Green Roofs and Climate Change in 2021
Energy-efficient designs like green roofs can play a major role in mitigating climate change over the next few decades.
Their ability to reduce carbon emissions, minimise pollutants, and improve human health make them a standout contender for the most underutilised resource in the fight against global warming.
With our planet under imminent threat from ever-increasing pollutant levels, using otherwise empty urban rooftops to combat it should become a priority.
How Can Green Roofs Reduce Climate Change?
In densely built-up areas where providing ground level green spaces may be impossible, living roofs are an achievable green option.
These roofs not only mitigate the urban heat island effect but also act as insulators. Insulating buildings to mitigate heat-loss in the winter and minimising heat-gain in the summer. So you can reduce your energy bills and carbon emissions throughout the seasons.
Top 6 Ways Living Roofs Can Help Climate Change
Green roofs play host to a host of economical, environmental and mental benefits. But when discussing how they impact climate change, we will hone in on the environmental
- Reduced carbon footprint
- Mitigating the urban heat island effect
- Improved heating and cooling cycles
- Reduction in energy consumption
- Flooding prevention
- Reduction in air pollution
Reducing your carbon footprint
Green roofs mitigate your carbon footprint directly in two primary methods.
As plants photosynthesise they take in sunlight, water and – importantly here – carbon dioxide to create energy and oxygen.
- Reduction in energy usage
By improving the energy flow – in both heating and cooling cycles – throughout buildings, living roofs minimise the use of air conditioning and heating.
On top of this reducing urban temperatures, flood risks and both air and noise pollution indirectly contribute to reduced carbon emissions.
Mitigating the urban heat island effect
An urban heat island is a metropolitan area that is significantly warmer than its surrounding area(s). As cities replace rural areas with high concentrations of concrete focused structures (surfaces that absorb and retain heat), the average temperature increases.
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.
Improved heating & cooling cycles
Green roofs consistently reduce the average daily heat flow, particularly in the summer. They provide excellent insulation throughout the seasons.
A living roof’s thermal effectiveness can reduce air conditioning usage by as much as 75%.
And whilst they’re certainly more effective in hotter months, their ability to retain heat in the winter make them a year round winner.
Hydrofluorocarbon (HFC) is the primary refrigerant used in air conditioning, and it traps 1430 times more heat in the atmosphere than carbon dioxide per unit of mass.
The global demand for air conditioning is increasing and minimising the quantity of HFCs emitted into the atmosphere is paramount. Green roof’s are a fantastic way to do this.
Reduction in energy consumption
Green roofs reduce heat fluctuations through the roof, leading to decreased energy demands. Because green roofs cool the air around them, this means the air conditioning doesn’t need to work as hard to keep buildings cooler, which in turn saves energy and energy costs.
The growing medium and plants on green roofs provide shading, insulation and evaporative cooling whilst acting as a thermal mass. This reduces thermal fluctuations and energy demands in all-weather conditions.
But green roof are more effective at minimising heat gain than heat loss. Living roofs can reduce heat gain through:
- insulation, evapotranspiration
- thermal mass
However, heat loss can only be mitigated by improved insulation and decreased radiation heat losses. But as air conditioning accounts for roughly 10% of all UK electricity, improving building performance in the summer is essential.
Green roofs help to mitigate flood risk reducing runoff by collecting rainfall. The larger, more intensive the green roof, the greater the reduction in flood risk. Typically extensive roofs intercept and retain the 1st 0.5 – 0.75 inch of rainfall. Intensive roofs can be significantly more.
The water moves through the plants and evaporates back into the atmosphere. The water that isn’t evaporated will still run off, but at a slower pace than a conventional roof.
This lowers groundwater levels and reduces stress on sewage systems during peak flow periods, which in turn helps to mitigate flood risks. This water is in fact cleaner than before. So on top of minimising runoff, the water quality is improved.
In 2050 it is expected that 70% of the world’s population will live in urban areas. As such, making this places as habitable and environmentally sustainable as possible is essential.
Reduction in air pollution
Poor air circulation in today’s metropolitan areas can create stagnant, polluted air blankets. Eco-roofs thereby provide an efficient solution to reduce dust, ozone level, volatile organic compounds, and smog in the city air. And these plant leaves even trap particulates and smog found within urban areas.
Apart from curbing projected emission growth, green roofs can remove harmful air particulates, and produce oxygen through photosynthesis.
When it comes to quantifying the impact a green roof can have, studies in the USA showed that the aboveground section of the plant collected 84g of carbon / m2 .Whilst the roots accumulated 53g of carbon / m2 in one vegetation season.
Therefore the average sized urban UK green roof (around 70m2) could then offset around 50,000g of C02 each year.
And, in terms of sulphur dioxide – a noxious, acidic gas is primarily produced from the combustion of coal or crude oil – green roofs
And research in Singapore showed that the substrate and vegetation could capture up to 37% of S02 from the air. A gas very much associated with:
- Respiratory conditions
Primarily in the form of asthma and chronic bronchitis.
Sulphur dioxide combines with water vapour to form acid rain that may be transported large distances and cause substantial damage to man-made structures particularly.
Whilst the UK’s sulphur emissions have decreased significantly in recent times, the CLRTAP and the NECR aim to reduce SO2 emissions even further.
Green Roofs & Climate Change FAQs
Yes green roofs help with climate change. The growing medium and plants have pollutant absorbing, temperature controlling properties that can help control urban climate issues.
Numerous countries and cities around the world have reaped the rewards for their energy-saving and pollutant mitigation properties.
In multiple ways. Firstly plant photosynthesis takes in harmful, temperature raising greenhouse gases and emits oxygen in the process.
Secondly the green roof’s growing medium’s ability to insulate houses – in both summer and winter – reduces the energy demands associated with heating and cooling. Reducing energy usage and emissions.
Yes living roofs absorb carbon. They do this primarily via photosynthesis.
As the plants photosynthesise, they take in carbon dioxide (among other gases) and convert it to energy, emitting oxygen in the process.
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