Do Green Roofs Provide Insulation?
Yes green roofs provide insulation – both for heat and sound – which makes them a sustainable solution for cities to mitigate the effect(s) of urbanisation. Their ability to retain heat in the winter and mitigate heat gain in the summer provide essential cross-seasonal benefits when it comes to energy consumption.
The deterioration in climatic conditions and the impact the urban heat island effect has on global warming makes green roofs an effective tool in the fight against climate change. Such is the energy demands created by buildings – particularly in urban areas – looking for ways to make them more efficient and cost-effective is essential.
How does a Green Roof Insulate?
Green roofs have a regulatory effect when it comes to heating (and cooling) cycles. The soil and plants act as a thermal mass on top of the roof, retaining heat (and sound) far more effectively than a traditional grey roof.
And, as stands to reason, the type of green roof has an effect on the roof’s insulation capacity. Thicker, denser intensive roofs retain heat far more effectively than their lightweight, extensive counterparts.
And they are really effective. Particularly in warm weather. In this mathematical simulation, a building with a green roof would see temperature fluctuations reduced by almost 65% when compared to a conventional roof.
What Impacts on a Living Roof's Thermal Performance?
- Growing Medium
- Composition and thickness of soil, substrate and vegetation
- Roof slope
- Type of vegetation
- Climate conditions
As a general rule the type of living roof matters. Intensive roofs are more energy efficient when it comes to heating and cooling cycles than extensive roofs. And the variables associated with the types of roofs can have a substantial impact. In Singapore, the energy consumption of a building varied from 1 – 15% when the soil thickness, substrate moisture content of and plant type was altered.
This is because intensive roofs tend to require a larger growing medium to support the larger plants and trees associated with intensive rooftops. This study comparing data from 4 North American climates suggests that the optimal substrate depth for living roof insulation is around 15cm. Which is much more indicative of an intensive rooftop.
And the same study suggests that for cooling heat-dominated cities, a plant height of 30cm is optimal. Whereas for retaining heat, smaller plants of around 10cm is ideal. And plant density and coverage must be taken into account here too. For retaining heat, shorter, denser plants are ideal. Hence why sedum dominated extensive roofs can be so effective.
Living Roofs Heat Regulation in the Winter
A green roof’s ability to retain heat makes them an excellent, natural property insulator in the winter months. Whilst they are more effective in the summer months, they insulate properties effectively in both warm and cold climates. As the above studies attest to.
The plant and substrate thermal mass substantially reduces heat loss. Which means two things:
- You will reduce your GHG emissions and your carbon footprint – something we should all be looking to do
- You’ll reduce your energy bills
Which given the millions of us about to be hit by rising energy bills is most definitely a good thing. If you want to create an effective green roof for the winter months, make sure you plant perennials – plants that flower effectively in colder months.
This will help with insulation AND prevent your roof from looking awful. This guide to building a green roof should help.
Living Roofs Heat Regulation in the Summer
And their ability to retain heat in the winter is effectively reversed in the summer months. The substrate and vegetation shade and protect the underlying roof structure from sunlight, thereby reducing its temperature.
As the mass provides a thermal effect, it also reduces a building’s ability to absorb heat, as the vegetation reflects it. Sunlight typically used as energy to heat the building (with a conventional roof) is otherwise used in the evapotranspiration process, resulting in latent heat loss. Neat isn’t it! And the moisture present in the plants is evaporated, providing additional cooling.
And this isn’t just relevant to your own property. Living roofs have been proven to reduce the urban heat island effect in multiple cities across the world.
In fact, London’s UHI can cause the city to be 10 degrees Celsius warmer than the surrounding areas. And the issues are not just temperature related. It increases energy costs, air pollution levels, heat-related illnesses and mortality rates.
And living roofs been proven to reduce the urban heat island effect by over 2.5°c. A potential London-based saving of 25%.
Green Roofs and Sound Insulation
The combination of substrate, vegetation and air embedded with the living roof system provides effective sound insulation too. Essentially sound waves are either absorbed or reflected.
When comparing the performance of living roofs vs conventional – or grey – buildings with green roofs saw the noise level reduced by 20dB for both intensive and extensive green roofs.
That’s a 22% reduction in noise pollution.
Green Roof Insulation FAQs
Yes green roofs work in the winter. They reduce heat loss from your property – the amount of which is dictated by your climate conditions, substrate and vegetation depth and the slope of your roof.
Well in colder conditions yes. Green roofs insulate a property really effectively in the winter months by mitigating heat loss.
But they are also very effective at mitigating heat gain the warmer months. So whilst a green roof can be considered a warm roof in the winter, it’s most definitely a cool roof in the summer.
Yes living roofs cool houses in the summer through evaporation and evapotranspiration. The sun’s energy gets redirected from heating your property – as happens with a traditional roof – is used in the evapotranspiration process. And heating the moisture present in the plants results in further heat loss.
But in the winter months, green roofs trap heat in your home much more effectively than conventional roofs.
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