Smart Material Choices Can Prevent Garden Roof Problems

The Hanging Gardens of Babylon, considered one of the seven wonders of the ancient world, are perhaps one of the most well-known garden roof applications in history. While green roofs today may not carry the same element of wonder as Babylon’s take on design, garden roofs are gaining in popularity in urban neighborhoods across the world.

Advantages of Garden Roofs

Proponents of green roof installation point to benefits derived from properly installed and maintained garden roof systems. A few of these benefits are:

  • A garden roof lowers urban air temperature by a heat-transfer mechanism known as evaporative cooling, diminishing the heat island effect
  • A green roof cools the roof and the building beneath it, reducing utility costs overall.
  • A green roof can last longer than a conventional roof if properly maintained, because green roofs are, to some extent, protected from the most harmful effects of the elements.
  • An eco-friendly option, green roofs work to reduce air pollution and greenhouse gas emissions, help filter pollutants from rainwater, and create a wildlife habitat.
  • A green roof provides sound reduction from rain, hail, or foot traffic.
  • Green roofs designed to accommodate foot traffic, can provide a place for people to enjoy nature and even enjoy the benefits of a small vegetable or herb garden.

Garden Roof Problems and Pitfalls

While garden roofs can provide all of these benefits, sometimes garden roof failures and problems result in major complications and expense for building owners. For the most part, problems and failures with garden roofs rest on two important considerations:

1) Moisture and leakage issues

2) Weight issues

Both of these issues can be addressed by using the proper materials and installing those materials according to specific manufacturer guidelines.

Moisture and Leakage Issues

Perhaps the most concerning issue for those considering a green roof installation is the thought that green roofs are more susceptible to leaking than their more traditional counterparts.

Evidence does not actually support this theory. The fact is that all roofs, if not properly installed, are susceptible to leakage issues. All roofs must have a proper waterproofing membrane.

Of course, green roof installation requires more than the standard waterproofing measures. Because garden roofs must be designed in such a way that they retain a certain amount of water for irrigation of the vegetation, there will ideally be some water on the roof. Waterproofing designed to simply channel water off the roof will not suffice in the case of a garden roof.

Contractors installing garden roofs must use a series of products to achieve good results in terms of water retention, runoff of excess water, and prevention of drainage clogging caused by soil particle erosion.

Dörken Systems offers a green roof system that addresses these issues in a cost-effective, installation-friendly way. Installation of this system involves a number of steps and products. Here is the general order of installation to achieve the best results:

  • Basic roof waterproofing must be installed.
  • After waterproofing has been installed and tested for effectiveness over a 24-48 hour period, a root barrier must be installed. This barrier acts to prevent the roots of vegetation from penetrating the waterproofing barrier and causing leakage issues.
  • Once the root barrier is in place, a perforated drainage board, such as Delta®-FLORAXX can be installed. A proper drainage board provides high compressive strength, large water capacity, and perforations to allow for run-off of any excess water.
  • A geo-textile layer which acts as a filter fabric is then added. This keeps the water retention cups and the drainage space clear of all debris, thus reducing the likelihood of drain clogs.
  • Once all these layers are in place, the growing medium may be added and vegetation may be planted.

Weight Issues

Weight issues typically arise due to improper engineering calculations or installation procedures. It is especially important that weight calculations must include the weight per square foot for:

  • The installation materials themselves
  • The water that will be retained in reserve within the roofing system
  • The soil and particulate matter
  • The vegetation itself
  • Proper calculation of water weight is of particular concern. Using lightweight products designed to prevent excessive water retention will go far toward eliminating weight issues.

The Bottom Line

Garden roofs are increasingly attractive to builders and property owners in urban areas because of their many benefits. To achieve the best results from a rooftop garden, professional installation of materials specifically designed to prevent the problems of excessive weight and moisture and leakage issues is essential. Learn more about our exclusive garden roof system.