrates of this depth. If you can afford to go a couple of inches deeper you can even grow broccoli, carrots and cauliflowers. 

Don’t forget that even if you can’t plant something directly into your green roof. You may still be able to grow it in a pot as part of a thriving rooftop garden. By rule of thumb, you should aim for biodiversity in your green roof whatever you choose to grow as monocultures typically struggle to create a self-maintaining community of plants. 

You should also consider which plants will need the most water and plant accordingly, especially if your roof has a slope. Put drought-resistant plants nearest to the top as they will get the least water access.

The beauty of a green roof is that you can plant in accordance with your property and your preferred ecological benefits. You can grow plants which will better cater to local wildlife or grow plants which can make your daily dinner plate more sustainable. 

So long as you ensure that your substrate will support what you want to grow. And that your roof is strong enough to support it, your only limit is your imagination!

two tradesmen applying a coloured wall render to a new houseA close up of sedum plants on an eco roofA close up of sedum plants on an eco roofA close up of sedum plants on an eco roof

The covering of small plants is great for the environment

How Much Will A Green Roof Cost?

As you might expect, the cost of a green roof will depend on its depth and weight. As well as the specifics of your property. Broadly speaking you can expect a shallow extensive roof to cost you around £50 per square metre. 

A fully planted intensive roof will likely cost you much more- in excess of £200 per square meter. As you may expect, a semi-extensive roof will likely fall somewhere in between. Intensive green roofs will also require much greater structural reinforcement which may further affect the cost. 

For this reason, many first-timers choose to install extensive and semi-extensive green roofs as they are lower in cost and lower maintenance without the need for regular access.

How Do I Maintain A Green Roof?

Remove any unwelcome weeds in your green roof proper by gently twisting and lifting them out by the root

Maintaining a green roof, especially an extensive green roof can actually be extremely straightforward. The combination of shallow substrate and carefully chosen low nutrition growth media will preclude the growing of most plants other than the ones you’re actively trying to grow. 

As such, you can expect your weeding duties to be fairly minimal for an extensive and even semi-extensive roof garden. While you won’t need to access your green roof daily, it’s highly beneficial to be able to access your roof occasionally. Once or twice a year, it’s a good idea to carry out the following checks;

  • Check that your drainage outlets are clear and free from unwanted vegetation (that’s where those pebbles come in). 

  • Make sure plants are well watered in long spells of dry weather, especially those that are recently planted (12 months or less).

  • Make sure that the gravel or pebbles around the edging are also free of weeds and unwanted vegetation.

  • Check for bare spots on your green roof. Re-plant them with cuttings, bulbs or seeds as appropriate, ensuring that the area will get sufficient water to sustain the plant in question.

  • Remove any unwelcome weeds in your green roof proper by gently twisting and lifting them out by the root. Whatever you do, avoid pulling them out with a fork as this can risk damaging the waterproof membrane.

Of course, depending on what you plant in an intensive roof, you may need to carry out further maintenance to ensure that you create the optimum growing conditions for your plants, although the same basic checks should still be carried out. 

Do I Need Planning Permission For A Green Roof?

Strictly speaking, no. Green roofs don’t usually require planning permission and believe it or not there are no universally accepted standards for a green roof in the UK (although German FLL guidelines are widely considered the gold standard and are followed internationally). 

That said, it is considered good form to at least notify your local council and double check that you don’t require planning permission. It’s worth remembering that while planning permission may not be needed, a green roof needs to conform to UK building codes which is why it’s so important to get a surveyor involved in the planning stage.

Close up of green roofing on a slope roof with gutteringClose up of green roofing on a slope roof with gutteringClose up of green roofing on a slope roof with gutteringClose up of green roofing on a slope roof with guttering

Green roofing systems are highly energy efficient

Are There Any Caveats That Come With Installing A Green Roof?

We’ve looked quite intensively at the pros of a green roof, but are there any cons? There are certainly a couple of things which should be considered before you commit to this undertaking. 

  • Risk- A green roof brings with it some inherent risks, which is why careful planning is so essential. The risk of a collapse can be a consequence of improper planning and poor maintenance can also invite the possibility of leaks.

    If unwelcome self-seeding plants develop a string root structure they risk permeating the roof and creating leaks. And the complexity of the average green roof can make it hard to determine the leak’s source and act upon it. 

  • Limitation- For most who grow green roofs a limited stock of plants like sedum and wildflowers is enough. But those who want more diversity than their roofing infrastructure will allow may become frustrated.

  • Maintenance- Some who install intensive green roofing may find that it requires more maintenance than they first realised. The trouble of course is that you can’t exactly take it down.

    Once you’ve committed to it, you must also commit to the maintenance or risk the damage that can be done by unwelcome self-seeding visitors.

In Conclusion

A green roof can make a wonderful addition to your self built or renovated home. But your enjoyment and benefits will depend very much upon careful planning and painstaking implementation.