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What I wish I knew before I put a green roof on my house

21 May 2024

Dr Anastasia Mylona, technical director at CIBSE, shares her experience trying out nature-based solutions in her own home.

What I wish I knew before I put a green roof on my house
The green roof only needs to be accessed for watering and maintenance. Image credit: Dr Anastasia Mylona

Nature-based solutions (NBS) and their use in the built environment have fascinated me since the moment I trained to become an architect.

So when we decided to renovate our house, it was clear to me that we needed to look at opportunities to integrate NBS where possible.

The new extension in the back of the house seemed like the perfect opportunity to install a green roof.

Benefits of nature-based solutions

There’s irrefutable evidence of the positive impact nature has on humans. Benefits include:

Nature-based solutions are also key in adapting to and mitigating the effects of climate change.

They help to improve flood management and water quality, decrease riverbank erosion, gain biodiversity and sequester (trap) carbon from the air.

And yet such solutions aren’t as widely used as one would expect considering their clear benefits to the environment and society.

Learn more

Picking the right green roof

I researched all my green roof options, looking at the structural, installation and maintenance requirements and how easily they’d integrate to the rest of the house.

There are two main types.

Intensive roofs

These require a reasonable depth of soil to grow large plants or conventional lawns.

They’re considered intensive because they require more labour, like irrigation, feeding, and other maintenance.

Intensive roofs could be used as parks, with easy access for the users and for maintenance purposes.

They are also the costliest to install and maintain.

Extensive roofs

Extensive roofs are the most self-sufficient and need little maintenance.

They are also the lighter option, as they’re set on very thin soil, and in most cases, don’t require structural reinforcement.

They’re only accessed for maintenance and are cheaper to install and maintain.

We decided to go with an extensive roof and plant sedums, which are succulents with leaves and star-shaped flowers.

Because of the system’s lightweight nature, it didn’t need extra structural support and the only maintenance needed was to apply a slow-release fertiliser once a year.

We also just needed to water when there’s an extensive period of no rain (more than a week).

The fear of the unknown got in the way

The push back we got was surprising.

So much so that we questioned our decision and temporarily decided to go with a traditional felt roof.

Our builders’ main concerns were integrating the green roof with the existing sloped structure, weather proofing to avoid water leaks, extra costs, and the risk of the unknown.

While installing the felt on the roof I realised that our original decision was the right one.

Despite potential delays and extra costs, I was determined to address the concerns and continue with the installation of the green roof.

Installation of the green roof. Image credit: Dr Anastasia Mylona
Installation of the green roof. Image credit: Dr Anastasia Mylona

Sticking to our choice – but still facing challenges

The roof needs to be put in by an approved installer and be signed off by an independent assessor. A 20-year guarantee certificate is then provided when it’s finished.

The green roof project manager agreed to be present and direct the builders when they were connecting it to the sloped roof to make sure it was weatherproof.

Once the roof was installed, we had to justify our choice to our local authority’s building control, who required detailed documentation. There were a lot of questions.

The main concerns were weather proofing and ensuring that the wooden joists below the roof didn’t rot or sweat (creation of condensation patches on the ceiling).

And then we had to deal with the neighbours.

From questions such as ‘why did you put a garden on your roof?’ to visits from the local council because our neighbours had reported privacy concerns – they were worried that we would sit on the roof and look into their garden.

I had to repeatedly explain the benefits of the green roof, justify our decision, and reassure the neighbours that it’s not a garden we use daily, but only access for maintenance.

Our neighbours are still taking videos every time we get on the roof for maintenance.

The green roof today

Yes, the green roof and its installation costed significantly more than a simple felt roof.

It required scaffolding, careful supervision and monitoring of the installation and integration process, and a lot of paperwork.

But since it’s installation two years ago, there have been no problems.

No water leakages and minimum maintenance. It absorbs rainwater and releases it slowly into the drainage.

The green roof in autumn. Image credit: Dr Anastasia Mylona
The green roof in autumn. Image credit: Dr Anastasia Mylona

It’s resilient to all weather and provides enhanced thermal conditions in the extension below.

The room underneath the green roof is the warmest in the winter and the coolest in the summer by a few degrees so we tend to mostly spend our days there.

Birds come every day and bees visit the flowers in the spring.

It changes colours through the seasons and provides beautiful views from the windows, giving us pleasure every day.

What I learned from the experience

Going through this experience helped me see that although the systems and practices are well developed and their performance guaranteed, there’s still a long way to make them mainstream.

Traditional builders, building control and ultimately, the public, aren’t familiar with nature-based solutions. I found that their first response was to dismiss them.

If I didn’t know more about them, I probably would’ve been discouraged from installing the green roof in my house.

It’s important to embed nature-based solutions and their benefits at all levels of professional training and education.

But we must also inform clients, policymakers, and the public.

Increasing the public’s understanding of the benefits of green spaces and biodiversity is the key to the systemic uptake of NBS.

Changing the narrative from ‘nature for nature’s sake’ to ‘nature for people’ is fundamental in changing established perceptions.

  • Dr Anastasia Mylona, technical director at the Chartered Institution of Building Services Engineers (CIBSE)