Green roofs have been around for millenia. Arguably the most famous of all were the Hanging Gardens of Babylon – considered one of the Seven Wonders of the Ancient World – constructed in 6th century BC.
Now whilst more modern construction has developed significantly, the core principles remain the same. Green roofs:
- Increase the lifespan of your roof by improving it’s structural integrity
- Reduce pollution
- Increase biodiversity
- Improve drainage
Alongside a frankly mind-boggling array of additional living roof benefits.
Now obviously the Babylonians weren’t looking to reduce pollution or increase biodiversity, so we aren’t completely aligned. But times have changed – now this all comes at a cost.
And as sustainability goes, they aren’t a cheap, money-making opportunity. If your primary goal is to earn money, the initial outlay may be enough to put you off. And that’s without factoring in the ongoing maintenance.
But in reality green roofs are an excellent long-term investment. There are multiple case studies that prove their financial efficacy (which we will come onto later), but you need to be prepared to either spend a considerable sum on a professional project and plan for future maintenance.
Green Roof Grants in the UK
Currently there are no direct UK government grants to assist with the initial cost of installing a green roof.
Recently the government has launched the green homes grant – one which we had hoped would include green roofs. As a homeowner you can apply for a voucher towards installing energy-efficient improvements to your home. This could include:
- Insulating your home to reduce energy use
- Installing low carbon heating
As green roofs unequivocally insulate your home and reduce energy usage, we expected this grant to include green roofs. As of now it’s unclear, but as the government will contribute two-thirds of the project (up to £5,000) we have high hopes that green roofs will be eligible.
Average Cost of a Green Roof in 2022
Clearly the cost of a green roof varies enormously. A large scale, commercial green roof on an expensive high-rise apartment block in London will cost 100s of thousands of pounds.
A DIY project on your garage can cost as little as £500. The huge disparity between potential green roof project prices is considerable, as there are an incredible number of variables that will alter the price of your green roof.
But ultimately we all want a rough idea of how much our project is going to cost don’t we?
Cost per Type of Green Roof (m²)
Cost per m²
£100 – 200+
£100 – 140
£60 – 100
Soil Layer (mm)
100 – 200+
100 – 200
20 – 100
Low – Medium
Medium – High
Medium – High
Low – Medium
Green Roof Installation Cost
There are multiple things to consider when discussing living roof installation:
- Design: If you aren’t undertaking a DIY project, you will absolutely need architectural and aesthetic expertise
- Materials: Extensive green roofs use cheaper materials than intensive green roofs. And less of them. So the type of roof makes a difference material wise.
- Accessibility: Green roofs need to be installed on roofs pitched at no more than 30°. The more complex the construction and project accessibility, the more expensive it will become.
- Type of roof: In this case we’re talking about modular vs rollout green roofs.
Modular roofs fit together like a giant jigsaw, where all the pieces fit seamlessly together. They can form a seamless green roof with great drainage. This form of green roof works best in hard-to-reach places and is more expensive.
Rollout roofs are lightweight and cheaper than modular to initially install, but it’s harder to carry out long-term maintenance. i.e. You’d have to remove the roof to access the roof underneath. This is a cheaper, more lightweight form of roof with lower, but more complicated, maintenance costs.
Cost of Green Roof vs Conventional Roof
The good news for us green roofers is that – in the long-run – a green roof will save you money. Unless your DIY project goes horribly wrong!
Even though a 100m2 intensive roof could cost well in excess of £20,000. And if you’re considering a green roof, you almost certainly already have a roof – Otherwise I suggest taking a step back and a deep breath – so a true comparison is very difficult to make.
Roofs are a premium home product. And the green variety should extend the lifetime of your roof by 200 – 300%. By increasing the structural integrity of the roof and protecting the membrane from corrosive UV rays (and extreme temperature fluctuations), studies have revealed that the lifetime of roofing membrane can by lengthened by 40 – 50 years.
So whilst green roof installation is expensive, so is the cost of replacing a roof. And we like to think of a green roof as an eco-friendly roof replacement. One that increases your roof’s longevity and reduces your energy bills.
And in the UK more energy is spent artificially cooling buildings in the summer than heating them in the winter. Completely counter-intuitively – to us at any rate. 10% of the UK’s total energy expenditure was spent on cooling buildings – primarily offices – in 2017.
So installing something that improves a building’s temperature regulation is an seasonal energy-efficient winner. For you and your city.
Then we need to consider maintenance. And herein lies a significant difference in both care and cost.
Green Roof Maintenance Cost
Even though green roofs are a low maintenance medium, they still need continued care and attention.
An intensive green roof requires year round maintenance because of the diverse planting regime, longer membrane life and improved insulation properties. Whereas an extensive living roof may only need a couple of minor checks a year due to the use of low-growing, stress-tolerant grasses, mosses and sedum.
Extensive roofs are the much cheaper, lower maintenance option. Their shallow, lighter growing medium makes getting to the roof itself much simpler and the lighter weight doesn’t have the same potential to warrant structural inspection as frequently.
And the low-growing, stress tolerant grasses and succulents associated with extensive roofs are much hardier than their intensive counterparts. Checkout our overview of the best plants for a green roof to see why plants make such a huge difference to maintenance.
However you will need to check the drainage system is clear from debris a couple of times a year to prevent serious leakage issues. Not something any of us want.
Intensive roofs consist of a much thicker soil layer with a variety of grasses, herbs, flowers and shrubs. Intensive roofs must be more accessible for maintenance purposes. Whilst they offer better structural support, water absorption and habitation for wildlife – the maintenance required can be significantly more expensive. You’ll also need to keep drainage outlets free-from unwanted plants and debris.
Maintenance Cost Variables
- Plant and material care: this could include feed, professional green-fingered tradesmen, de-weeding, irrigation testing and watering on a relatively consistent basis – weather dependent of course.
- Capital cost: Some less accessible roofs in particular will require machinery hire and thicker, intensive roofs will need professional equipment to deal with the membrane layer and roof itself.
- Professional evaluation(s): For larger, more intensive roofs you’ll need professional assistance to ascertain the need for maintenance.
- Weather: During very wet seasons green roofs can have problems retaining nutrients – and replanting a green roof can be an expensive operation.
Living Roof Disposal Cost
An oft overlooked, but potentially important cost to consider when purchasing a green roof.
Oft overlooked because the overwhelming majority of people who purchase a green roof don’t have to concern themselves with it’s disposal, as you may be disposed yourself. But if your home has been in the family for generations – or you’ve inherited a home with a green roof – then you may want to consider the disposal costs.
At the end of a green roof’s lifecycle materials can be landfilled, reused or recycled – but many cities don’t have the necessary facilities for recycling. Hence why the maturity of the market matters.
And these landfill costs depend on multiple factors, such as:
- Available technology
- Location (i.e. how far you have to transport the goods)
- Size of the facility
- Available landfill capacity
One European report from 2012 claims that the disposal cost for an entire green roof is estimated at $1,120 / ton. Of course this isn’t a perfect estimate (not just because it’s in dollars) as European green roof markets are at varying stages of maturity. But it provides an expensive representation.
Now you know (roughly) how much green roofs cost over their entire lifecycle. You can make a decision about whether it’s right for you – do you think the individual energy saving and aesthetic benefits are worth the additional cost?
Maybe the wider biodiversity and environmental benefits swing it for you. Either way next up you need to get a quote from a few green roofing companies to find out which one is right for you. And that’s where we can help!