Vegetated Roof Tops

What are the benefits of installing landscaping on your roof top?

Some of the justifications for having a vegetated roof top include:

• Stormwater Control – green roofs reduce the amount of stormwater flow by absorbing rainwater
• Pollutant Removal - airborne pollutants carried by rainwater can be filtered by green roofs
• Cooling Loads and Urban Heat Island Reduction – green roofs can reduce cooling loads by reducing rooftop temperatures
• Air Quality Benefits – green roofs filter dust and other pollutants out of the air
• Noise Reduction – green roofs have good sound attenuation
• Wildlife Habitat – green roofs attract songbirds, butterflies, and other wildlife
• Aesthetic Benefits – what’s more pleasing to the eye; an old roof membrane or a lush green roof top?
• Enhance Roof Membrane Life Cycle – protecting the membrane from ultraviolet light can extend membrane durability

These are just some of the reasons individuals use to justify putting dirt and plants on their roofs, but I find their logic a bit skewed at times when you consider just how much vegetation it takes to make even a minimal environmental impact. 

As an industry we had done a pretty good job over the past 30-years of directing engineers, architects, and other designers to remove as many penetrations from the roof top as possible.  Now we’re not only using it as a platform for things like photovoltaic power plants, but we burying them under tons of dirt and vegetation.

If you want landscaping on your rooftop that’s fine, but be honest with yourself as to why you’re doing it. In most cases I believe the primary reason people choose to landscape their roof is because it’s a “novel” idea and it makes them feel good; at least initially.

Don’t lose sight of what you’re actually getting into and the effort that it will take to maintain the landscaping. The landscaping is not maintenance free and just like any garden; watering, weeding, and fertilizing will be necessary to keep the “roof” alive. Some plant attrition will also need to be addressed periodically.

Too often this focus on the landscaping overlooks the real purpose of the roof and in particular, the necessity to have a durable and reliable waterproofing system to support the landscaping. Roofs can leak for any number of reasons, but if trouble erupts on a landscaped roof system, finding and fixing the issue is problematic to say the least.

If you choose to landscape your rooftop, be sure to consider the following attributes of the actual roof system that you’re depending upon to keep your building dry:

• Evidence of a long history of performance in harsh environments
• Evidence that the vegetation’s root systems will not degrade or penetrate the roofing membrane
• Evidence that the membrane system has superior chemical resistance against fertilizers
• Evidence for superior resistance against bio mass and/or molds and algae

Simply put, focus on your ROOF first then you can deal with the prospect of landscaping it.