Questions about when V2T can be used
What size roof qualifies for V2T?
There are no minimum or maximum sizes that specifically exclude a job from being a good V2T candidate. However, and for example, 3,500 square feet does not generate enough of a wind profile to work as efficiently as larger roofs. Also, customers typically do cost comparisons of V2T vs traditionally adhered systems. V2T stays pretty close to traditional systems cost-wise on roofs under 10,000 square feet. The real advantages begin kicking in at that 10,000 sf size where you begin seeing increasing labor savings. It is much easier to install a loose-laid membrane than to mechanically fasten, adhere, or ballast such large roofs. Thus, the larger the roof, the greater the savings.
How many vents do I need per roof?
There is no set rule for determining the number of vents based on square footage. Our engineering process carries a PE Stamp and is verified by UL testing and approvals. Each project is different and our engineers consider many relevant variables to determine both the quantity and placement of vents. Some of these include: building and occupant safety, local codes, roof size, shape, height, the direction the building faces, elevation, and local wind speeds.
What deck types work best with V2T?
Most commercial low slope roofs work well. Concrete, tectum, gypsum, and metal decks tend to be the most popular, and easiest.
- If it is a recovery over either tectum or gypsum there is not a problem using the system since there is already a relatively airtight system to install the V2T System over. However, if there is a tear-off to the deck, then it is important that the decks are sealed before installing the system.
- It is important to make sure that the concrete deck is air tight. Installers need to make sure that there are not any openings in the deck that could compromise the air seal from underneath.
- Bare wood and metal decks are more challenging because they are not inherently airtight. In order to achieve a proper air seal, an air/vapor barrier must be included in assembly.
- Hip roof systems are not suitable for the vent application because of the slope. Modifications would be necessary in the mounting process to take advantage of the wind.
Do solar panels work on a V2T roof?
Yes – though this is job specific. Solar panels are complicated because they can be rack mounted, ballasted, or adhered to the membrane, all of which can impact the operation of the vent system depending on how the solar array is configured. The size of the roof will play a role, and if it is larger there is more room to utilize both V2T and solar together.
Vent Specific Questions
How does the V2T Roof System differ from 2001 (Kelly)?
The difference lies in the curved domes of the hourglass shape which add centrifugal force as well as the smaller area between the domes which adds to the pressure created by the wind. Find more information here: https://www.v2troofsystem.com/v2t-vs-the-alternatives/
How does the V2T Roof System differ from turbine vents?
The primary difference here relates to the the materials used and the movable parts. Turbine vents use the wind to create motion which then generates the negative pressure under the membrane. But that introduces the possibility of mechanical failure, which then jeopardizes the building. V2T creates negative pressure by its shape alone – eliminating the possibility of mechanical failure. Read more here: https://www.v2troofsystem.com/docs/V2T-Roof-Venting.pdf
Can I have the vents in white?
The vents can be spray painted on site. The color does not affect performance. Just make sure to not clog the vents with paint. The airflow needs to remain unrestricted.
Which types of membranes need rings vs welding?
- PVC and Elvaloy membranes are welded.
- TPO and EPDM membranes require rings.
Will my vent break if debris hits it? And if so, will it still work?
- Anything will break if hit with enough force. Fortunately, separation of the upper and lower hemispheres does not cause any serious consequences in system performance. The hemispheres working together are what accelerate the wind speed moving through the vents and create a negative pressure. However, without those curves working together, an open vent would equalize the pressure and still keep the roof in place.
- In a real world example, we actually had 3 vents clipped by an electrical chase during a hurricane. The three that were hit came apart at the leg connection and continued to work (albeit at a diminished capacity). The owner called to say that three vents (just the top halves) wound up in the parking lot and was completely impressed that not only was his roof still intact but no serious damage occurred. In addition to the vents being damaged, numerous cuts were made in the membrane from the electrical chase. Their roofing contractor was called in to replace the top half of each unit and fix the cuts, and all was well.
How do tears in membrane affect performance?
- The tear issue has been examined in several research projects and in two real life situations. The first test was conducted at Virginia Tech to determine the impact of air infiltration into the system. To study this, a 1″ tube with a valve in it was inserted up through the wind tunnel floor into the bottom hemisphere. During the experimental run the valve was opened to simulate air infiltration from the interior of the building. At speeds of 144 mph we were only able to impact measured pressures in the vent by .22% which is a negligible change indicating that we have a significant capacity to pull air out of the system.
- The second research project was conducted at IBHS wind tunnel in South Carolina. This tunnel is a 50 million dollar state of the art facility built by 200 member companies from the insurance industry to look at loss mitigating technologies for severe wind events. We tested for two days in the tunnel on a building that was 30′ X 40′ under hurricane force winds with one vent in the roof assembly. When all of the standard protocol tests were concluded we asked if we could blow the roof off by making strategic cuts in the membrane. Through several trials at wind speeds in excess of 100 mph and successive cuts that wound up being a total of 4 feet, we were not able to effect the roof to an extent that it was in jeopardy of blowing off. These cuts measuring 4 feet were oriented to the wind on a 45 degree angle, which meant they were subject to opening up particularly in hurricane force conditions with a loose laid membrane. You can see the full IBHS report here: https://www.v2troofsystem.com/docs/IBHS-Report-for-Vent-test.pdf
- Two roof systems with the V2T technology installed suffered significant tears as a result of mechanical damage during a wind event.
- Roanoke Salem Business Center, a 250,000 square foot roof in Salem, Virginia had an AC panel blow off and tumble across the roof causing at least 12 tears in the membrane with no negative effect to the integrity of the roof system.
- A 60,000 square foot roof in Philadelphia, PA had an Electrical Chase blow off during hurricane Sandy causing a number of large tears in the membrane and clipped three vents; taking off the upper sections. The upper sections were re-attached and cuts repaired following the 70 mph wind event with no membrane detachment.
- Ultimately, each vent on a roof systems acts like small vacuum unit pulling air from the roof system. Once the air has been pulled out the vents keep the roof under negative pressure holding it in place. When you have an event causing a tear, the combined capacity of the vents will act to pull this air out. It has been our experience that it would take a sizable breach to jeopardize system performance.
Can we do a roof in Florida?
- V2T has Florida Building Code Approval and Florida Product approval.
- V2T has not yet been installed in Miami-Dade. It’s important to note for Miami-Dade that the code reads that in the event a PE signs off on a design the building official cannot reject the submission unless they get another PE to refute the document. We suspect it will take some pushing to get it through and we need someone in FL to take on the challenge. For whoever decides to take this on, you would be the first installer in the area and could own the first movers advantage.
Will this system work in high wind conditions?
- We have a number of projects that have been hit by hurricanes, some by several hurricanes, and have no reports of any notable damage.
- The system has a unique design that takes advantage of the aerodynamic flow of air over the roof, which generates a very low pressure under the membrane that holds the system securely in place. This Venturi Principle and a special case of Bernoulli’s Law, allows us to capture the speed of the wind, accelerate it to generate a pressure under the membrane that is lower than the pressure being exerted on the roof from uplift. Because of the physics utilized, the system, when properly sealed, cannot not work. The pressure we generate is proportional to the velocity of the wind squared, so the harder the wind blows the tighter the roof holds.
What membranes are warrantied when installed on a V2T Roof?
- Our manufacturing partners include Carlisle, FiberTite, Flex, and Versico. They all routinely provide 20 year installation warranties. If you have other requirements, let us know.
- In some circumstances we can obtain a third party warranty, though it typically costs more than a manufacturer issued warranty.
Does V2T qualify for a third roof exemption?
This is a tricky one, but it can work. Please note however, that first the building must have a P.E. Structural Engineer sign off on the roof deck that it can support the additional weight. Second there must be an infrared scan of the roof to verify that the roof does not contain too much moisture to remain intact. There are many stringent conditions and are not easily met. So it is possibly, but not an easy process.
Certifications and Approvals
What certifications or approvals does V2T carry?
- V2T is UL Approved.
- FM only tests fully adhered roofs, thus FM is not applicable for V2T (same as it would not apply to ballasted roofs). However, the FM test pressurizes the space below a roof system and blows it off from the inside. The pressure at which the roof fails is the FM rating after applying a factor of safety of 2. We are able to specify roofs according to your requirements exceeding the FM standards. The average V2T roof carries a safety factor of 3.3, which is higher than the FM Global safety factor of 2.
We have installed our roof system on FM insured buildings, but know it can be a very difficult procedure, and approval is not something we can control. If we are simply trying to meet a certain uplift rating based on a specific FM approval code, we can empirically show with PE stamped methodology and backing that the roof will meet or exceed a certain uplift pressure. We cannot guarantee that this will meet with the approval of a particular owner or design professional, but it does meet international building code.
ANSI, SPRI, FMGlobal, ICC IBC
What is ANSI?
The American National Standard Institute (ANSI) is a non-profit organization that administers and coordinates a voluntary standardization system.
What is SPRI?
SPRI, (Single-Ply Roofing Industry) is a non-profit trade association representing the sheet membrane and component supplier to the commercial roofing industry. SPRI is an official ANSI canvasser and has worked with representatives of the roofing industry to develop a number of consensus standards.
What is FMGlobal?
FMGlobal provides commercial and industrial property insurance and engineering-driven risk management solutions.
What are ICC & the IBC?
The International Code Council (ICC) is a non-profit organization that works to develop a single set of comprehensive and coordinated national model construction codes. The International Building Code (IBC) provides a consensus standard for construction codes.
How and when did all these organizations get involved in setting roofing industry standards?
Prior to 1980 there were no roofing edge standards by which manufacturers could hold themselves to. FM Global then created a system of standards and approvals to use on FM Global insured properties. The design community adopted this system because there were no other available standards at the time. In 1998 SPRI developed a series of three tests for judging the quality and durability of fascia and coping. These tests then allow for ES-1 approval. In 2002 the IBC wrote the ES-1 guidelines into their 2003 code. Many states have adopted the 2003 IBC, and the list is continually growing. Currently, SPRI and FM Approvals are working together to develop the next generation of the standard.
What is the ANSI/SPRI ES-1 standard?
It is a reference for those who design, specify or install edge materials used with low slope roofing systems. It addresses copings and horizontal roof edges. The following factors are considered when designing a roof edge
- Structural integrity of the substrate that anchors the edge (e.g. nailers)
- Wind resistance of the edge detail
- Materials specifications
What factors are used in ANSI/SPRI ES-1to determine the loads on a roof edge?
The key elements considered are:
- Wind Speed
- Building Occupancy
- Building Height
- Location of the edge device on Roof
- Building Location
Three tests prescribed in ES-1 are used to determine if a roof edge will withstand the determined load. RE-1: This tests the roof edge termination for mechanically attached and ballasted roofing systems. The RE-1 test evaluates the perimeter attachment to ensure that it meets a minimum holding power of 100 lbs./ft. The membrane is pulled at a 45° angle to the roof deck to simulate a billowing membrane. Failure is defined as any event that allows the membrane to come free of the edge termination or the termination to come free. RE-2: This is a pull-off test for metal edge flashing. It evaluates the strength of the metal edge flashing to ensure that the fascia system meets or exceeds the building’s calculated design wind pressure. A load is applied to the fascia metal, simulating wind load on the fascia. The calculation used is: force at failure X face area = blow-off resistance. The results must meet or exceed the calculated design wind pressure of the building. RE-3: This test is a pull-off test for metal wall coping. It evaluates the strength of the metal coping cap to ensure that it meets or exceeds the building’s calculated design wind pressure. A load is applied to the coping cap, simulating wind load. Simultaneous up and out forces are used. The calculations used to determine the blow-off resistance for the top, face leg and backleg are: force at failure X surface area = blow-off resistance. The results must meet or exceed the calculated design wind pressure of the building.
How does the code actually read?
The 2003 IBC, §1504.5: “Edge securement for low-slope roofs. Low-slope membrane roof systems metal edge securement, except gutters, installed in accordance with Section 1507, shall be designed in accordance with ANSI/SPRI ES-1, except the basic wind speed shall be determined from Figure 1609.” (Note: The Figure 1609 wind speed map varies from the wind speed map in ANSI/SPRI ES-1 1998 in the hurricane coastal regions as the map in Figure 1609 was updated in 2003) The ANSI/SPRI ES-1 document can be downloaded in its entirety for free from SPRI (www.spri.org/publications)
Which areas have adopted the 2003 IBC?
The majority of the United States has adopted some version of the IBC. Many states and municipalities have already or are scheduled to adopt the 2003 version of the IBC (www.iccsafe.org/government/adoption.html)
Who is involved in ES-1 testing and what products have been tested?
There are a variety of sources available for ES-1 tested products. Most companies producing pre-manufactured roof edge systems have had some or all of their standard products tested in accordance with the ES-1 standard. The NRCA has done testing – go to http://www.nrca.net/rp/technical/details/itslisting.aspx for more details.
What does this mean for me? Do you have any recommendations in light of recent developments?
It is important to frequently check your local requirements because additional states, counties and municipalities are in the process of adopting the 2003 IBC. Roofs with Edges designed and installed to meet ES-1 provide wind securement in the most vulnerable area of the roof, the edge.