Skylight Design Lets Glass Take the Spotlight

Good skylight design and project integration can mean a product not only provides light and possible ventilation — it also can make a statement as a strong aesthetic component.
Photo: Wasco

Skylights continue to gain recognition as energy-efficient daylight harvesting devices. When properly specified, proportioned, located and installed, skylights can meet the latest editions of national model energy conservation and green building codes and rating systems. Beyond the concerns of daylighting and thermal performance, skylights also must serve as a viable element of the building envelope.

Consequently, given the growing use of large, complex sloped glazing systems, design criteria for skylights and sloped glazing  are undergoing rapid creative evolution, as are the codes — primarily the International Building Code (IBC) — governing their application. In some cases, best practice can be to consider requirements in excess of those in the codes. Sloped glazing is defined in building codes as those where glass is inclined 15 degrees or more from vertical.

Potential Breakage is Key

Proper glass selection and system design is intended to meet specified design load(s), with the primary goal of reducing the probability of glass breakage, which can pose risks to people and property.

Breakage may occur due to several factors, either alone or in combination, some of which are noted below:

  • Loads in excess of the specified design loads
  • Large thermal stresses
  • Damage to the glass during handling or installation
  • Forces exerted by the framing system
  • Vandalism
  • Wind-borne gravel or other debris
  • Large hailstones
  • Impurities in the glass causing spontaneous fracture
Proper glass selection and system design must meet specified design load(s), with the primary goal of reducing the probability of glass breakage, which can pose risks to people and property. Photo: CrystaLite

The differences in design considerations between vertical and sloped glazing must be considered. For example, sloped glass is more susceptible to impact from falling objects than vertical glass. Sloped glazing is also more likely to fall from its opening when it breaks than vertical glass.

Typically, the preferred practice for glass selection in skylights and sloped glazing is to provide firm support for all edges of the glass for both inward (positive) and outward (negative) loads. This is mandatory for insulating glass units. The support may be by conventional channel glazing or by structural retention with a silicone sealant.

Design Considerations

Glazed systems require special glass design considerations. Designers and architects must orchestrate the use of such industry and regulatory standards and guidelines, as ASTM E1300-16,Standard Practice for Determining Load Resistance of Glass in Buildings,” ASCE/SEI 7,Minimum Design Loads for Buildings and Other Structures,” and others, as well as the IBC and International Residential Code (IRC).

Glazed systems of skylights often require special glass design considerations when designing for things like structure, thermal design and control of solar heat gain. Designers and architects must orchestrate the use of industry and regulatory standards and guidelines. Photos: FGIA

Once the 2021 edition of the IBC is adopted, new code language in IBC Section 2405.1, 2405.3 will clarify that screens are not required below skylights and sloped glazing when 30-mil interlayer laminated glass is used. The use of 30 mil-laminated glass in skylights improves daylighting, aesthetics, and helps protect building occupants, along with eliminating the need for screens.

Other design considerations are outlined below.

Strength

At base, the selection of glass for skylights and sloped glazing begins with the use of ASTM E1300, which uses a failure prediction model with the glass strength based on weathered glass. This takes into account a rational reduction in glass strength from initial production to in-service use. The procedure determines if the proposed glass type (annealed, heat-strengthened, fully tempered or laminated) will meet the specified load, allowing it to be determined whether to consider either a thinner or thicker glass.

A skylight is an integral part of the building envelope, controlling the movement of moisture and air. Photos: FGIA

ASTM E1300 supplies load resistance charts for a glass probability of breakage of eight per 1000, as this is considered practical and reasonable for most glass applications. The designer should aim for a low probability of breakage, but if breakage does occur, the consequences must be acceptable.

ASCE/SEI 7 lists formulas for calculating the equivalent combined pressure due to a combination of dead, wind, snow and other loads, as does Chapter 24 of the IBC. For common shapes of buildings, background guidance on design wind velocities may be found in ASCE/SEI 7 — with a caveat: buildings of unusual shape or geometry may render that standard inadequate for defining loads on sloped glazing and skylights.

Load Duration

The strength of glass is a function of load duration. Long duration loads, or any load lasting approximately 30 days, such as snow loads, must be treated differently than short duration loads, defined as any load lasting three seconds or less, such as wind loads.

Surface Damage

Mechanical damage to the surface of glass, as opposed to weathering, can cause a significant reduction in glass strength.

Thermal stress happens where there is a mix of heavy sunlight and shade. Glass must accommodate these changes. Photo: CrystaLite

Flat glass surfaces inherently have numerous, randomly occurring, microscopic flaws, resulting in widely varying strengths among otherwise identical lites. (A lite is a pane of glass or an insulating glass unit used in a window, door, tubular daylighting device, roof window, secondary storm product or unit skylight.)

So, the strength of glass exposed to transient and static loads must be analyzed on a statistical basis. This may be expressed in various ways, one of which is the coefficient of variation, a measure of the distribution of the glass strength for a large number of lites. It is influenced by the degree of heat treatment of the glass, being highest (0.25) for annealed and lowest for fully tempered glass (0.10) due to surface compression of the latter. This minimizes the tendency of surface flaws to propagate under load and cause glass breakage.

Impact From Wind-Borne Items

Limiting deflection of the frame is important. Care should be taken not to bow or distort the frame due to over-compaction of insulation. Photos: FGIA

The ability of fenestration of all types to resist such impacts is especially important in areas where high wind events, such as hurricanes, regularly occur. Building codes or other regulations in these areas frequently require that fenestration products either be rated as impact-resistant or be protected by impact-resistant devices. Resistance to hail impact — especially applicable to skylights — is a special case of impact resistance. Here, FM 4431, “Approval Standard for Skylights,” is often the governing standard.

Thermal Stress

Differential thermal expansion between framing and glazing, as well as between exposed and shaded areas of a given lite, must be accommodated through appropriate glass bite dimensions and selection of proper sealant, as well as glass type. For most orientations, the temperature that sloped glass may reach is usually higher than for vertical glazing due to the sun’s radiation being oriented more directly to the glass surface. Consequently, thermal stresses created in the glass most often require heat treated glass (heat-strengthened or fully tempered).

Edge Strength

Both the design of the skylight system and the integration into the structure of the building take careful consideration to ensure water is controlled and drained away properly. It is imperative in all glazing systems that water infiltration and condensation be drained or weeped away from edges of the glass and away from the skylight system.

The quality of the glass cutting and the edge finish are critical variables. For example, good quality, clean cut glass edges have an average strength of about 4650 psi (32 MPa) and a predicted failure of 1 percent at about 2,400 psi (16 MPa). For very poorly cut, nipped or damaged edges, the average strength may be in the range of 1,200-1,500 psi (8-10 MPa).

Frame Deflection Limits

A supported glass edge should have an edge deflection limited by the framing member to no greater than L/175 where “L” is the length of the glass edge and the deflection is determined by the displacement of the framing member along the edge.

Water Drainage

It is imperative in all glazing systems that water infiltration and condensation be drained or weeped away from the edges of the glass. This is to prevent detrimental freezing of the water or deleterious effects of moisture on edge seals of insulating glass, or possible debonding of interlayer material in laminated glass. The framing system must always drain the water from the lowest point of the glazing channel and the lowest point of the framing system.

All these design considerations and more, as well as guidance in applying them, are detailed in AAMA GDSG-1, Glass Design Guide for Sloped Glazing and Skylights, published by the Fenestration and Glass Industry Alliance (FGIA). Other published FGIA resources include the following.

  • AAMA SDGS-1-89, “Structural Design Guidelines for Aluminum Framed Skylights”
  • AAMA TIR-A7-11, “Sloped Glazing Guidelines”
  • AAMA TIR-A11-15, “Maximum Allowable Deflection of Framing Systems for Building Cladding Components at Design Wind Loads”
  • IGMA TB-3001, “Guidelines for Sloped Glazing”

All are available at aamanet.org/store.

About the author: Glenn Ferris is the Fenestration and Glass Industry Alliance’s (FGIA’s) Fenestration Standards Specialist. He began his career with the association in 2018. He has extensive experience in the fenestration industry dating back to 1992. Ferris is a liaison for many councils, committees and study/work/task groups guiding them in the completion of the scope of each group.

SPRI Updates and Improves Roof Edge Standards

Low-slope metal perimeter edge details, including fascia, coping and gutters, are critical systems that can strongly impact the long-term performance of single-ply roofs. Photo: Johns Manville

The effect of high winds on roofs is a complex phenomenon, and inadequate wind uplift design is a common factor in roofing failures. Damage from wind events has historically been dramatic, and wind-induced roof failure is one of the major contributors to insurance claims.

Roofing professionals have long recognized the importance of proper low-slope roof edge and gutter designs, particularly in high-wind conditions. For this reason, SPRI, the association representing sheet membrane and component suppliers to the commercial roofing industry, has spent more than a decade enhancing testing and design standards for these roofing details.

SPRI introduced the first version of its landmark standard, ANSI/SPRI/ES-1 “Wind Design Standard for Edge Systems Used with Low Slope Roofing Systems” in 1998. Since then, the association has continually revised, re-designated and re-approved the document as an ANSI (American National Standards Institute) standard.

Testing of edge securement per ANSI/SPRI ES-1 is required per the International Building Code (IBC), which has been adopted by every state in the country.

This standard provides the basic requirements for wind-load resistance design and testing for roof-edge securement, perimeter edge systems, and nailers. It also provides minimum edge system material thicknesses that lead to satisfactory flatness, and designs to minimize corrosion.

Construction professionals have been successfully using the standard, along with the specifications and requirements of roofing membrane and edge system manufacturers to strengthen their wind designs.

Until recently, the biggest news on the wind design front was the approval of ANSI/SPRI/FM 4435/ES-1, “Wind Design Standard for Edge Systems Used with Low-slope Roofing Systems.” Let’s call it “4435/ES-1” for short. SPRI knew recent post-hurricane investigations by the Roofing Industry Committee on Weather Issues (RICOWI) and investigations of losses by FM Global consistently showed that, in many cases, damage to a low-slope roof system during high-wind events begins when the edge of the assembly becomes disengaged from the building. Once this occurs, the components of the roof system (membrane, insulation, etc.) are exposed. Damage then propagates across the entire roof system by peeling of the roof membrane, insulation, or a combination of the two.

Recognizing that edge metal is a leading cause of roof failures, SPRI has redoubled its efforts to create a series of new and revised documents for ANSI approval. As has always been the case, ANSI endorsement is a critical step toward the ultimate goal of getting these design criteria included in the IBC.

A Systems Approach to Enhancing Roof Edge Design

Roofing professionals understand that successful roof design requires the proper integration of a wide variety of roofing materials and components. For years, leading roofing manufacturers have taken a “systems” approach to their product lines. Recently, SPRI has zeroed in on the roof edge. Low-slope, metal perimeter edge details include fascia, coping and gutters, are critical systems that can strongly impact the long-term performance of single-ply roofs.

As part of the ES-1 testing protocol, RE-3 tests upward and outward simultaneous pull of a horizontal and vertical flanges of a parapet coping cap. Photo: OMG Edge Systems

SPRI first addressed roof gutters in 2010 with the development of ANSI/SPRI GD-1. The testing component of this document was recently separated out to create a test standard and a design standard. The test standard, GT-1, “Test Standard for Gutter Systems,” which was approved as an American National Standard on May 25, 2016.

Similarly, SPRI has revised 4435/ES-1 to only be a test standard.

Making both edge standards (4435/ES-1 and GT-1) into standalone testing documents makes it easier for designers, contractors and building code officials to reference the testing requirements needed for metal roof edge systems.

IBC requires that perimeter edge metal fascia and coping (excluding gutters), be tested per the three test methods, referred to as RE-1, RE-2 and RE-3 in the ES-1 standard. The design elements of ES-1 were never referenced in code, which caused some confusion as to how ES-1 was to be applied. The latest version of 4435/ES-1 (2017) only includes the tests referenced in code to eliminate that confusion.

Test methods in 4435/ES-1 2017 have the same names (RE-1, RE-2, and RE-3), and use the same test method as 4435/ES-1 2011. Because there are no changes to the test methods, any edge system tested to the 2011 version would not need to be retested using the 2017 version.

FM Global’s input was instrumental in the changes in 2011 when ANSI/SPRI ES-1 incorporated components of FM 4435 to become 4435/ES-1. However, there are no additional FM related changes in the latest 4435/ES-1 standard.

This gravel stop is being tested according to the ANSI/SPRI ES-1 standard using the RE-2 test for fascia systems. Photo: OMG Edge Systems

Per ANSI requirements, 4435/ES-1 2011 needed to be re-balloted, which is required by ANSI every five years. SPRI took this opportunity to have it approved as a test standard only to eliminate the confusion referenced above. FM Global was consulted and indicated it wanted to keep “FM” in the title. (FM was on the canvas list for the test standard and actually uses it as its own test standard.)

With 4435/ES-1 becoming a test standard for coping and fascia only, and GT-1 being a test standard for gutters, SPRI determined that a separate edge design standard was needed. Meet ED-1, a design standard for metal perimeter edge systems.

The design portions of the ES-1 edge and the GD-1 gutter standards have been combined and are now referenced by SPRI as ED-1. It has been developed and is currently being canvassed as an ANSI standard that will provide guidance for designing all perimeter edge metal including fascia, coping, and gutters.

ED-1 will be canvassed per the ANSI process later this year. However, SPRI is not planning to submit ED-1 for code approval.

SPRI ED-1 will include:

Material Design

  • Nailer attachment
  • Proper coverage
  • Recommended material thicknesses
  • Galvanic compatibility
  • Thermal movement
  • Testing requirements
  • “Appliance” attachment to edge systems

Limited Wind Design

  • Load to be required by the Authorities Having Jurisdiction (AHJ).
  • Tables similar to those included in 4435/ES-1 will be included for reference.

If this sounds a tad complex, imagine the design work required by the dedicated members of SPRI’s various subcommittees.

The Test Methods in Detail

The GT-1 standard is the newest, so let’s tackle this one first. As noted above, the ANSI/SPRI GT-1 test standard was developed by SPRI and received ANSI Approval in May of 2016. Testing of roof gutters is not currently required by IBC; however, field observations of numerous gutter failures in moderate to high winds, along with investigations by RICOWI following hurricanes have shown that improperly designed or installed gutters frequently fail in high wind events. GT-1 provides a test method that can be used by manufacturers of gutters, including contractors that brake or roll-form gutters, to determine if the gutter will resist wind design loads. Installing gutters tested to resist anticipated wind forces can give contractors peace of mind, and may provide a competitive advantage when presented to the building owner.

This gutter is being tested using the test method specified in ANSI/SPRI GD-1, “Design Standard for Gutter Systems Used with Low-Slope Roofs.” Photo: OMG Edge Systems

GT-1 tests full size and length samples (maximum 12 feet 0 inches) of gutter with brackets, straps, and fasteners installed per the gutter design. It is critical that the gutter be installed with the same brackets, straps, and fasteners, at the same spacing and locations as per the tested design to assure the gutter will perform in the field as tested. The fabricator should also label the gutter and/or provide documentation that the gutter system has been tested per GT-1 to resist the design loads required.

GT-1 consists primarily of three test methods (G-1, G-2, and G-3). Test method G-1 tests the resistance to wind loads acting outwardly on the face of the gutter, and G-2 tests the resistance to wind loads acting upwardly on the bottom of the gutter. G-3 tests resistance to the loads of ice and water acting downwardly on the bottom of the gutter.

Tests G-1 and G-2 are cycled (load, relax, increase load) tests to failure in both the original GD-1 standard and the new GT-1. The only change being that in GD-1 the loads are increased in increments of 10 lbf/ft2 (pound force per square foot) from 0 to failure, and in GT-1 they are increased in increments of 15 lbs/lf (pounds per linear foot) from 0 to 60 lbs/lf, then in 5 lbs/lf increments from above 60 lbs/lf to failure.

Note also that the units changed from lbf/ft2 (pound force per square foot) to lbs/lf (pounds per linear foot), which was done so that the tests could be run using the test apparatus loads without having to convert to pressures.

The GT-1 standard specifies a laboratory method for static testing external gutters. However, testing of gutters with a circular cross-section is not addressed in the standard, nor does the standard address water removal or the water-carrying capability of the gutter. In addition, downspouts and leaders are not included in the scope of the standard.

SPRI intends to submit ANSI/SPRI GT-1 for adoption in the next IBC code cycle.

As referenced above, IBC requires that perimeter edge metal (fascia and coping), excluding gutters, be tested per three test methods, referred to as RE-1, RE-2 and RE-3 in the ES-1 standard.

RE-1 tests the ability of the edge to secure a billowing membrane, and is only required for mechanically attached or ballasted membrane roof systems when there is no peel stop (seam plate or fasteners within 12 inches of the roof edge). RE-2 tests the outward pull for the horizontal face of an edge device. RE-3 tests upward and outward simultaneous pull on the horizontal and vertical sides of a parapet coping cap.

Calculating Roof Edge Design Pressures

All versions of ANSI/SPRI ES-1 and ANSI/SPRI GD-1, the 2011 version of ANSI/SPRI 4435/ES-1, and the new ED-1 standard all provide design information for calculating roof edge design pressures. These design calculations are based on ASCE7 (2005 and earlier), and consider the wind speed, building height, building exposure (terrain), and building use.

A gravel stop failure observed during roof inspections after Hurricane Ike in Sept. 2008. Photo: OMG Edge Systems

However, as stated above, IBC requires that the load calculation be per Chapter 16 of code, so the SPRI design standards are intended only as a reference for designers, fabricators, and installers of metal roof edge systems.

ES-1-tested edge metal is currently available from pre-manufactured suppliers, membrane manufacturers and metal fabricators that have tested their products at an approved laboratory.

The roofing contractor can also shop-fabricate edge metal, as long as the final product is tested by an approved testing service. The National Roofing Contractors Association (NRCA) has performed lab testing and maintains a certification listing for specific edge metal flashings using Intertek Testing Services, N.A. Visit www. nrca.net/rp/technical/details/files/its details.pdf for further details.

A list of shop fabricators that have obtained a sub-listing from NRCA to fabricate the tested edge metal products are also available at www. nrca.net/rp/technical/details/files/its details/authfab.aspx.

SPRI Continues to Take Lead Role in Wind Testing

As far back as 1998, SPRI broke ground with its ANSI/SPRI/ES-1 document addressing design and testing of low-slope perimeter edge metal. Today, the trade association has a variety of design documents at the roofing professional’s disposal, and is working to get ED-1 approved as an Edge Design Standard to be used for low-slope metal perimeter edge components that include fascia, coping and gutters.

All current and previously approved ANSI/SPRI standards can be accessed directly by visiting https://www.spri.org/publications/policy.htm.

For more information about SPRI and its activities, visit www.spri.org or contact the association at info@spri.org.

Polymer Roofing Tiles Feature Quarried Look that Replicates Natural Slate

DaVinci Multi-Width Slate tiles come in five different widths—12-, 10-, 9-, 7- and 6-inch—and are available in a number of different color blends.

DaVinci Multi-Width Slate tiles come in five different widths—12-, 10-, 9-, 7- and 6-inch—and are available in a number of different color blends.

Following the successful introduction of a Single-Width Slate 12-inch tile with an enhanced profile in early 2015, DaVinci Roofscapes showcased the availability of the more realistic profiles on the company’s Multi-Width Slate and Bellaforté Slate polymer roofing tiles at the 2016 International Builders’ Show.

Details on the edges of the DaVinci slate tiles now have a more accurate quarried look that replicates natural slate. Deeper impressions in the tiles make them appear thicker, even though they’re the same weight as the previous tiles.

Low-maintenance slate tiles from DaVinci resist algae and moss growth, come in 50 standard colors and are rated for installation in areas experiencing high winds, hail and wildfires. DaVinci Multi-Width Slate tiles come in five different widths—12-, 10-, 9-, 7- and 6-inch—and are available in a number of different color blends. Single-Width Slate and Bellaforté Slate tiles from DaVinci are available in a 12-inch tile width, also in a variety of color blends.

Gateway Safety Receives Recognition Award from Industrial Buyers Group

Gateway Safety was awarded the President’s Club Recognition for achievement by the Industrial Buyers Group (IBC). Suppliers and distributors are recognized by IBC for their contributions during the year and rated on percentage growth.

“We annually recognize the distinguished suppliers who support the regional independent distributors who are part of the IBC marketing group,” says Rich Poole, IBC’s Industrial Division vice president. “Gateway’s support of our distributors’ sales initiatives and marketing programs earned them this distinction. We are proud to have Gateway as one of our select Preferred Suppliers, and are proud to recognize their contributions to our organization.”

Gateway Safety has been an IBC Preferred Supplier since 2010, partnering with IBC distribution members to provide safety products in eye, face, head, hearing and disposable respiratory protection. Matthew Love, Gateway Safety’s vice president, attended the meeting and accepted the award on the company’s behalf.

“We feel honored and are thankful to IBC for recognizing us with this award,” says Love. “Gateway Safety’s success within the IBC organization can be attributed to the great relationships we have formed with our IBC distribution partners. Safety equipment is a great fit for IBC distributors, since categories like eye and face protection can really complement an industrial product line,” continues Love. “Our achievement with IBC shows that safety products remain a growing market need.”

IBC is one of North America’s alliances of industrial, bearing and power transmission, electrical, and subassembly distributors with more than 550 branch locations.

AEP Span, ASC Building Products Granted IAPMO’s Uniform Evaluation Service Evaluation Report ER-0309

AEP Span and ASC Building Products have been granted IAPMO’s Uniform Evaluation Service (UES) Evaluation Report ER-0309 which demonstrates compliance to the 2012 and 2009 editions of the International Building Code (IBC) and the International Residential Code (IRC).

IAPMO’s UES program lowers the cost and increases the value to code officials of these reports by combining all of these recognitions in one concise report prepared by an internationally recognized product certification body.

The UES ER-0309 states the Single Skin Steel Roof and Wall Panels with Concealed Fasteners listed in the report satisfy the applicable code requirements which allow for the specification of AEP Span and ASC Building Products listed panels to architects, contractors, specifiers, and designers, and approval of installation by code officials. It also provides code officials with a concise summary of the products’ attributes and documentation of code compliance included in the report. The UES program is built upon IAPMO’s more than 70 years of experience in evaluating products for code compliance, and their evaluation services are ISO

Guide 65 Compliant by American National Standards Institute (ANSI) and meet the requirements of IBC/CBC Section 1703 for approval agencies.

ASC Profiles LLC is a subsidiary of BlueScope Steel and Nippon Steel & Sumitomo Metals Corporation. ASC Profiles is an industry leading manufacturer of cold-formed steel building components since 1971. ASC Profiles consists of three distinct business divisions, each serving a different market segment within the industry. ASC Steel Deck delivers a high quality line of structural roof and floor deck that has been fully tested for the commercial construction market. AEP Span provides architecturally engineered panels for steel roof and siding products for the commercial and industrial markets. ASC Building Products offers high quality steel roof and wall panels for the residential, light commercial, and agricultural markets.

Wind Loading on Rooftop Equipment

I recently attended a continuing-education conference for civil/structural engineers that discussed changes in the 2012 International Building Code (IBC) and the referenced ASCE 7-10 “Minimum Design Loads for Buildings and Other Structures”. During the seminar, the question was asked: “Who is responsible for the design of wind loading to rooftop equipment as defined in the IBC and Chapter 29 of ASCE 7-10?” The most accepted response was to add a section in the structural general notes that wind design on rooftop equipment is to be designed “by others”.

A structural engineer designed the metal support system and load transfer from the new HVAC unit down through the structure.

A structural engineer designed the metal support system and load transfer from the new
HVAC unit down through the structure.

The design requirements for wind loading on rooftop equipment have been included in previous editions of the IBC and ASCE 7, but significant changes have been included in ASCE 7-10. The increased attention is in part because of more severe wind events in recent years. While it is not the primary responsibility of the roofing consultant or contractor to evaluate the systems being placed on the roof, it is good to understand the code’s requirements for loading to rooftop equipment, how the load is determined and applied, and how the load is transferred to the building structure.

CODE REQUIREMENTS

The primary focus of the roofing professional in the IBC is concentrated on Chapter 15 (Roof Assemblies). While there are requirements in Chapter 15 addressing rooftop structures, these requirements, particularly in relation to wind loading, extend beyond Chapter 15. It is therefore imperative to be familiar with other sections of the code.

For instance, Section 1504 (Performance Requirements) refers the user multiple times to Chapter 16 (Structural Design) for wind-loading-design requirements. While roof manufacturers typically prequalify their systems based on various industry standards (ASTM, FM, ANSI, etc.), rooftop equipment supports are not typically prequalified because of the variability of placement and conditions. Similarly, new to this code cycle, Section 1509.7.1 includes the requirement for wind resistance for rooftop-mounted photovoltaic systems per Chapter 16 of the IBC. Other industries or trades have similar requirements. Section 301.15 of the 2012 International Mechanical Code and Section 301.10 of the 2012 Fuel and Gas Code require “equipment and supports that are exposed to wind shall be designed to resist the wind pressures in accordance with the IBC”.

Section 1609 of Chapter 16 (Wind Loads) applies to wind loading on every building or structure. Section 1609.1.1 provides two design options. The designer can use chapters 26 to 30 of ASCE 7-10 or Section 1609.6 of the IBC. Note however that Section 1609.6 is based on the design procedures used in Chapter 27 of ASCE 7-10, which does not address wind loading on rooftop equipment and thus is not applicable. Chapter 29 of ASCE 7-10 (Wind Loading on Other Structure and Building Appurtenances) contains the procedures used to determine wind loading on rooftop structures and equipment.

DETERMINING AND APPLYING WIND LOADING ON ROOFTOP EQUIPMENT

Properly specified ballasting blocks are designed and formed to better address the freeze/thaw cycle.

Properly specified ballasting blocks are designed and formed to better address the freeze/thaw cycle.


To determine wind loading on rooftop equipment, the first step is to identify the building Risk Category (formerly the Occupancy Category) and the building location. The Risk Category is determined from Section 1604.5 and Table 1604.5 of the IBC or Table 1.5-1 of ASCE 7-10. There are slight variations in the two codes but typically each will produce the same Risk Category.

The Risk Category and the location are then used to determine the design wind speed based on published wind-speed maps, available in Section 1609.3, figures 1609 A to C of the IBC, or Section 26.5.1, figures 26.5-1 A to C of ASCE 7-10. It can be difficult to read these maps to select the appropriate wind contour line, specifically along the East Coast. The Redwood City, Calif.-based Applied Technology Council (ATC), a non-profit that advances engineering applications for hazard mitigation, has digitized the maps providing a valuable resource for determining design wind speeds by GPS coordinates or the building’s address. Visit ATC’s wind-speed website. Note however that it is always advisable to cross check this design wind speed with the maps in the adopted code or with the local building authority.

PHOTOS: MIRO INDUSTRIES INC.

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Coating a Roof? Don’t Forget Fire Ratings

Fire tests are one of the most important system tests for roof coatings, and it is essential when specifying and applying a coating over an existing roof in a maintenance or repair setting to ensure the roof system’s fire rating is not negatively affected.

TEST METHODS FOR FIRE TESTS

The International Building Code (IBC), first published in 2000, brought together several regional codes into one central, national code and facilitated the acceleration of code adoptions across the U.S. Today, most of the U.S. follows a statewide adoption process for the IBC for Roof Assemblies and Rooftop Structures; some areas do not, which can make code enforcement tricky. Some areas still follow local adoption and may refer to older versions of the code instead of the most current 2012 IBC.

According to the most recent IBC, roof assemblies and coverings are divided into classes A, B, C or “Nonclassified” and are tested in accordance with UL 790 or ASTM E 108. These tests measure the spread of flame, recording whether the material you put on the roof will cause the flame to spread too far on the roof. The UL 790 inaugurated modern fire tests about 100 years ago and, as such, incorporates a century of data and history about roof coatings that may broaden the reach of what certifications the test provides.

“Many see UL 790 as the preferred fire test,” notes Steve Heinje, technical service manager with Quest Construction Products LLC. “It is interesting to note the ASTM E 108 test is deemed by the code requirements an equivalent test.” The ASTM E 108 is a consensus version of UL 790 and can be run by any qualified and accredited test laboratory. Many test laboratories, such as FM Approvals, conduct testing using ASTM E 108.

COMPONENTS OF FIRE TESTING

The roof coating is just one component in the fire rating of a roof assembly; other components include slope, the coating substrate, whether the roof deck is combustible and whether the roof is insulated. These factors, taken together, will determine the roof system’s fire rating.

SLOPE
Although there are exceptions, most fire ratings are done for slopes of under 3/4 inch for commercial roofs, and coatings tend to be recommended for application to a roof with 2 inches or less slope. Slope is an important factor to consider because special coatings may be needed for high slope transitions.

SUBSTRATE
The substrate or membrane type is another vital component of fire testing because the substrate to which the coating is applied could affect the flammability of the roof system. When coating over an existing roof, one should note what existing roofing substrate is being coated over—whether it’s BUR, mod bit, concrete, metal, asphalt or another type of substrate.

COMBUSTIBLE VS. NON-COMBUSTIBLE ROOF DECK
Most coatings are tested over noncombustible decks, but additional and challenging tests are required for the use of combustible decks. It is much more difficult to achieve a Class A rating when covering a wood deck.

INSULATION
Again, it is important to note the materials of the existing roof being coated because these components can affect the flammability of the roof system. Polymeric insulations often reduce the allowable slope for a given system.

PROPER APPLICATION OF THE ROOF COATING

Another significant consideration is that the coating is applied at the appropriate thickness and rate.

“One big thing out of the coating manufacturer’s control is that the applicator uses the recommended or test-required thickness and/or rate at the point of application,” points out Skip Leonard, technical services director with Henry Co. Proper application encompasses parameters, such as the final dry-film thickness, the use of granules or gravel, use of reinforcements and even the number of coats. Accounting for these details is an integral part of installing a rated system.

Once assembled, the roof covering will be granted a Class A, B or C rating by approved testing agencies, typically through UL 790 or ASTM E 108, depending on how effective the roof proves to be in terms of fire resistance. Rated coating solutions exist for just about any existing roof system recover or coating application and often can achieve a Class A rating.

Learn More
Visit the Roof Coatings Manufacturers Association website to locate a roof-coating manufacturer who can help you choose a roof coating most appropriate for your roof system. For more information about roof-coating fire ratings, check out FM Approval’s RoofNav online database for up-to-date roofing-related information or the UL Online Certifications Directory.

Against the Wind

The city of Moore, Okla., recognizes it cannot keep doing things the way they’ve always been done. You may recall on May 20, 2013, an EF5 tornado did extensive damage to the town. The new residential construction codes are based on research and damage evaluation by Chris Ramseyer and Lisa Holliday, civil engineers who were part of the National Science Foundation Rapid Response team that evaluated residential structural damage after the May 2013 tornado.

“A home is deconstructed by a tornado, starting with the breaching of the garage door,” Ramseyer explains. “The uplift generated by the wind causes the roof to collapse until the pressure pulls the building apart. These new residential building codes could possibly prevent that in the future.”

The new codes require roof sheathing, hurricane clips or framing anchors, continuous plywood bracing and windresistant garage doors. Moore’s new homes are required to withstand winds up to 135 mph rather than the standard 90 mph.

Although the city of Moore deserves to be commended for passing a more stringent building code less than one year after the 2013 tornado, this wasn’t the first damaging tornadic event Moore had experienced. The town also made national headlines in 1999 when it was hit by what was then considered the deadliest tornado since 1971. Moore also was damaged by tornadoes in 1998, 2003 and 2010. In my opinion, it was time for the Moore City Council to do the right thing by its citizens.

As extreme weather events occur more frequently, more emphasis is being placed on commercial roof wind resistance, as well. Robb Davis, P.E., recently attended a continuing-education conference for civil/structural engineers that discussed changes in the 2012 International Building Code and the referenced ASCE 7-10 “Minimum Design Loads for Buildings and Other Structures”. During the seminar, it became clear to Davis that nobody is specifically responsible for the design of wind loading to rooftop equipment as defined in the IBC and Chapter 29 of ASCE 7-10. Therefore, Davis reached out to Roofing because he believes it’s important roofing professionals understand the code requirements for wind loading to rooftop equipment, how the load is determined and applied, and how the load is transferred to the building structure. Davis shares his insight in “Tech Point”.

As Davis points out in his article, by better understanding wind loads on rooftop equipment, roofing professionals will be even better positioned to lead the design and construction industry in creating more resilient roofs and, ultimately, strengthening the structure and protecting the people underneath.