Do I have to worry about a root-resistant protective layer if I only have an extensive greenroof with nothing but sedums?
Yes! Just because you design a greenroof with tiny horizontal roots, it doesn t mean you can t get a surprise plant with a huge taproot looking for water however they can get it. Seeds come in from many sources the wind, and from those beautiful birds that you love seeing on your greenroof so much. I have seen oak and maple seedlings growing in of rotted compost on a pitched roof, for example. And, believe me, those roots will seek water wherever possible in times of drought way into the asphalt membrane! If your roofing membrane is organic in nature asphalt, asphaltic bitumen, etc., you need a root barrier, it doesn’t matter how low growing your extensive greenroof plants are. It needs to be a dense inorganic material that inhibits root penetration, like polyethylene. This protective layer can be a heavy duty pond liner (EPDM, etc.) or other non-organic element that contains an injected root repellent, such as a copper element. Also, many North American drainage products bypass a sepa
