Membrane Roof Recomendations for Plaz...

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Author Message Brian Payne Senior Member Username: brian_payne Post Number: 252 Registered: 01-2014 Posted on Monday, January 03, 2022 - 10:20 am:    Anyone have any recomendations. We typically do rubberized asphalt, but in this case are staying away from those products because of the CLTs. Thoughts? David L. Heuring, AIA, CCCA Senior Member Username: daveh Post Number: 8 Registered: 04-2020 Posted on Monday, January 03, 2022 - 10:51 am:    Brian- see if you can open this design guide- maybe it will be helpful https://www.fpl.fs.fed.us/documnts/pdf2013/fpl_2013_glass001.pdf David L. Heuring, AIA, CCCA, LEED AP, NCARB Ronald J. Ray, RA, CCS, CCCA, CSI, SCIP Senior Member Username: rjray Post Number: 206 Registered: 04-2004 Posted on Monday, January 03, 2022 - 10:57 am:    Brian, I think hot- or cold-applied rubberized asphalt is a good approach for a plaza deck, even with a wood roof deck. If a WUFI analysis has determined that a vapor retarder is required as part of the roof assembly, a self-adhering vapor retarder compatible with the roofing membrane would protect the wood deck. If a vapor retarder is not required, one could mechanically attached a asphalt base sheet, or a vented base sheet, over the wood deck prior to installing the roof membrane. If you prefer another type of roof membrane, any single ply or modified asphalt membrane of your choice, would work. Ron ken hercenberg Senior Member Username: khercenberg Post Number: 1424 Registered: 12-2006 Posted on Monday, January 03, 2022 - 11:08 am:    Taking a quick look at one manufacturer's list of acceptable deck assemblies - https://www.hydrotechusa.com/waterproofing/assemblies it appears that "wood plank" can be an acceptable substrate. Perhaps a short phone call with their technical folks can resolve this for you. Greta Eckhardt (Unregistered Guest) Unregistered guest Posted on Monday, January 03, 2022 - 11:15 am:    This application is really for a waterproofing (not roofing) membrane, and the presence of wood below it makes it very important to use the most reliable waterproofing membrane available. I agree with Ron that rubberized asphalt would be the product of choice. Since it is typically applied to a concrete surface, I think a cement board substrate would be needed over the CLT, or I think it is also possible to pour concrete over CLT. Perhaps a gypsum-based layer will be needed somewhere for fire-resistance. Before discounting this excellent type of membrane, do contact American Hydrotech or another manufacturer to see what they recommend, and what assemblies have been tested for fire performance. And I realize that this may not always be the specifier's role, but you could also ask why they are using CLT in this application. If a concrete deck would provide the most durable, best-performing substrate for this plaza deck assembly, then is that not far more sustainable than calling for a trendy solution that supposedly "sequesters carbon" but may be causing deforestation and meanwhile could be damaged by moisture? James Sandoz, AIA, CSI, CCS Senior Member Username: jsandoz Post Number: 340 Registered: 06-2005 Posted on Tuesday, January 04, 2022 - 09:45 am:    Is the CLT roof deck exposed on the underside? That is about the best reason I can think of to use CLT. In any case I think Ronald's and Greta's advice is good. Brian Payne Senior Member Username: brian_payne Post Number: 253 Registered: 01-2014 Posted on Tuesday, January 04, 2022 - 10:17 am:    Thanks everyone. The office building is a mass timber project with a few small-ish balconies, so changing to another substrate is not really possible. I believe the concern was having a hot kettle on a wood deck. A CBB or concrete topping slab is a possibility, but since the structure is flat, we would either need to slope the topping slab or use tapered insulation which lends itself well to a single ply install. Ronald J. Ray, RA, CCS, CCCA, CSI, SCIP Senior Member Username: rjray Post Number: 207 Registered: 04-2004 Posted on Tuesday, January 04, 2022 - 11:09 am:    The waterproofing or roofing discussion has been around for a while. It is a decision either the architect or building code official needs to make. Personally, I would consider it roofing. In the IBC, “roofing” has different requirements that waterproofing, one of which is wind uplift resistance. FM Approvals’ RoofNav no longer list wood decks as part of an approved system. However, SPRI’s DORA does include wood roof decks using the same testing protocol historically accepted by FM Approvals. I doubt that DORA has wind uplift listings that include a cementitious backer board substrate, although some roof manufacturer may have tested such a system to meet the FM’s VSH hail-resistance rating. Regarding the use of tapered insulation, with the proper cover board, this would be an acceptable substrate for hot- or cold fluid-applied roofing membranes. ken hercenberg Senior Member Username: khercenberg Post Number: 1425 Registered: 12-2006 Posted on Tuesday, January 04, 2022 - 11:38 am:    Actually by Code Deborah is correct, it is technically waterproofing. That is also the reason why no slope is required. If it's roofing you'll need slope. I've asked my Sika Hydrotech golden rep, Matt Carr, to weigh in on this. Looking forward to their reply. Paul Sweet (Unregistered Guest) Unregistered guest Posted on Tuesday, January 04, 2022 - 12:59 pm:    Will there be pavers, which could resist uplift, over the membrane? Brian Payne Senior Member Username: brian_payne Post Number: 254 Registered: 01-2014 Posted on Tuesday, January 04, 2022 - 01:42 pm:    Yes, Concrete pavers and pedastals. Just got off the phone with my Hydrotech rep as well and he's going to do a bit of research, but his off the cuff opinion was there should be no reason why we can't stick with Hydrotech. On the roofing vs waterproofing conversation...it may technically be waterproofing, but I have always found the waterproofing spec sections to be less than what I need and have stuck with the roofing spec for several years now. I get reminded of my recision by my waterproofing consultants on most every job, but it gets built right no matter. Phil Kabza Senior Member Username: phil_kabza Post Number: 696 Registered: 12-2002 Posted on Wednesday, January 05, 2022 - 05:02 pm:    Whichever membrane you select, strongly consider one that is compatible with a leak detection system. You could get a long way toward damaged CLT substrate before occupants noticed a leak. Leaks will occur at the balcony / building interface. You want a Swiss watchmaker on the team to handle the flashing there. Phil Kabza FCSI CCS AIA SpecGuy Specifications Consultants www.SpecGuy.com phil@specguy.com ken hercenberg Senior Member Username: khercenberg Post Number: 1426 Registered: 12-2006 Posted on Monday, January 10, 2022 - 11:00 am:    This is from John Hamati, American Hydrotech, jhamati@hydrotechusa.com: "Hydrotech’s HRA, MM6125-FR has been applied on multiple CLT projects around the US and North America. I believe the largest CLT deck in North America just finished (or in the final stages of) receiving Hydrotech’s waterproofing assembly. This substrate is growing in popularity and we are seeing it more often now. Based on the industries’ feedback and what we have experienced; CLT structures can be susceptible to moisture and dimensional changes. Hydrotech does recommend the addition of cement board, gypsum sheathing, or plywood boards above the CLT and have it properly fastened to it. Other projects utilized a layer of CIP concrete. MM6125-FR is then properly applied over that." Keep in mind that if you put sheathing over the CLT you need to treat the joints. Only the reinforced 215-mil systems can be used. Hydrotech has a Mass Timber Construction brochure that has some useful technical content. I've asked for a link. ken hercenberg Senior Member Username: khercenberg Post Number: 1427 Registered: 12-2006 Posted on Tuesday, January 11, 2022 - 03:56 pm:    Here's a link to Hydrotech's brochures https://www.hydrotechusa.com/resources/resources.php?page=2&category=Brochures. The mass timber brochure is on the second page of available links.