What does a green roof do?

green roofing

Updating Your Roof for the Better

Before we answer what does a green roof do, let’s take a look at what a green roof is! Nope, in this case, it is not the color of paint, shingles, or tile. As defined by Wikipedia, a green roof, also referred to as a living roof, is a roof with vegetation entirely or partially covering a flat rooftop. It is a growing medium that has been planted intentionally on a flat roof that has been prepared with a waterproofing membrane, a root barrier, a drainage system, and an irrigation system. 

What is a green roof made of?

The basic anatomy, listing in layers from the bottom up, are: 

  • Structural Roof Support
  • Vapor Control Layer
  • Thermal Insulation
  • Roofing Membrane Support for Planting
  • Waterproofing
  • Root Repellant
  • Drainage
  • Filter Membrane
  • Growing Medium
  • Vegetation

How is a green roof constructed?

The traditional soil that is in a typical yard garden or a house plant is dense, and after a rain or watering, it becomes tightly packed. This soil type has reduced aeration and water retention for the roots. The growing medium for a green roof is different.

 It is composed of mineral aggregates and a small amount of organic material. A green roof needs to have consistent drainage with aeration, and a structure that allows it to keep water contained. A green roof needs to resist compression and decomposition, remain lightweight, and be chemically and physically stable.

A green roof may be installed in one sizeable unified section and is a green roof without plastic separating the plants. A modular green roof will consist of small movable planting beds with metal or plastic trays housing the growing medium. The portable plant beds are then placed together, creating an extensive green roof. Because a modular green roof is planted in movable planting beds, it can be installed in increments that are removable for maintenance, allowing the root layers to be inspected easily from time-to-time. 

A modular sectioned green roof can be cultivated in a greenhouse and then planted on the green roof when the plants are established. There are fewer issues of any replacement plants that don’t take to root or struggle to thrive. A drawback to modular section green roof plants is the moisture can’t flow between the units, which increases the impacts of dry and wet spells for the plants.

green roof

Do green roofs need maintenance?

For a healthy and thriving green roof, like any other garden, routine and preventative maintenance is recommended. Having somebody in charge that has experience in gardening is always best. Because a green roof is typically on an elevated structure, safety training for anyone that will be tending to the green roof is recommended.

The primary tasks for ongoing green roof care and maintenance are based on the seasonal plant care, aka, the type of medium and vegetation planted, and the regional climate. Basic maintenance of a green roof is the same as a ground planted garden with watering, weeding, and basic plant care, such as pulling off dead leaves. The best measure for a healthy and thriving green roof is proactive maintenance.

What problems do green roofs solve?

Green roofs have been around forever, especially in Europe. They are gaining popularity in America as we have learned they aren’t just for looks, but the green roof benefits we receive may not seem like much, but they do a lot for our environment: 

  • A green roof absorbs heat and provides a natural layer of insulation, which reduces energy costs. A six-inch thick green garden can reduce energy usage by seventy-five percent because it takes less air conditioning to keep a building cool – a big plus for structures in the southern states.
  • A green roof reduces the Urban Heat Island Effect of absorbing and trapping heat. 
  • A green roof removes air particulates and produces oxygen, all while providing shade if there are trees planted in the garden. 
  • A green roof with trees not only provides shade for humans and the plants, but it minimizes the UV rays that shortens the lifespan of the roof.  
  • A green roof can minimize and slow stormwater runoff on to the hard surfaces of urban environments. Typical flooding and pollution because of nonporous surfaces are reduced with much of it absorbed by the green roof plants. 

How long do green roofs last?

A green roof and sustainability are a combination that this country has not taken full advantage of yet.  The estimated lifespan of a green roof is 40 years. That is 40 years of reduced energy needs, which reduces the greenhouse effects on the environment.  Considering the natural increased R-value, a green roof provides, naturally, not humanmade insulation. 

Last Words 

So, which do we get the most benefit when it comes to green roof vs cool roof? They are both beneficial in their way. A cool roof reflects the sunlight and heat, sending it back into the atmosphere. A green roof absorbs the sunlight and heat, keeping it from entering the structure and stabilizing the air to a near ambient temperature.