Vegetated Roof on a School

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Author Message John Hunter Senior Member Username: johnhunter Post Number: 75 Registered: 12-2005 Posted on Thursday, March 18, 2010 - 08:11 pm:    We are proposing a tray-type vegetated roof (low slope - 1/2 inch/ foot) for a school project in California. The AHJ is the Division of the State Architect (DSA) who have made a correction requiring anchorage of the trays to structure, which we are interpreting as their requiring mechanical fasteners through each tray. There is no way I can think of to comply, nor does it seem reasonable to do so. Has anyone else faced and successfully negotiated a similar situation? Any assistance will be greatly appreciated. Steven Bruneel, AIA, CSI-CDT, LEED-AP Senior Member Username: redseca2 Post Number: 224 Registered: 12-2006 Posted on Thursday, March 18, 2010 - 08:26 pm:    Thinking creatively, you could apply a "soil retention system for steep slopes" like the American Hydrotech system even though you have a low slope application. This consists of baffles connected by stainless steel cabling. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 266 Registered: 10-2007 Posted on Friday, March 19, 2010 - 02:28 am:    If your desire is to have no positive connection between the trays and the structure this is not a battle that you can expect to win. I believe that you will find that there are a number of possible solutions. The code concerns would be to make sure that the trays do not fly off in a big wind and to make sure that the trays do not move about in an earthquake and hurt somebody. Without knowing how the trays are constructed It is hard to give specific examples but this should not be an impossible request. Lisa Goodwin Robbins, RA, CCS, LEED ap Senior Member Username: lgoodrob Post Number: 61 Registered: 08-2004 Posted on Friday, March 19, 2010 - 09:53 am:    As an aside about rooftop trays, I was recently looking at the vegetated trays at the Boston Children's Museum. The trays are really small, like 12 inches square maybe. Not only are the plants all dead (yes it's March in Boston), but the trays don't sit flat either. The green roof is designed to be seen from inside the museum, but the effect is probably not what was intended. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1180 Registered: 03-2002 Posted on Friday, March 19, 2010 - 12:11 pm:    We've decided that the supposed benefits of trays are outweighed by the viability of the plantings in them. That is, non-tray systems are going to perform better because the plants thrive. As to fastening them down, perhaps they can be fasened together, which would give them more wind resistance. It may be possible to come up with a way to adhere or weld a tab to the roof mebrance (non-penetrating) that is then used to hook on to the trays. Seems fussy. Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 939 Registered: 07-2002 Posted on Tuesday, March 30, 2010 - 07:14 pm:    the other thing is that if the wind is high enough to blow trays off the roof -- its probably high enough to dry out the trays as well. Usually the trays anchor to each other with clips, which makes them a bigger thing on the roof but I don't know of any system that anchors them to the roof itself. Talk with the American Hydrotech guys. they warrant from the deck up, and have systems for a lot of windspeeds and conditions.