b'GREEN ROOF POLICYin some green roof systems), growing media composition and blends and plant species selection.One more thing about standards. Standards live in the world of must and shall. They are not recommendations, though guidelines (sometimes called recommendations) often comple-Its Chaos ment standards. Standards necessarily take a position; guide-lines and recommendations do not. If green roofs are going to Without Us succeed and flourish, only standards will carry them toward success. Guidelines are for pirates.For green roofs to succeed, they should be built from materials that have been pre-screened for their performance characteristics. That means each product must be scrutinized to ensure it has suceeded in the marketplace Great MaterialsThe marketplace is bursting with materials that claim to be the best for a waterproofed roof, or the best for a green roof system. But not all materials perform equally, and not all are well-suited to every roof platform or the living systems it supports. For green roofs to succeed, they should be built from materials that have been pre-screened for their performance characteristics. That means each product must be scrutinized to ensure it has succeeded in the marketplace, and that it meets or exceeds the basic testing and manufacturing standards by which material integrity can be objectively measured. The RoofStar Guarantee Program succeeds admirably on this front for roofing.Objective material standards can be applied to the array of green roof materials in the marketplace, to govern plant selec-tion,growingmedia(mixing,amendments,dryweightand waterretentioncapacities),rootbarriersanddrainagelayers (thereareASTMtestmethodsforthese),andwind-resis-tance capabilities. A wealth of green roofing experience over the past two decades also defines what works, and what is just marketing fluff. ProfessionalsGreen roofs are too important to be built by amateurs. They must be built by contractors who are qualified and professional. Great materials installed in line with objective, clear and rational standardssucceedwhentheyareputtogetherbymenand women who have been trained and qualified. No good roofer is born with the gift; he or she has to develop ithabits of work-manship formed by the repetition of skills acquired through excellent training. Trained professionals can demonstrate their 26lROOFINGBC l FALL 2019'