What Is a Built Up Roof?

With the growing popularity and versatility of PVC roofing systems, GAF has responded by building a team of PVC experts to aid architects, specifiers, and the design community in project success. These highly trained and experienced professionals offer 1:1 support to help answer customers' questions and unique needs when working with PVC on roofing projects, and are here to help you!PVC, or polyvinyl chloride, is a single-ply thermoplastic roofing membrane. The material's characteristics help it thrive in particularly challenging applications. In fact, PVC roofing systems have a proven track record in the US, first introduced in the 1970s after making their debut in Germany a decade earlier.Here's a look at the benefits of PVC roofing systems as well as the guidance and support offered by the PVC experts at GAF.PVC Roofing Advantages and ApplicationsWhile several materials are available for use in roofing systems, PVC has been identified as a particularly long-lasting option. Accordingly, it's steadily grown in popularity nationwide.David Allor, senior area PVC specialist, joined the GAF team in 2022 as a PVC expert. His role was created specifically to support roof designers. Allor has an extensive background in the commercial roofing industry and extensive knowledge about PVC as a high-performance roofing solution."The industry refers to it as a very spec-driven product, and I believe what they're speaking to is a specifier's preference to work with a product that's been well established in the market and field tested," Allor shares. "It has the ability to provide protection against chemical exposure* and stand up well to challenging environments."While PVC may be a spec-driven product, it's also application-driven. Allor explains that PVC roofs may help provide protection for restaurants, food manufacturers, and packaging plants—any facility using animal fats where oils may be exhausted.* He also says that even if the building itself isn't exhausting gases, grease, or chemicals, it's important to consider the buildings and structures that surround it, as their exteriors may be subjected to exhaust that could degrade roofing systems.*Supporting the Design CommunityAs North America's largest roofing materials manufacturer, GAF has equipped teams with the resources and specialists needed to supply customers with more than just products. In recent years, the company built a solid team of PVC specialists that cover the entire US. These specialists assist customers with PVC specifications, roof system designs, and whatever else designers need to ensure successful project outcomes.Whether your project or design firm is based in the Northeast, Southeast, Southwest, Midwest, or West Coast, a PVC specialist is positioned to help. Allor explains the team of GAF PVC specialists is active in the organizations specifiers belong to, including the American Institute of Architects, the Construction Specifications Institute, and the International Institute of Building Enclosure Consultants.Allor describes the team's role as supporting the customer and connecting them to other GAF project support teams that can help. For instance, he said he called on a leading architectural design firm in the Boston area—and two months later, someone reached out for assistance with a specific project needing a tight turnaround."Literally within 12 hours of them reaching out to us, we replied and committed to three pertinent deliverables, those being a Tapered ISO Design Package, an Assembly Letter confirming all FM Requirements, and last but not least, a conference call the next day with the Building and Roofing Science team to go over three critical transitional details." Allor says.Committing to Successful Project OutcomesThe PVC specialists at GAF are focused on one goal: helping architects, specifiers, and the roofing design community achieve successful project outcomes through a high-performing PVC roofing system. With professionals like Allor providing insight and guidance, you can rest assured your PVC project will be in good hands.Ready to get started on your next PVC roofing project? Explore the different PVC roofing solutions available, and visit this page to find your local PVC roofing specialist who is ready to assist you.*GAF warranties and guarantees do not provide coverage against exposure to chemicals, grease, oils, animal fats or exhaust. Refer to gaf.com for more information on warranty and guarantee coverage and restrictions.

Commercial roof maintenance programs are a great way to expand your business and build long-term relationships with school facility managers. You may already be offering commercial roof maintenance services, or perhaps you're interested in branching out. Providing roof maintenance to K-12 schools and universities can be a good source of reliable, ongoing work. But you'll need to consider these facilities' nuances.Schools' Current Roof Maintenance ChallengesIn an educational environment, students' safety and comfort come first. Buildings must be secure and functional, and they must provide an atmosphere conducive to learning. Creating this environment starts with the roof, but this can easily be put off or forgotten about as many school facility managers focus on day-to-day maintenance issues. If students and teachers complain about a lack of hot water or classroom temperatures that are too hot or cold, facility managers swiftly address these issues.However, facility managers should prioritize regular roof maintenance in addition to addressing the most immediate facility concerns. Even something like a small leak from deferred roof maintenance can lead to much larger, and more costly repairs, creating headaches for everyone involved, that could have been avoided.The Value of Commercial Roof Maintenance ProgramsThe roof protects everything inside the school—from books and computers to shop equipment and musical instruments. If a roof leaks, many items could suffer damage. At the end of the day, ensuring a quality roof through regular maintenance not only protects everything inside the building, it can also help extend the life of the roof. Moreover, some roofing system manufacturers may require regular roof inspections to maintain warranties or guarantees. A roof maintenance program can meet this requirement, providing inspection records and evidence that any issues were addressed.How to Develop a Maintenance Program for SchoolsA commercial roof maintenance program for schools isn't much different from what you already do for other commercial buildings. And while regular maintenance inspections can be completed anytime, a neglected roof can often end up requiring repairs that need to align with the school's calendar to plan for minimal disruptions to the students. This can cause inconvenient delays, or date changes that could be avoided with regular inspections and maintenance.GAF Senior Product Manager Benjamin Runyan says that it's important to identify the manufacturer of the existing roofing system to ensure you are using compatible products that won't void the warranty or guarantee. "You want to be looking at this from a maintenance standpoint," says Runyan. "What does the roof look like? How was it built? How have they been maintaining it?"To start, Runyan recommends that you inspect the entire roof system and document its condition with photos and notes. Pay particular attention to the more vulnerable areas, such as seams, fasteners, flashings, edge metal, drains, and gutters. Look for cracks, missing roofing materials, evidence of ponding water, or of birds or other animals, and signs of moss or algae. An infrared scan of the roof can determine if any moisture is present and help pinpoint areas that need immediate attention.Your program should include basic tasks such as clearing debris from drains and gutters, removing leaves or branches, and making minor repairs where existing sealants are losing pliability or are showing signs of deterioration. If you identify larger concerns, you can document that with photos and provide an estimate for the repairs. Also, note how long the repairs should take and what products you'll use.Getting Started with SchoolsPreventative maintenance programs aren't just a benefit to the schools, they can also lead to other school roofing work including re-roofing opportunities. If you're ready to add school commercial maintenance programs to your business plan, GAF has the resources you need to get started. Runyan explains, "Your first step should be talking with your GAF Territory Manager as they will likely already have established relationships with school districts, colleges, roof consultants and architects in your service area."From commercial roofing system specifications to WellRoof® Guarantee Extensions, plus roof restoration options, GAF meets all your needs for stepping into the world of educational buildings.

What is going on here?No, this roof does not have measles, it has a problem with thermal bridging through the roof fasteners holding its components in place, and this problem is not one to be ignored.As building construction evolves, you'd think these tiny breaches through the insulating layers of the assembly, known as point thermal bridges, would matter less and less. But, as it happens, the reverse is true! The tighter and better-insulated a building, the bigger the difference all of the weak points, in its thermal enclosure, make. A range of codes and standards are beginning to address this problem, though it's important to note that there is often a time lag between development of codes and their widespread adoption.What Is the Industry Doing About It?Long in the business of supporting high-performance building enclosures, Phius (Passive House Institute US) provides a Fastener Correction Calculator along with a way to calculate the effect of linear thermal bridges (think shelf angles, lintels, and so on). By contrast, the 2021 International Energy Conservation Code also addresses thermal bridging, but only considers framing materials to be thermal bridges, and actually pointedly ignores the effects of point loads like fasteners in its definition of continuous insulation: "insulation material that is continuous across all structural members without thermal bridges other than fasteners and service openings" (Section C202). Likewise, The National Energy Code of Canada for Buildings: 2020 addresses thermal bridging of a number of building components, but also explicitly excludes fasteners: "in calculating the overall thermal transmittance of assemblies…fasteners need not be taken into account" (Section 3.1.1.7.3). Admittedly, point thermal bridges are often excluded because it is challenging to assess them with simple simulation tools.Despite this, researchers have had a hunch for decades that thermal bridging through the multitude of fasteners often used in roofs is in fact significant enough to warrant study. Investigators at the National Bureau of Standards, Oak Ridge National Laboratory, the National Research Council Canada, and consulting firms Morrison Hershfield and Simpson Gumpertz & Heger (SGH), have conducted laboratory and computer simulation studies to analyze the effects of point thermal bridges.Why Pay Attention Now?The problem has been made worse in recent years because changes in wind speeds, design wind pressures, and roof zones as dictated by ASCE 7-16 and 7-22 (see blogs by Jim Kirby and Kristin Westover for more insight), mean that fastener patterns are becoming denser in many cases. This means that there is more metal on average, per square foot of roof, than ever before. More metal means that more heat escapes the building in winter and enters the building in summer. By making our buildings more robust against wind uplift to meet updated standards, we are in effect making them less robust against the negative effects of hot and cold weather conditions.So, how bad is this problem, and what's a roof designer to do about it? A team of researchers at SGH, Virginia Tech, and GAF set out to determine the answer, first by simplifying the problem. Our plan was to develop computer simulations to accurately anticipate the thermal bridging effects of fasteners based on their characteristics and the characteristics of the roof assemblies in which they are used. In other words, we broke the problem down into parts, so we could know how each part affects the problem as a whole. We also wanted to carefully check the assumptions underlying our computer simulation and ensure that our results matched up with what we were finding in the lab. The full paper describing our work was delivered at the 2023 IIBEC Convention and Trade Show, but here are the high points, starting with how we set up the study.First, we began with a simple 4" polyisocyanurate board (ISO), and called it Case A-I.Next, we added a high-density polyisocyanurate cover board (HD ISO), and called that Case A-II.Third, we added galvanized steel deck to the 4" polyiso, and called that Case A-III.Finally, we created the whole sandwich: HD ISO and ISO over steel deck, which was Case A-IV.Note that we did not include a roof membrane, substrate board, air barrier, or vapor retarder in these assemblies, partly to keep it simple, and partly because these components don't typically add much insulation value to a roof assembly.The cases can be considered base cases, as they do not yet contain a fastener. We needed to simulate and physically test these, so we could understand the effect that fasteners have when added to them.We also ran a set of samples, B-I through B-IV, that corresponded with cases A-I through A-IV above, but had one #12 fastener, 6" long, in the center of the 2' x 2' assembly, with a 3" diameter insulation plate. These are depicted below. The fastener penetrated the ISO and steel deck, but not the HD ISO.One visualization of the computer simulation is shown here, for Case B-IV. The stripes of color, or isotherms, show the vulnerability of the assembly at the location of the fastener.What did we find? The results might surprise you.First, it's no surprise that the fastener reduced the R-value of the 2' x 2' sample of ISO alone by 4.2% in the physical sample, and 3.4% in the computer simulation (Case B-I compared to Case A-I).When the HD ISO was added (Cases II), R-value fell by 2.2% and 2.7% for the physical experiment and computer simulation, respectively, when the fastener was added. In other words, adding the fastener still caused a drop in R-value, but that drop was considerably less than when no cover board was used. This proved what we suspected, that the HD ISO had an important protective effect against the thermal bridging caused by the fastener.Next, we found that the steel deck made a big difference as well. In the physical experiment, the air contained in the flutes of the steel deck added to the R-value of the assembly, while the computer simulation did not account for this effect. That's an item that needs to be addressed in the next phase of research. Despite this anomaly, both approaches showed the same thing: steel deck acts like a radiator, exacerbating the effect of the fastener. In the assemblies with just ISO and steel deck (Cases III), adding a fastener resulted in an R-value drop of 11.0% for the physical experiment and 4.6% for the computer simulation compared to the assembly with no fastener.Finally, the assemblies with all the components (HD ISO, ISO and steel deck, a.k.a. Cases IV) showed again that the HD ISO insulated the fastener and reduced its negative impact on the R-value of the overall assembly. The physical experiment had a 6.1% drop (down from 11% with no cover board!) and the computer simulation a 4.2% drop (down from 4.6% with no cover board) in R-value when the fastener was added.What Does This Study Tell Us?The morals of the study just described are these:Roof fasteners have a measurable impact on the R-value of roof insulation.High-density polyisocyanurate cover boards go a long way toward minimizing the thermal impacts of roof fasteners.Steel deck, due to its high conductivity, acts as a radiator, amplifying the thermal bridging effect of fasteners.What Should We Do About It?As for figuring out what to do about it, this study and others first need to be extended to the real world, and that means making assumptions about parameters like the siting of the building, the roof fastener densities required, and the roof assembly type.Several groups have made this leap from looking at point thermal bridges to what they mean for a roof's overall performance. The following example was explored in a paper by Taylor, Willits, Hartwig and Kirby, presented at the RCI, Inc. Building Envelope Technology Symposium in 2018. In that paper, the authors extended computer simulation results from a 2015 paper by Olson, Saldanha, and Hsu to a set of actual roofing scenarios. They found that the installation method has a big impact on the in-service R-value of the roof.They assumed a 15,000-square-foot roof, fastener patterns and densities based on a wind uplift requirement of 120 pounds per square foot, and a design R-value of R-30. In this example, a traditional mechanically attached roof had an in-service R-value of only R-25, which is a 17% loss compared to the design R-value.An induction-welded roof was a slight improvement over the mechanically attached assembly, with an in-service value of only R-26.5 (a 12% loss compared to the design R-value).Adhering instead of fastening the top layer of polyiso resulted in an in-service R-value of R-28.7 (a 4% loss compared to the design R-value).Finally, in their study, an HD polyiso board was used as a mechanically fastened substrate board on top of the steel deck, allowing both layers of continuous polyiso insulation and the roof membrane to be adhered. Doing so resulted in an in-service R-value of R-29.5, representing only a 1.5% loss compared to the design R-value.To operationalize these findings in your own roofing design projects, consider the following approaches:Consider eliminating roof fasteners altogether, or burying them beneath one or more layers of insulation. Multiple studies have shown that placing fastener heads and plates beneath a cover board, or, better yet, beneath one or two layers of staggered insulation, such as GAF's EnergyGuard™ Polyiso Insulation, can dampen the thermal bridging effects of fasteners. Adhering all or some of the layers of a roof assembly minimizes unwanted thermal outcomes.Consider using an insulating cover board, such as GAF's EnergyGuard™ HD or EnergyGuard™ HD Plus Polyiso cover board. Installing an adhered cover board in general is good roofing practice for a host of reasons: they provide enhanced longevity and system performance by protecting roof membranes and insulation from hail damage; they allow for enhanced wind uplift and improved aesthetics; and they offer additional R-value and mitigate thermal bridging as shown in our recent study.Consider using an induction-welded system that minimizes the number of total roof fasteners by dictating an even spacing of insulation fasteners. The special plates of these fasteners are then welded to the underside of the roof membrane using an induction heat tool. This process eliminates the need for additional membrane fasteners.Consider beefing up the R-value of the roof insulation. If fasteners diminish the actual thermal performance of roof insulation, building owners are not getting the benefit of the design R-value. Extra insulation beyond the code minimum can be specified to make up the difference.Where Do We Go From Here?Some work remains to be done before we have a computer simulation that more closely aligns with physical experiments on identical assemblies. But, the two methods in our recent study aligned within a range of 0.8 to 6.7%, which indicates that we are making progress. With ever-better modeling methods, designers should soon be able to predict the impact of fasteners rather than ignoring it and hoping for the best.Once we, as a roofing industry, have these detailed computer simulation tools in place, we can include the findings from these tools in codes and standards. These can be used by those who don't have the time or resources to model roof assemblies using a lab or sophisticated modeling software. With easy-to-use resources quantifying thermal bridging through roof fasteners, roof designers will no longer be putting building owners at risk of wasting energy, or, even worse, of experiencing condensation problems due to under-insulated roof assemblies. Designers will have a much better picture of exactly what the building owner is getting when they specify a roof that includes fasteners, and which of the measures detailed above they might take into consideration to avoid any negative consequences.This research discussed in this blog was conducted with a grant from the RCI-IIBEC Foundation and was presented at IIBEC's 2023 Annual Trade Show and Convention in Houston on March 6. Contact IIBEC at https://iibec.org/ or GAF at BuildingScience@GAF.com for more information.