Green Sense?

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Author Message Russell W. Wood, CSI, CCS Senior Member Username: woodr5678 Post Number: 146 Registered: 11-2003 Posted on Thursday, October 08, 2009 - 04:09 pm:    We are more than aware of the potential benefits of vegetated green roofs. However, on the con side we're in south Florida, with insects, critters, heat, humidity, heavy rains, hurricanes (building envelope elements must withstand 145 mph winds per code), etc. Have any of you worked on projects with veggie roofs & does anyone know of any such roofs in S. Florida? John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1117 Registered: 03-2002 Posted on Thursday, October 08, 2009 - 05:37 pm:    Never in South Florida, but we have done quite a few in New England. Insects, heat, humidity and rain should not be a problem if designed properly. The systems should use plants that do not need irrigation, as this defeats much of the purpose of the roof. Nor will they have standing water for insects to breed in, though I suppose they will otherwise be there as much as any natural environment. Nor should heavy rains be a problem. Systems can be design to absorb water, then drain from below the planting medium as well as take some surface run-off. Hurricanes are another question. You can't assume the vegetated roof will hold your roofing system in place. I don't know how the industry is responding to the idea that the growing medium and plants may become airborne. FM has written some things about that, I believe, you might check them out. John Hunter Senior Member Username: johnhunter Post Number: 74 Registered: 12-2005 Posted on Thursday, October 08, 2009 - 07:27 pm:    FM Loss Prevention Data Sheet 1-35, Section 3.0, notes that geographic locations of green roof systems are limited based on wind speed (3 second gust) as determined by Data Sheet 1-28 Design Wind Loads. Joel McKellar, LEED AP Senior Member Username: joelmckellar Post Number: 42 Registered: 02-2006 Posted on Tuesday, October 13, 2009 - 03:23 pm:    I've never gotten a satisfactory answer out of a green roof rep about compliance with uplift testing (I'm based in Charleston, SC... generally 130 mph) "It'll be fine!" is the normal response. In their defense though, how bad could a bunch of dirt and sedum flying off a roof really be? Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 224 Registered: 10-2007 Posted on Tuesday, October 13, 2009 - 03:28 pm:    Loose ballast on roofs has been a common source of projectiles when subject to hurricanes. These rocks have been the source of damaged glazing on adjacent glazing. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1120 Registered: 03-2002 Posted on Tuesday, October 13, 2009 - 04:48 pm:    The problems Mark notes is one reason for the development of the small missile impact test for hurricane zones. How much damage flying sedum or planting medium causes I couldn't venture to guess. Scott Mize Senior Member Username: scott_mize_ccs_csi Post Number: 12 Registered: 02-2009 Posted on Tuesday, October 13, 2009 - 05:44 pm:    I don't think flying dirt and weeds would have quite the same effect as flying river stone...:-) That said, I think the "green roof vs. hurricane" issue depends on a couple of things. First, what type of "green roof" is it? Each of the major types would fail in a different way under conditions of extreme uplift. Probably the least damaging would be the shallow extensive roofs with 6 inches or less of growth medium. The dirt and plants would pretty much just blow off. I would design a roof in this category to withstand the wind uplift without counting the green roof. I think the modular systems are similar. The uplift would have to be severe enough to overturn one full tray, but once that starts, they'd probably all go in a domino or cascade effect. This time, you've got weeds, dirt and recycled HDPE trays flying through the air. No too much damage there. Heck of a mess, though... An intensive system with 6 inches or more of soil, drainage layers, etc., starts to look like something heavy enough to stay on your roof. I'd like to see some testing on that, though. And the more I think about it, the more I think you ought to - at least in the hurricane zones - design the roof to stay on the building even after the "green" part of the roof flies away... Thanks for the pointer to the FM bulletin, Mr. Hunter. I'll be looking that up first thing tomorrow. James M. Sandoz, AIA, CSI, CCS, LEED AP Senior Member Username: jsandoz Post Number: 61 Registered: 06-2005 Posted on Wednesday, October 14, 2009 - 02:19 pm:    An HDPE tray in a 130 mph wind can do I lot of damage. If it breakes one window in a building then it is much more likely that other fenestration or doors will be blown out and other damage will ensue. I've seen a galvanized trash can lid hurled through a 1/4 inch glass window during a hurricane like Odd-Job's hat in the Goldfinger movie. Laminated glass wasn't required back then and, even today, is not found in all buildings in hurricane zones. William C. Pegues, FCSI, CCS Senior Member Username: wpegues Post Number: 798 Registered: 10-2002 Posted on Wednesday, October 14, 2009 - 04:10 pm:    We have done a number of vegetated roofing systems from urban to suburban in the Washington, DC area, always hot fluid applied membrane system. We do have a couple projects in early design in FL, so I thought it might be about time to put the question to manufacturers. My American Hydrotech contact responded that they have worked on numerous vegetated roofs in Florida, including Southern Florida. Some have the full system (membrane to plantings and all in between as a single source warranty), some just the membrane with the remainder by other manufacturers (a route I would not personally go). Apparently to do work in Dade County you need a Dade County NOA (Notice of Acceptance) – Hydrotech has 6 assemblies with NOA with some additional testing being completed. The code people permit them as “Extensive Planter’s”, or essentially as toppings over NOA approved assembly. Minimum 6 inch deep growing media depth is required. Hydrotech has a local blend for plant pallets. Sedums are NOT used. They will die immediately due to the wind. Indigenous species are used. Hydrotech states they are currently developing additional plant pallets for the FL market. Drip irrigation required. For me, the prime points in a vegetated roofing system regardless of where located, is a single source warranty capability for the complete system including plants, growing medium and all other components, including a thriving requirement for 50% coverage in 1 year, 80% in 2 years (or greater if they give it), no limitation on movement of 'overburden', ability to transfer the warranty to a new owner. All of this, Hydrotech can give. Henry, depending on how you press them, can do the same, though they really like to partner for their growing medium and plants. They will comply with what I have listed above in the area local to me, but I have not approached them about FL yet. William William C. Pegues, FCSI, CCS, SCIP Affiliate WDG Architecture, Washington, DC | Dallas, TX Scott Mize Senior Member Username: scott_mize_ccs_csi Post Number: 14 Registered: 02-2009 Posted on Thursday, October 15, 2009 - 02:25 pm:    Thanks, James! I probably should have said, "less damage". Thanks, William! It sounds like your experience (and Miami-Dade's rulings) confirm my supposition that a green roof in a hurricane zone should be over a roof assembly that will stay on the building after the green part flies away. David Stutzman Senior Member Username: david_stutzman Post Number: 57 Registered: 07-2002 Posted on Sunday, October 18, 2009 - 10:40 am:    Be careful specifying vegetated roofs in areas with design wind speeds greater than 100 mph if the facility is insured by FM Global. FM data sheet 1-35 for green roofs does not permit vegetated roofs in areas exceeding 100 mph design wind speed. Colin Gilboy Senior Member Username: colin Post Number: 207 Registered: 09-2005 Posted on Friday, October 30, 2009 - 12:13 pm:    Lynn J. asked me to post links to two articles: Design Strategies to Address Wind Scour in Green Roofs in Extreme Wind Areas: http://www.4specs.com/discus/attachments/RS_high_wind_conditions.pdf Design Strategies to Address Wind Uplift and Scour in Green Roofs: http://www.4specs.com/discus/attachments/RS_windstmt_rev2_110207.pdf Colin Gilboy Publisher, 4specs.com 435.654.5775 - Utah 800.369.8008