Dangers of High Organic Matter in Green Roof Media
The photos above of are various projects around New York City. Many owners and architects do not understand the danger that blends with very high organic matter content can present.
Looking at these site photos shows the inherent problem. Media for roofs and planters that is very high in compost quickly end up like this: broken down, shrunken and not functional as a soil or stormwater solution!
A true green roof media has only 10% or less organic matter by mass. Yet, where cost cutting is common and these complex systems are hard to understand, poor quality materials get installed on these roofs. We have personally seen too many installations like this that use primarily compost and mulch. With no aggregate, sands or minerals, these soils are like a potting mix you would buy at the store: light, fluffy and CHEAP. You get what you pay for. It shrinks because the mostly organic material breaks down and doesn’t drain These pictures are only 3-4 years after installation. Naturcycle wants a green roof or planter to last decades, not days! If someone is offering you a very cheap, super light green roof soil that looks like a potting mix, be wary and get the data. Shop around! There are good providers like Naturcycle, but this is malpractice and a HUGE headache for the owner later. None of these materials would meet the FLL Guidelines. Very high organic matter soil blends (more than 10% organic matter in the final soil) are a danger to any project on roofs or at-grade. Naturcycle is here to help and educate owners and landscape architects on the right questions to ask and what to look for on green roof projects of any size.