Negative Pressure Roofing Systems

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Author Message djwyatt (Unregistered Guest) Unregistered guest Posted on Thursday, June 13, 2013 - 10:26 am:    Has anyone specified a negative pressure roofing system? The most prominent manufacturer/designer of this system is the 2001 Company, Inc. of Waterbury, Connecticut. The engineering principles appear to be sound. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1509 Registered: 03-2002 Posted on Tuesday, June 18, 2013 - 04:03 pm:    David, I'm not sure what you mean by this. All roof systems are subject to some negative pressures and most systems are tested to various "uplift" requirements based upon the physical configuration of the building, wind speed zone, and surrounding topography. Can you elaborate? djwyatt (Unregistered Guest) Unregistered guest Posted on Tuesday, June 18, 2013 - 04:34 pm:    Apparently, the negative pressure system is secured only at the perimeter, the rest being loose-laid (I can't imagine how the mod-bit versions of this idea work, but the literature claims they do). Relieving vents installed at the perimeters result in negative pressure within the system during storms, which purportedly suck the membrane tighter to the substrate. The 2001 company has a powerpoint on its website that seems to have all of the physics and science on this figured out. ken hercenberg Senior Member Username: khercenberg Post Number: 535 Registered: 12-2006 Posted on Tuesday, June 18, 2013 - 04:49 pm:    I've seen several systems like this since the 70's. In most of them, the vents were not properly designed and ended up creating roof leaks, especially during periods of snow and wind-driven rain. All of them sounded good; none of them worked. Perhaps this one does. None of those who used to offer similar systems does anymore that I know of. Several manufacturers who specialized in this type of system are no longer around. Perhaps these folks have found the answer. I agree that the logic is sound. The question is whether it works in reality. They sure seem to believe in it. ken hercenberg Senior Member Username: khercenberg Post Number: 536 Registered: 12-2006 Posted on Tuesday, June 18, 2013 - 04:56 pm:    My understanding of their system was that they advocate essentially a fully-adhered system with vents to reverse the negative effects of wind uplift. Their premise is to suck the membrane down instead of allowing the combination of positive pressure below and negative pressure above from lifting the membrane off. I know a number of roof consultants who advocate simply installing the membrane tight to the deck or, in northern climates, providing a vapor retarder that serves as an air barrier beneath the insulation and membrane to limit positive pressure applied from underneath. FM's RoofNav certainly has numerous tested systems that can meet high wind uplift pressures. I don't recall whether 2001 has any FM listed systems or not. J. Peter Jordan Senior Member Username: jpjordan Post Number: 578 Registered: 05-2004 Posted on Tuesday, June 18, 2013 - 07:25 pm:    I remember seeing such a roof membrane about 10 years ago and wondering if I really wanted to specify a roof that sucked. Lynn Javoroski FCSI CCS LEEDŽ AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 1652 Registered: 07-2002 Posted on Wednesday, June 19, 2013 - 10:24 am:    "Nothing sucks like an Electrolux" Paul Gerber Senior Member Username: paulgerber Post Number: 152 Registered: 04-2010 Posted on Wednesday, June 19, 2013 - 05:08 pm:    I've seen a few spec sections for roofing that have sucked, but it didn't necessarily have anything to do with the Products that were specified! LOL Personally, I've never spec'd a roof system that sucked, Electrolux or otherwise. Ride it like you stole it!!! John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1510 Registered: 03-2002 Posted on Thursday, June 20, 2013 - 02:49 pm:    Assume a metal deck that allows the pressure in the interior of the building to approximate that just underneath the roof membrane. Some storm conditions actually cause the building interior to become pressurized, such as when fenestration fails, loading dock doors are open, etc. Such a "negative pressure" roof system would have to be able to accommodate these positive interior pressures as well as the negative ones imposed on the top surface of the roof membrane. I'm skeptical. I'd have to see FM uplift tests for this kind of condition; or maybe this membrane's use is limited to certain building configurations. J. Peter Jordan Senior Member Username: jpjordan Post Number: 580 Registered: 05-2004 Posted on Thursday, June 20, 2013 - 05:23 pm:    If I remember correctly, there were vents that utilized the negative pressure caused by the venturi effect on the field of the roof. As the wind blew across the roof and tried to lift the membrane off the roof, it also caused the roof vents to "suck" the air from underneath the roof membrane as well (thus the nickname "the roof that sucks"--surely not embraced by the manufacturer). This would supposedly create enough of a negative differential in pressure to negate the uplift. I was intrigued with the theory and saw one that was installed on a building in the Houston Galleria area, but was always skeptical. I do wonder about water infiltration and if there would ever be a situation where the required pressure differential did not materialize. I like the idea of FM testing. Do not know if one exists.