Thermal Bridging Through Roof Fasteners: Why the Industry Should Take Note

Think that your roof doesn't need protection against hail? Think again.Severe hail events are increasing in geographic footprint and are no longer just in hail alley. The geographic region that experiences 1 inch or larger hailstones has expanded to be nearly two-thirds of the United States. Nearly 10 percent more U.S. properties, more than 6.8 million, were affected by hail in 2021 than in 2020. Coinciding with the increase in properties affected by a damaging hail event in 2021, there was also an increase in insurance claims, which rose to $16.5 billion from $14.2 billion in 2020.Figure 1: The estimated number of properties affected by one or more damaging hail events. Source: NOAA, graphed by VeriskAccording to data from Factory Mutual Insurance Company (FM Global), a leader in establishing best practices to protect buildings, the review of client losses between 2016-20, showed that the average wind/hail losses averaged $931,000 per event. That's a significant impact on a business, and it doesn't account for the other effects that a disruptive loss could have such as headaches from the process of repairing or replacing damaged roofs. As a result, designing the roof to withstand damage from hail events has become not only a best practice, but a necessity.Why does hail size matter?FM Approvals is a third-party testing and certification laboratory with a focus on testing products for property loss prevention using rigorous standards. FM Global, through the loss prevention data sheets, requires the use of FM Approved roof systems. FM Global estimates their clients lose about $130M each year on average from hail events in the United States. Given the increasing volume of severe hail events and the resulting property loss, damage, and financial impacts, FM Global added to the requirements in the FM Loss Prevention Data Sheet (LPDS) 1-34 Hail Damage in 2018. Loss Prevention Data Sheets provide FM's best advice for new construction and for Data Sheet 1-34, this includes new or reroofing projects on existing buildings. Data Sheet 1-34 provides guidelines to minimize the potential for hail damage to buildings and roof-mounted equipment. FM Global intends that the data sheets apply to its insured buildings; however, some designers use data sheets as design guidelines for buildings other than those insured by FM Global.FM's LPDS 1-34 identifies the hail hazard areas across the United States: Moderate Hail hazard area, Severe Hail hazard area, and Very Severe Hail (VSH) hazard area which are defined by hail size. Note that the VSH area roughly correlates to Hail Alley. Hail Alley receives more hailstorms, and more severe ones, compared to other parts of the country.Figure 2: FM's LPDS 1-34 map outlining the different hail categories: moderate, severe, and very severe. The Very Severe area is most commonly referred to as "Hail alley".The hail hazard areas are divided by hail size, with the Very Severe hail hazard area being the largest hail size of greater than 2 inches. As a result, roofing assemblies have to meet the most stringent hail testing for designation in the Very Severe hazard area.Figure 3: Description of FM Approval hail regions.Even if you are not in hail alley, or one of the states in FM's Very Severe Hail area, hail larger than 2 inches still has the potential to occur throughout the contiguous United States. The National Oceanic and Atmospheric Administration (NOAA) tracks weather events throughout the United States, including hail. NOAA's hail database includes information such as location, date, and magnitude (size) of the hail stone for each event. A sampling of typical data is provided below; note that several states that are outside of FM's VSH zone, had hail events that would qualify as VSH, where hail stones were recorded to be larger than 2-inches in size.Figure 4: Hail events in states that are outside of the VSH area, but qualify as VSH by size.How Do I Design For Very Severe Hail?In order for a roof assembly to achieve a hail rating, the assembly must pass a hail test. FM Approvals designs the hail tests including a different test for each hail hazard area. Hail testing generally includes the use of steel or ice balls that are dropped or launched at roof assemblies in a laboratory setting. Pass criteria vary by the test, but generally visual damage cannot be present to either the membrane or components below. Roof assemblies that pass each individual hail test are FM approved to be installed in each hail hazard area.There are thousands of FM rated assemblies and it can be difficult to choose just one. To start, it is important to note that selection consists of an entire assembly, however consideration of all roof components including the membrane, coverboard, and attachment method each play an important role in how the assembly defends against hail.Membrane selection is critical for Very Severe Hail prone regions. Thicker roof membranes, as well as higher performance grades that will remain pliable under heat and UV exposure over time and will outperform standard grade materials. Fleeceback membranes also provide an added cushion layer that buffers hail impact.Coverboard selection is a critical component of the roof system design. High compressive strength coverboards are an effective means to enhance the performance of the roof system when exposed to hail events. A coverboard will enhance the roof's long term performance by fortifying the membrane when hail strikes as well as providing a firm surface to help resist damage from typical foot traffic. It will also help the roof insulation below withstand damage from hail. While conventional gypsum coverboards and high-density polyiso coverboards provide excellent protection against foot traffic and smaller hail, they are not effective for VSH. Coverboards for VSH systems were originally limited to plywood or oriented strand board (OSB). The use of plywood and OSB is very labor intensive to install as compared to traditional gypsum coverboards, increasing the cost of the installation. Recently, coverboard manufacturers have developed glass mat roof boards which are a reinforced gypsum core with a heavy-duty coated glass mat facer. Not only do these boards provide protection against 2-inch hail and are an important part of VSH assemblies, they are also a FM Class 1 and UL Class A thermal barrier for fire rated assemblies. These boards are 5/8" thick and are 92-96 pounds per 4'x8' board; about 30 percent heavier compared to plywood yet easier to install as they can be scored and cut like a traditional gypsum board.Consideration of roof attachment method is critical for selection of VSH assemblies. Historically, mechanically attached systems were not able to pass the VSH tests; when an ice ball hit the head of the fastener or plate, the result was a laceration in the membrane. To avoid failures of the membrane at the fasteners and plates, the fasteners were traditionally buried in the system; the insulation was mechanically attached and the coverboard and membrane were adhered. This is still a common installation method and as a result, there are a large number of assemblies where the membrane and coverboard are adhered. Additionally, burying the fasteners allows for the installation of a smooth backed membrane. With the development of glass mat coverboards, there are VSH rated assemblies that can be simultaneously fastened (mechanically attached coverboard and insulation) that utilize an adhered fleece-back membrane.Figure 5: VSH systems. Left is simultaneously fastened 60 mil Fleeceback TPO over glass mat VSH roof board and Polyiso Insulation. Right is 60 mil Fleeceback TPO over glass mat VSH roof board adhered in low rise foam ribbons to mechanically attached Polyiso Insulation.Figure 6: A sample of available VSH assemblies.SummaryWhy Should We Design for VSH?Severe hail events are increasing in geographic footprint and storms with hailstones that meet Very Severe Hail criteria are occurring throughout the country. While designing for VSH is a requirement if a building falls within the VSH area and is ensured by FM Global, many owners and designers are opting for roof assemblies that can withstand VSH storms even if they are not insured by FM Global. Material selection, such as coverboard and membrane, are key components to managing this risk. Glass mat coverboards and thicker, higher grade single-ply membranes, such as fleece-back, increase the roof assembly's resistance to damage. Choosing the right roof assembly could be the difference between weathering the storm or significant damage from hail.What are the next steps?Learn about GAF's Hail Storm System Resources, and as always, feel free to reach out to the Building & Roofing Science team with questions.

Architects strive to achieve a roof design that will perform well and meet project-specific requirements. That often means incorporating the building code and warranty/guarantee requirements that building owners must meet — among the most important factors of any construction project — into the design. This isn't made any easier by the sheer number of roofing systems available. Even experienced architects can find it challenging to get familiar with all available components and identify which materials are going to be suitable for a particular building.Enter the GAF Design Services Team. Formed by merging together three different departments — field services, technical support services, and architectural information services — these technical professionals help support architects in delivering high-performing roofing systems that meet project-specific requirements.Support from Start to FinishAs GAF Senior Design Services Specialist Jesse Caruso explains, "The goal of Design Services is to essentially combine all three of those tasks into one large service team that assists architects, engineers, specifiers, consultants, sales reps, and contractors achieve their roof design goals. From the moment someone says they need a new roof, we are there throughout the entire process to provide support, all the way until the end of that roof guarantee."Each region of the country has dedicated Design Services personnel just a phone call away, ready to provide information about GAF commercial roofing systems. They understand the unique needs of different geographic areas of the country."We help walk a contractor or an owner or architect through that entire roofing lifecycle," says Caruso. "From how to install the system to what kind of warranty or guarantee you're going to get and how to maintain that guarantee or warranty."GAF's Port Arthur, TX Design Services Team: Dacia Belt, Nathan Vidrine, Shelby Noland, Brittany Castillo, Stephanie Lawrence, Melissa Vaughan, Traci Hicks, Jessica Crabtree, Traci Smith, Melanie Miller, Shelly Benoit, & Brittany SanchezSome of the topics Caruso's team is asked to assist with most frequently include:Product Testing: The Design Services team can confirm and provide documentation that shows which products and systems meet ASTM or UL standards for fire and hail resistance. They can also verify wind uplift ratings and other special approvals, such as Factory Mutual and Miami-Dade approvals.Installation Guidelines: The team can provide data on how different methods of installation can affect roofs' performance and guarantees. For instance, if a building is in a coastal area and needs a higher wind uplift rating, the team can provide guidance on fastening patterns and other installation strategies that will help meet that wind uplift requirement.Guarantee Terms: One of the most important aspects for building owners to consider is the warranty or guarantee protection provided by the roofing manufacturer. The Design Services team can assist by verifying what types of coverage are available and what contractor certifications are necessary to deliver a certain type of warranty or guarantee.Documentation: The team can provide professional documentation that supports product testing, ratings, and warranty/guarantee information. One submittal package may contain design lines, cut specs, system letters, data sheets, and more. This documentation can provide assurance from the manufacturer that the roof system will meet or exceed project requirements.An Architect's Partner for SuccessNo matter what challenges professionals may encounter while designing a new roofing system, the GAF Design Services Team is there to assist. You can be confident that the finished roofing system will provide the desired performance and protect the building for years to come.Reach out to the team by emailing designservices@gaf.com or visiting the design professionals help page.

Several changes have been included in the 2022 version of ASCE 7 as they relate to the roof. You may be thinking, 'as soon as I mastered ASCE 7-16, an updated version is set to be released!'. As with any Standard, it can be expected that updates will be made to include current research or trends. While the inclusion of tornado loads and the resulting changes in the load combinations may be the most significant, there are other updates that affect roofing as well. From minor updates to basic wind speed maps, to stepped roofs, and pavers, we have compiled a summary to help you navigate the updates. Not to fret, the changes are likely to not be incorporated until the 2024 version of IBC. However, that does not preclude incorporating these changes on current and upcoming projects.Why are these Changes Significant?The goal of the calculations in ASCE 7 are to determine the uplift pressures on a roof given project constraints including building height, location, and Risk Category. The resulting uplift pressures are then compared with tested roof assemblies to determine which assembly(ies) can be installed on a roof for each unique building. The assembly selection will also dictate the fastening method, whether it be mechanically fastened or adhered, and also the number and spacing of selected attachments. Changes in the Code may affect calculated uplift pressures that may influence the available roof assemblies.What is the Update? Updated Basic Wind Speed MapsWind speeds vary rapidly and are continuously being recorded at various locations around the world. Wind speeds are recorded in miles per hour (mph) in 3-second intervals and are collected over the course of a year. Then, the maximum values of the 3-second intervals are recorded and tracked to see the occurrence throughout the year. Since wind is a random phenomenon and the speeds vary not only by day, but also by year, the maximum 3-second intervals for each year are compared over several years. Rather than simply taking an average of wind speeds over time, the average wind speeds are analyzed by determining the Mean Recurrence Interval (MRI), which is how frequently a wind speed is equaled or exceeded during any given period of time (in years). Generally, higher wind speeds have a lower recurrence interval over time, and lower wind speeds have a higher recurrence rate over time. Analyzing this data is how wind speeds for a particular location are established.Wind speed (mph) has to be translated into units of force (psf) for design purposes in accordance with ASCE-7. The resulting forces are different in various roof zones.ASCE 7-16 has published basic wind speed contour maps for each Risk Category. The wind speed maps have contour lines that show the wind speeds throughout the United States as they vary by geographical location. It is allowable to interpolate between the contour lines, or the larger value listed on the contour line may be used. Additionally, if a location-specific wind speed is desired, an online Hazard Tool developed by ASCE will give an exact wind speed based on an address or GPS coordinates. The 2022 version updated wind speeds, primarily along the coastline. Wind speeds have generally either decreased by a few miles per hour or remained unchanged from ASCE 7-16, with the exception of several cities along the Gulf of Mexico coastline that have increased wind speeds due to recent hurricanes that have made landfall.Basic wind speeds from select coastal locations in hurricane prone regions at 33 ft for Exposure Category C are shown below. Wind speed data is shown for both ASCE 7-16 and ASCE 7-22 as a comparison.What is the Update? Wind directionality factor, Kd was movedThe wind directionality factor, Kd, was removed from the Velocity Pressure Coefficient and inserted into the Components and Cladding design wind pressures equation.The directionality factor (Kd) is a load reduction factor intended to take into account a reduced probability that the maximum wind speed will exactly coincide with the weakest direction of a building. According to ASCE 7, it accounts for the probability that the wind speed will come from any one direction given a location, and the maximum wind speed will occur from the direction that produces the maximum wind pressure on the building or its components. The directionality factor has constant factors to be used for Main Force Resisting Systems or Components and Cladding, but also accounts for various shapes of structures such as arched roofs, circular domes, and chimneys or tanks.In ASCE 7-16, Kd was located in the Velocity Pressure Equation (eq. 26.10-1) where velocity pressure, qh, is evaluated at the mean roof height, h. Where qh= qz .qh=0.00256KhKztKdKeV2 Which provides a velocity pressure in pounds per square foot (psf).The resulting value of qh is then multiplied by the external pressure coefficients (GCp) and then used to determine the wind pressure coefficients for each roof zone (perimeter, corner, field, etc.)p = qh [(Gcp) - (GCpi)] (lb/ft2)In ASCE 7-22, the velocity pressure, qh, is evaluated at the mean roof height, h. Where qh= qz by the following equation (eq. 26.10-1):qh=0.00256KhKztKeV2 Which provides a velocity pressure in pounds per square foot (psf).As you can see, the directionality factor, Kd, has been removed from the equation. In calculations for both the Main Wind Force Resisting System and Components and Cladding, Kd, has been inserted into the equations. However, since we are focusing on the roof, this falls within the Components and Cladding (C&C) calculations in Chapter 30. The design wind pressures of C&C elements are calculated with the following equations:For low rise buildings with h≤ 60 ft: (eq. 30.3-1)p = qh Kd[(Gcp) - (GCpi)] (lb/ft2)For low rise buildings with h＞60 ft: (eq. 30.4-1)p = q Kd[(Gcp) - qi Kd(GCpi)] (lb/ft2)What is the Update? Velocity Pressure Coefficients, Kz and Kh updatedThe Velocity Pressure Coefficients, Kz and Kh, for Exposures B and C were updated. Kz is the velocity pressure coefficient evaluated at height z, and Kh is the velocity pressure coefficient evaluated at height z = h. The velocity pressure at mean roof height h uses Kz. The variables are inserted into equation 26.10 to determine Velocity Pressure, qz (see equations above).What is the Update? Simplified Methods for Calculating C&C RemovedThe two simplified methods, Part 2 and Part 4 were removed from Chapter 30, Wind Loads, Components and Cladding.In the 2016 version there were two simplified methods that allowed for reduced calculations:Part 1 included calculations for Low-Rise BuildingsPart 2 was for Low-Rise Building (simplified)Part 3 included calculations for buildings with h> 60ftPart 4 was for buildings 60 ft<>Part 5 is Open BuildingsPart 6 included Building Appurtenances, Rooftop Structures, and Equipment.The 2022 version has removed the two simplified methods:Part 1 for Low-Rise BuildingsPart 2 is for buildings with h> 60ftPart 3 is Open BuildingsPart 4 includes Building Appurtenances, Rooftop Structures, and Equipment.What is the Update? Section 30.12 was added to address roof paversRoof pavers are used in IRMA (Inverted Roof Membrane Assembly) and PMRA (Protected Membrane Roof Assembly) assemblies where the roofing components are installed at the structural roof deck level and then the pavers are installed as ballast on top of the roof assembly. Roof pavers vary in size, thickness, material, and spacing, in addition to installation method and pedestal size. Pavers are considered air permeable since the gaps between pavers and the space beneath the pedestals allow for partial air pressure equalization between the surfaces. Roof pavers were only addressed in the Commentary Section C30.1 of the 2016 version and are referred to as Air Permeable Cladding. However, siding, pressure equalized rain screen walls, shingles, tiles, and aggregate roof surfacing were all included in this category. In ASCE 7-16, 'because of partial air-pressure equalization provided by air-permeable claddings, the C&C pressures services from Chapter 30 can overestimate the load on cladding elements. The designer may elect to use the loads derived from Chapter 30 or those derived by an alternate method.' While equations and methods are not included in this edition, several references are included where calculation methods may be found.In the commentary of ASCE 7-22, air permeable cladding is still defined as roof or wall claddings that allow partial air pressure equalization between the exterior and interior surfaces, with the same listing of claddings to include siding, roof pavers, and vegetative modular trays. The designer may elect to calculate the net uplift pressures of the pavers with recognized literature as noted in ASCE 7016 or Section 30.12. Section 30.12 was added to include Roof Pavers for Buildings of all heights with roof slopes less than or equal to 7 degrees. The Section includes an equation (eq. 30.12-1) to calculate design net uplift pressures:p = qhKdCLnet (lb/ft2)What is the Update? Roof Zones were revised for Hip and Gable RoofsAs wind blows over roof surfaces, it creates suction, or uplift, on the roof assemblies. The amount of uplift varies by building height, location (associated wind speed), and other factors unique to each building. The uplift created on the building is not uniformly distributed, and will vary depending on factors such as roof shape. Wind uplift is highest at the corners, then perimeters, and is the least in the field, or center of the roof; these varying wind uplift locations are called roof zones.Hip Roofs are where all four sides of the roof slopes down to connect to the exterior walls at the eaves. Gable roofs have two slanted sides that form a ridge that connect to the vertical walls that extend to the ridge. Chapter 30 of both ASCE 7-16 and 7-22 include roof zone diagrams and graphics that can be used to determine the External Pressure Coefficients (GCp).Image 1: Hip roof Image 2: Gable roofImages 1 and 2: Hip roof and gable roof, images courtesy of roofingcalc.comIn ASCE 7-22, both the roof zone diagrams and the graphics to determine GCp are updated. The roof zones are simplified to have three zones, Zone 1, Zone 2, and Zone 3 (in lieu of Zone 1, Zone 2r, Zone 2e, and Zone 3), and the accompanying zone layout was modified to include the Zone changes. The External Pressure Coefficients are determined using graphics, and those also have been updated and simplified.Components and Cladding, h ≤ 60 ft, Gable Roofs Roof Slopes 7°≤Θ≤ 20° and 20°≤Θ≤ 27°Components and Cladding, h ≤ 60 ft, Gable Roofs Roof Slopes 27°≤Θ≤ 45°Hip roofs have one roof zone layout plan for all roof slopes, however, External pressure Coefficients graphs were updated for each.What is the Update? Roof Zones were revised for Stepped RoofsStepped roofs are where buildings have multiple flat roof levels, which are often seen on large hospitals, offices, and school buildings. While stepped roofs have wind uplift pressures and corresponding roof zones, it is important to note that wind on the lower roof is affected by the neighboring higher roof sections. At the intersection of the higher roof section with the lower roof section, the wind uplift pressures are lower.New diagrams have been inserted into Chapter 30 of the ASCE 7-22 version. The primary change to note is that the corner zones, zone 3, have been changed from square shapes to L shapes. This is a reflection of the standard roof zones which have been updated from square corners to L shaped corners in more recent versions of ASCE as well.ASCE 7-16, Figure 30.3-3 Components and Cladding, h ≤ 60 ftASCE 7-22, Figure 30.3-3 Components and Cladding, h ≤ 60 ftWhat are the next steps?It is anticipated that ASCE 7-22 will be adopted in the 2024 version of the IBC, so there is plenty of time to get comfortable with the updates. And as always, feel free to reach out to the Building & Roofing Science team at buildingscience@gaf.com with questions.