Myths About Green Roofs

Green roofs, eco-roofs, vegetated roofs or living roofs – whatever you want to call them, are sprouting up everywhere, including atop residential buildings.

With their popularity comes some misconceptions and general assumptions. Among them, green roofs are only for eco buffs and they are high maintenance.

This is false, however. A green roof is not just a good insulator; it also helps to reduce heating and cooling costs, and even helps control stormwater runoff and retention.

1. They are expensive

Green roofs are an excellent way to improve your home’s energy efficiency and lower your carbon footprint, but they can be expensive. Their installation costs are higher than shingle roofs, and their lifecycle costs can take years to recoup.

Nevertheless, they are worth it for their environmental benefits: cleaner air, less heating and cooling demands, and reduced carbon emissions. They also help to reduce the urban heat island effect in cities.

The cost of a green roof is usually based on the type of roof and the plants used. Intensive roofs are more expensive than extensive roofs because they require more soil and growth concentrates, as well as more watering.

In addition, green roofs have to be properly designed for drainage and irrigation. They also need a filter sheet above the drainage layer to hold back fine particles of soil. This prevents the soils from washing out.

2. They are difficult to maintain

A green roof will require a lot of maintenance to keep it healthy. This includes watering, feeding and weeding.

It also needs to be able to hold enough water to sustain plant growth during times of drought. This can be difficult in dry climates where the water supply is limited and mains water supplies may not be reliable.

The type of plants that are planted on the roof will affect how much maintenance is required. Intensive green roofs are usually made up of larger, robust plants with deeper root systems than extensive green roofs.

Intensive roofs often need to be fed regularly as they have greater nutrient requirements than small sedums and wildflowers. They also need to be inspected and removed of unwanted self-seeding plants at least once a year.

3. They are not environmentally friendly

Green roofs are an excellent addition to a home or building as they can reduce the energy costs and air conditioning demands. They also help to lower air pollution and greenhouse gas emissions, as well as absorbing moisture from the rain.

The vegetation on a green roof absorbs about 50% of the sun’s heat and can reflect 30%, helping to cool the surrounding environment. This process, known as evapotranspiration, reduces the Urban Heat Island effect and can save you money on your electricity bill.

A green roof can also filter airborne pollutants and carbon dioxide, which can help lower rates of respiratory diseases such as asthma. This is one of the reasons why many cities encourage the use of green roofs.

A green roof can reduce stormwater runoff in urban areas, lowering the risk of flooding and sewer system overflows. It can also help to reduce soil erosion and increase groundwater recharge.

4. They are not good insulators

Green roofs do not provide any kind of insulation.

During the summer, green roofs release moisture as part of their natural evaporation and transpiration process. This helps keep the roof cool and reduces air conditioning costs.

In the winter, green roofs also help to retain heat within a building. The substrate absorbs some of the sun’s heat that would otherwise radiate from a dark building surface, and then releases moisture through the plants as part of their evapotranspiration process.

The thicker the substrate and vegetation, the better a green roof is at reducing noise. In fact, a study at the airport in Frankfurt found that a 10 cm green roof reduced sound levels by up to 5 dB.