December 30, 2016
The International Code Council (ICC) concluded its Group B Public Comment Hearings on October 25, 2016, in Kansas City, Missouri. The results of this code cycle finalize the changes that will form the 2018 edition of the International Codes. The Group B hearings included the following:
International Building Code – Fire Safety
- International Building Code – General
- International Building Code – Structural
- International Existing Building Code
- International Energy Conservation Code
- International Fire Code
- International Residential – Building
Code proposals that received public comments were on the agenda for the hearings. There were a number of very contentious code proposals, the most significant of which was the adoption of ASCE 7-2016, Minimum Design Loads for Buildings and Other Structures. Changes in the wind provisions from the 2010 edition to the 2016 edition significantly increase component and cladding pressures and change roof loads for low-slope roofs.
The reasoning of the American Society of Civil Engineers (ASCE) was thus:
The ASCE 7-16 wind provisions have four primary areas of impact on construction cost: reevaluation of wind speeds; separate mapped wind speeds for Risk Categories III and IV; updated wind pressure coefficients for components and cladding on low-rise, low-slope roofs; and new wind pressure coefficients for silos, tanks, and similar structures. As part of the development of new wind speed maps, a new national wind hazard study was undertaken, taking advantage of the greatly increased number of wind reporting stations now available. This study separately evaluated hazards due to tornadoes, hurricanes, and thunderstorms, as well as other sources and also accounted for increased deforestation and urban growth. The resulting wind hazard maps for Risk Category II and III structures generally reduce design wind speed hazards. For Risk Category II structures, this reduction is on the order of 10 to 15 miles per hour, resulting in a reduction of wind pressures for the design of building frames in the range of 20% to 30% or more, depending on location. This represents perhaps a 2 to 3% reduction in construction cost, broadly, across the U.S. A somewhat smaller reduction is achieved for Risk Category III structures. With the introduction of new maps for Risk Category IV structures, wind speeds essentially remain unchanged, resulting in no net cost impact.
Wind pressure coefficients for low-slope roofs less than 60 feet in height changed significantly. In most of the U.S., this increase is offset by the reductions in wind speeds described above and results in no net cost impact. However, significant impact does occur in hurricane-prone regions, within 600 feet of where wind pressures on roofing can increase by nearly 40%. This results in, perhaps, a 2% increase in total building construction cost for those few cases. It should be noted that failure of roofing has been observed in most hurricane events, resulting in substantial financial losses. These new requirements will reduce such financial losses in the future. Similarly, the new wind pressure coefficients for silos, tanks, and other cylindrical structures result in small cost increase.1
Lee Shoemaker, representing the Metal Building Manufacturers Association (MBMA), submitted a proposal to add to the exceptions in determining wind loads in Section 1609.1.1 of the International Building Code (IBC). Shoemaker’s reason:
The wind load for roof components and cladding need not be greater than 1.3 times the corresponding wind load determined using ASCE 7-10. …The internal pressure coefficient is only one of six factors that are used in calculating wind pressures. The other five factors include wind speed (V), directionality factor (Kd), internal pressure (GC), topographic factor (KZt), and velocity pressure exposure coefficient (KZ).
The ASCE 7 debate did not focus on whether the roof component and cladding GC values were, in fact, greater, based on the latest wind tunnel tests, rather than on the resulting wind loads. It did not seem realistic that we were underestimating design wind loads on roof components and cladding by a factor of more than two in some cases. For example, fasteners in the field of a gable roof with a roof slope between 7 and 20 degrees would see the negative GC value increase from -0.9 to -2.0. If, in fact, we have been under-designing by a factor of two (well over the typical factor of safety), there would have been more widespread performance issues raised over the years associated with a design wind load deficiency rather than the most common failure issues that are sporadic and most often associated with poor quality of construction. The question raised was: Are there conservatisms in the other factors and systematic biases that have been offsetting the GC pressure coefficients? The resounding answer to that question from the ASCE 7 Committee was yes, absolutely. But, the debate was a philosophical one that divided the committee into two camps. Some said we know there are probably other conservatisms and the wind loads aren’t as high as they will be with the proposed GC revisions, but we will start with GC and address the other factors in subsequent revisions. Others said that piecemeal approach would increase construction costs too severely, given the lack of performance issues. It was not a resounding decision – a swing of one vote would have changed the outcome.
This proposal would cap the wind load on roof components and cladding to 30% higher than those that we are currently designing for. This is still a substantial increase, but it is felt that would be a prudent compromise while the other conservatisms are studied in the next cycle of ASCE 7. Several industry groups, including MBMA and the American Iron and Steel Institute (AISI), have committed funding to begin these studies. It is felt this would be the reasonable approach and this would also even out the severe swings in the wind loads from one cycle to the next that would ensue.2
The Single Ply Roofing Institute (SPRI) submitted a similar proposal that added an exception to Section 1609.1.1 that would allow the use of calculated wind loads for roof components and cladding using ASCE 7-10.
J.C. Harrington, assistant vice president for engineering standards at Factory Mutual, was approached about how FM plans to handle the new edition of ASCE. FM did not make any changes to its standards and data sheets to reflect changes in the 2010 edition of ASCE-7. Harrington stated FM is considering changing its safety factors rather than following ASCE 7-16.
The IBC Structural Committee first heard the proposals in the committee action hearings in March. The committee is comprised of representatives of code officials, practicing engineers and architects, the National Institute of Standards and Technology (NIST), and the National Home Builders Association (NHBA). The initial vote on Shoemaker’s proposal resulted in a tied vote. The chair then broke the tie by voting to disapprove Shoemaker’s proposal.
At the final action hearings, governmental voting members vote on the proposals online, and the results are posted on ICC’s remote access program, cdpACCESS. With the cdpACCESS, voting results at the hearings are not included in the vote count. In other words, the only valid votes for the final action hearings are the votes that are cast online during a two-week period after the conclusion of the final action hearings.
Results: The ASCE submittal was approved as submitted. The Lee Shoemaker proposal was disapproved, and the SPRI proposal was withdrawn.
Ballasted Roofs in High Wind Areas
Since creation of the IBC, there has been an ongoing debate about ballasted roofs in high-wind areas. Currently, Section 1504.8 of the IBC states, “Aggregate used as surfacing for roof coverings and aggregate, gravel,
or stone used as ballast shall not be used on the roof of a building located in a hurricane-prone region…or any other building with a mean roof height exceeding that permitted by Table 1504.8, based on the exposure category and basic wind speed at the site.” This code cycle, the Single Ply Roofing Industry (SPRI) introduced a proposal that would revise Table 1504.8 to specify the gradation of the stone as per ASTM D1863 and ASTM D7655 and modify parapet requirements. By grading the stone and reviewing wind tunnel testing performed with aggregate roofs, the requirements of
the table would be relaxed by allowing larger-stone aggregate to be allowed in higher wind speed areas than currently allowed.
Results: The proposal was approved with some modifications as a result of public comments.
The Asphalt Roofing Manufacturers Association (ARMA) submitted a proposal that would allow buildings outside the windborne debris area to use aggregate when a parapet is designed by a registered design professional and using an approved parapet design.
Results: This proposal was withdrawn prior to the final voting.
There was also a proposal spearheaded by NIST that would not allow the installation of aggregate, gravel, or stone on buildings located in areas that have potentials for 250-mph winds and which are on risk Category III or IV buildings as in accordance with ICC 500. ICC 500, Standard for the Design and Construction of Storm Shelters, includes a map entitled “Shelter Design Wind Speeds for Tornadoes” and shows the areas in the Midwest that have the potential for wind speeds of 250 mph. Risk Category III buildings include buildings with more than 300 occupants, certain institutional
occupancies, and some educational occupancies; and Risk Category IV buildings include hospitals, as well as fire, rescue, ambulance, and police stations. NIST has been charged by Congress to be the lead agency for the National Windstorm Impact Reduction Act. As the name implies, the act requires that a plan be developed to reduce the impact of windstorms. This was the first code proposal associated with the program.
Results: Disapproved. The Structural Committee stated it doesn’t make
sense to restrict aggregate on roofs using wind speed criteria that haven’t been used in the design of the building.
Design Guides or Standards?
For several code cycles, SPRI has attempted to have several of its standards added to the code. ANSI/SPRI WD-1, Wind Design Standard Practice for Roofing Assemblies; BSR/SPRI RP-14, Wind Design Standard for Vegetative Roofing Systems;
and BSR/SPRI GT-1, Test Standard for Gutter Systems, were again proposed during this code cycle. Opponents argued that the standards are design guides and do not provide prescriptive requirements.
Results: None of the proposals were approved.
Labeling of Ice Dam Protection
ARMA submitted a proposal that will require self-adhered modified-bitumen sheets and adhered underlayments to bear a label indicating compliance with ASTM D1970, Standard Specification for Self-Adhering Polymer-Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection.
Results: This proposal was approved.
Historically, the third year of the code cycle has been devoted to hearings for the International Green Code (IGC). ICC and ASHRAE, the publisher of ASHRAE 189.1, Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings, have signed a Memorandum of Understanding to use the 189.1 standard for the technical provisions of the IGC, so there will be no IGC hearings in 2017. The code hearings will resume in 2017 with the Group A hearings.
- ICC Complete Monograph, 2016 Group B Public Comment Agenda.