The Accidental Green Roof

  • Ernie Cecchetto

Green roof systems help reduce the “Urban Heat Island Effect”, have stormwater retention capabilities, and can extend the service life of the underlying roof membrane by protecting it from some environmental conditions (UV rays, etc…).

But what if your roof wasn’t intended to be green? What happens when a roof has unwanted plant growth?

During my 20+ years in the business…I’ve observed some great feats of nature. I’ve seen weeds growing out of patio stones (not through the joints…literally out of the deteriorated stones themselves), I’ve viewed fruiting vines growing from drain assemblies, 10’ plus trees growing up through gravel ballast and my absolute favourite… a blueberry bush growing on the top of an HVAC ducting system.

How does this happen? Well, I’m not a horticulturist by any stretch…but based on the variety of birds I’ve also viewed on roof systems, I’d say they have a lot to do with it!

So what’s the harm in a few plants flourishing on your built-up or inverted roof?…well, in a nutshell, it means you are exposing your roof components to a living / organic entity that is going to use every resource possible to root into your roof assembly and hang on for dear life. That’s right, it’s going to use your roof components as its growing medium. Now if you ever had a tree growing in your yard and didn’t like the fact that the roots were affecting your foundation, paved driveway or interlock stones…imagine what that same fledgling plant is doing to your waterproofing system?

Should you grab hold of the stalk and tear it out you ask?…no, I wouldn’t recommend that.

Toss me an email if you’d like to know how to deal with unwanted vegetation on your roof…or leave a comment with your best “Accidental Green Roof” story.