Green Roof 101: What It Is, Main Types and How to Install One

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a chicago green roof on a building

A green roof is a popular thing in Europe. It has been that way for a while. Still, the concept continues to spread across the world. Germany developed the technology that contractors use today to install these roofs. The technology was embraced in Germany and other European countries quickly but has been slower to spread in the United States.

As more people become aware of the many green roof benefits they’re missing out on, the number of green rooftops in other countries is rising. Over the next few years, the price of installing one of these roofs will decrease, and more people will jump on the trend. Continue reading to learn more about the types of green rooftops, the advantages and disadvantages of these roofs, and what to expect.

What Is a Green Roof?

some plants on a rooftop

A green roof is a rooftop that’s covered in vegetation with a growing environment to provide nutrition for the plants. Homeowners, businesses, and city governments have all shown an interest in this type of roof. An increasing number of people from all walks of life are beginning to care about the environment. And this type of roofing is one way to promote environmentalism.

Green rooftops also enable urban areas to grow some of their own crops. They have greater longevity than conventional roofs, provide insulation for the building, and absorb storm water. Many people find it relaxing to sit on the green rooftop when they need a breath of fresh air, something often difficult to obtain in huge cities.

There are two types of green roofs. An intensive green roof is like an elevated park because it is strong enough to support benches, walkways, shrubs, and trees. Intensive roofs have complex irrigation, structural support, root protection layers, and drainage. Rooftop gardens and other similar simple vegetation setups are extensive green roofs. An extensive rooftop is lightweight in comparison and doesn’t need as much maintenance. Both types of roofs consist of nine important layers: structural support, vapor control layer, thermal insulation, support panel, waterproof layer, drainage layer, filter membrane, growing medium, and vegetation.

Pros and Cons of Green Roofing

a building with a green rooftop

Advantages of a Green Roof

  • Reduces the “urban heat island effect.” On hot days, urban and suburban areas can suffer from the urban heat island effect. This is an increase in temperature that often feels unbearable. The urban heat island effect is caused by heat intensifying on reflective and impermeable surfaces in the city. Green rooftops provide shading and use heat energy to minimize the urban heat island effect. If enough buildings in a city adopt green rooftops, it could prevent the effect altogether.
  • Prices are gradually decreasing. The initial cost of a green rooftop is high, but prices are gradually decreasing as the industry grows.
  • Benefits are greater than the costs. Although green rooftops are expensive, the long-term economic benefits outweigh the initial cost. For one, this type of roof lasts twice as long as a conventional roof. You must factor those cost savings into your cost-benefit analysis.
  • Protects the roof from UV radiation and storms. It will last longer than other roofs because of this extra protection from the elements.
  • Stable surface temperature. Traditional roofs can reach 90ยบ F, but green rooftops stay at air temperature or cooler.
  • It creates a natural insulation. The vegetation on top of the roof provides insulation for the building. It will be cooler inside during the summer, allowing you to reduce the cost of cooling and stay comfortable. A six-inch extensive green rooftop can decrease energy usage by 75% in the summer.
  • Prevents sewer overflows. Green roof systems absorb and filter rainwater for growing the vegetation. Thus, less water makes it onto the streets and in the sewers. This helps prevent sewer overflows and flooding from occurring.
  • Reduces particulate matter that’s harmful and improves air quality. Particulate matter is a mixture of solid and liquid particles in the air. Most of these particles are harmful to human health. Plants remove particulates from the air, so having a green rooftop is beneficial to your health. You won’t breathe in as many harmful particulates.

Disadvantages of a Green Roof

  • It is expensive. The green roof design is pricey because it requires structural analysis, professional design, nine essential layers, and several systems. Moreover, they require extra support to handle the weight as well. Extensive green rooftops usually cost $8 or more per square foot.
  • It is heavy. Green rooftops are heavier than traditional roofs. In order to support this weight, some roofs have to be retrofitted, which adds onto the expenses. Buildings with flat roofs are usually strong enough to handle the weight load of a green rooftop.

What to Expect from a Green Roof

small houses with green rooftops

Just like other roofs, green rooftops must have a system for draining water off the building. Other factors to look for in a good green roof are a light weight, matching its type, root protection barriers, and irrigation.

Intensive green rooftops need at least one foot of growing medium. They usually create a load of 80-150 lbs. per square foot. In contrast, extensive roofs accommodate 15-50 lbs. per square foot. This difference makes sense considering intensive roofs can include walkways, trees, and benches.

Look for a waterproofing warranty when shopping for a green roof. Reputable roofing companies and green rooftop providers offer this type of warranty. If the waterproofing system isn’t good, you could experience drainage backups and root puncture. In addition to confirming a waterproofing warranty is included, check the company’s references. Specifically, check for waterproofing success in their past projects.

Bottom Line

Green roofing is good for the environment, your health, and even the community. The biggest downside to this type of roof is how much it costs. However, the benefits of green rooftops are so plentiful that it easily makes up for the initial expense. They can reduce cooling costs of your home or business by 75% in the summer. On days when you don’t have cooling, it won’t be as hot inside the building either. Sitting in nature is good for your health. When you live in an urban area, a green rooftop gives your mind a bit of healthy greenery to wind down after a stressful day.

Image sources: 1, 2, 3, 4

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