I-Codes and Thermal Values
Since 2000, the I-Codes have served as models for almost all state and local building codes in the United States. The 2012 edition of the I-Codes includes several landmark advances in building energy efficiency and sustainability. Not only does the 2012 International Energy Conservation Code (IECC) include new and higher thermal standards for almost every roof and wall assembly, but these standards are further increased in the new International Green Construction Code (IgCC), which is intended to serve as an overlay code, or “above the code” standard for sustainable buildings. (For an overview of the I-Codes, see “Model Codes 101” on page 28.)
Why It Matters
The advancement of the levels of insulation matches the awareness and activities taking place, not just in the United States, but across North America and the world. Energy efficiency and the subsequent reduction of energy use is paramount in the building industry.
According to the U.S. Department of Energy’s Energy Efficiency and Renewable Energy website, “We spend more than $400 billion each year to power our homes and commercial buildings, consuming more than 70 percent of all electricity used in the United States, about 40 percent of our nation's total energy bill, and contributing to almost 40 percent of the nation's carbon dioxide emissions. And much of this energy and money is wasted — 20 percent or more on average. If we cut the energy use of U.S. buildings by 20 percent, we could save approximately $80 billion annually on energy bills, reduce greenhouse gas emissions, and create jobs.” (http://www1.eere.energy.gov/buildings/about.html)
Additionally, reduction of energy use by upgrading insulation amounts in our commercial and residential buildings also has significant co-benefits.
• Comfort and saving money are important to building occupants and owners. Added comfort in a commercial building means increased productivity and happier occupants, and that can mean higher occupancy rates.
• Upgrading our existing building stock (e.g., improving the energy efficiency of roofs and walls) means numerous jobs are produced, and many of those jobs are local. Improving your building improves the local economy.
• There is less stress and more security of our energy grid. Using less energy to do the same amount of work (e.g., heating and cooling our buildings) means less need for additional utility infrastructure, reduced peak loads, and extends our use of precious natural resources.
• Using less energy reduces our pollutant output which is better for humans and the environment. Buildings account for 40 percent of the carbon dioxide emissions in the United States, 18 percent of nitrogen oxide emissions, and 55 percent of sulfur dioxide emissions. Human health is affected by pollution; energy efficient buildings help reduce pollution and therefore improve the health of the human population.
• It’s important to understand why it is so important to build better building envelopes—whether for new construction or renovations—so our focus is not lost. And, it’s also important to understand that improvements in our building envelopes can provide very significant secondary benefits for the occupants and owners of buildings.
Although these advancements in energy efficiency are critical to the design of the next generation of sustainable buildings and renovation of our current stock, the number of new options may be confusing to the non-expert. For starters, the I-Codes now embrace two separate levels of thermal performance: a minimum code level in the IECC and an above-the-code level in the IgCC. In addition, the IECC and the IgCC offer two distinct paths to determine roof and wall R-value, one based on International Code Council (ICC) standards and one based on American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) standards. In past code editions, the R-values resulting from the ICC and ASHRAE paths frequently were identical, but recent editions of I-Codes and ASHRAE standards contain a number of significant differences in R-value requirements. An important change to be aware of is that the 2012 IgCC no longer contains the traditional roof and wall R-value tables used in previous codes. As a result, it may be difficult to determine exactly what is the correct roof and wall R-value for a particular new building or renovation project.
Thermal Values in ICC and ASHRAE Standards
Although differences in prescriptive thermal values can be found between ICC and ASHRAE standards, it is important to recognize that ICC and ASHRAE are working together closely to make energy codes as consistent as possible. In fact, ICC and ASHRAE jointly signed a Memorandum of Understanding in 2006 formally recognizing their mutual contribution to advancing building safety and energy efficiency and committing to explore ways to optimize codes and standards development. As a result of this mutual agreement, recent energy-related I-Codes formally reference their corresponding ASHRAE standards as equivalent paths to code compliance. In the case of the 2012 IECC, ASHRAE 2010 Energy Standard for Buildings Except Low-rise Residential Buildings (ASHRAE 90.1-2010) is identified as an equivalent code and design approach, while the 2012 IgCC identifies ASHRAE 2011 Standard for the Design of High-Performance Green Buildings (ASHRAE 189.1-2011) as an equivalent approach. A recap of the I-Code and ASHRAE energy standards, their intended function and their relationship to each other is provided in Table A.
Although ICC and ASHRAE are working closely to harmonize and support building energy standards, minor differences may occur simply because the two organizations utilize separate development processes. Although ICC and ASHRAE incorporate many similar approaches to achieve consensus, the very fact that their development processes are convened at different times and locations virtually assures that some differences will occur. An example of how these differences may affect roof and wall prescriptive thermal values is illustrated in Table B. This table identifies the minimum R-value as identified by the four relevant ICC and ASHRAE approaches for one of the most common commercial roofing assemblies (roofs with insulation above deck) located in Climate Zone 6. (Milwaukee, Wis., would be a typical city in this climate zone.)
As illustrated in Table B, minimum R-values for this climate zone vary considerably, even between codes intended to be functionally equivalent. Although it would be reasonable to assume that the R-35 required by an above-the-code standard such as ASHRAE 189.1 would be higher than the R-20 or R-30 required by minimum code standards such as the 2012 IECC (R-30) or ASHRAE 90.1 (R-20), it is difficult to understand why the R-values in the two minimum code standards differ so significantly. Unfortunately, the R-value differences between the 2012 IECC and ASHRAE 90.1-2010 appear to be related to procedural problems and timing differences occurring during the development of these standards. In the case of ASHRAE 90.1, a successful appeal by the glazing industry involving prescriptive thermal values for windows effectively delayed the inclusion of prescriptive thermal value tables in the 2010 edition. As a result, ASHRAE 90.1-2010 was published with a reference to the thermal value tables in the previous edition, so the R-values remained low (R-20). Although it appears likely that ASHRAE will publish revised thermal value tables this spring with roof and wall R-values much closer to the current 2012 IECC, the current discrepancy serves as a good example of the differences that may occur due to separate development processes.
The IgCC Approach to Thermal Values
Table B also illustrates how the development process for both ICC and ASHRAE may result in not only minor variations in table values but also significant differences in the basic approach to determining R-value. While the previously-mentioned glazing industry appeal was working its way through the ASHRAE development process, the ICC was conducting final hearings for the 2012 IgCC. Although it would be difficult to conclude that the IgCC deliberations were directly affected by the ongoing dispute at ASHRAE, it appears that the ICC decided to take a new path in regard to prescriptive thermal values (and possibly avoid conflicts among industry stakeholders). Instead of including tables of thermal values for roofs and walls, the 2012 IgCC incorporates specific instructions for calculating these above-the-code values. To accomplish this, Section 605.1.1 of the 2012 IgCC provides the following instructions:
“The building thermal envelope shall exceed the requirements of Tables C402.2 and C402.1.2 of the International Energy Conservation Code by not less than 10 percent. Specifically, for purposes of compliance with this code, each U-factor, C-factor, F-factor and SHGC in the specified tables shall be reduced by 10 percent to determine the prescriptive criteria for this code.” (2012 IGCC Section 605.1.1)
Although this instruction is reasonably straightforward, it is important to note that R-value (or R-factor) is not mentioned. Instead, the mathematical reciprocal of R-value (U-value or U-factor) is referenced. This means that in order to identify the minimum R-value for a roof or wall assembly under the IgCC, the designer must first identify the minimum U-value in the 2012 IECC for the roof or wall assembly in question, reduce it by 10 percent, and then calculate the reciprocal R-value. As an example, in the case of the Climate Zone 6 example in Table 1, the minimum U-value for a roof with insulation above deck in Table 402.1.2 of the 2012 IECC is 0.0320. Next, applying the 10 percent prescribed reduction results in a new IgCC U-value of 0.0288. Finally, converting the IgCC U-value of 0.0288 into its reciprocal R-value results in an IgCC R-value of 35.7. A detail of the calculation is illustrated in Table C.
For a wall or roof assembly with insulation located only in one place within the assembly, calculating the appropriate IgCC R-values is relatively simple, even if a little confusing initially. However, for walls or roofs with insulation located in more than one place within the assembly, the calculation may become more difficult. As an example, wood and metal framed walls in almost all climate zones now require two separate locations for insulation: (1) insulation installed within the wall cavity (i.e., between the wood and metal studs), and (2) continuous insulation (referenced as “ci” within the 2012 I-Codes) installed on the exterior side of the wall cavity. Examples of cavity insulation and continuous insulation in wood and metal framed walls are illustrated in Figure 1.
A major problem in calculating the IgCC R-values for insulation in framed wall assemblies involves the physical limitation of the cavity portion of the wall. Because the depth of this cavity is determined by the size of the standard framing members (typically 3 ½-inch or 5 ½-inch wood or metal studs) and because current minimum IECC standards for cavity insulation effectively reach the maximum value possible for the established cavity depth, the required IgCC increase in R-value usually must be applied only to the continuous insulation portion of the wall. As an example, a wall framed with two-by-sixes incorporates a 5 ½-inch cavity typically insulated with R-20 glass fiber or similar material. Because the IECC minimum R-value for a wood-framed two-by-six wall in Climate Zones 1 through 5 is R-20, the increase in R-value (or decrease in U-value) required by the IgCC can only be applied as continuous insulation on the exterior side of the wall without increasing the width of the studs. In this case, the necessary additional R-value is approximately R-2, which can be achieved by installing a layer of continuous insulation board to the exterior side of the wall framing.
Finally, the calculation of IgCC R-values involves an additional confounding factor. The R-value tables in the IECC are not derived as exact mathematical reciprocals of the corresponding U-value tables. To illustrate using the previous example of a roof with insulation above deck in Climate Zone 6, the IECC R-value table lists a value of R-30, which compares to an exact mathematical U-value reciprocal of U-0.033. However, the corresponding U-value table in the IECC lists a value of U-0.032, which is slightly lower than the mathematical reciprocal. This difference can be attributed to assumptions regarding effective thermal values of other elements of the assembly such as air films and framing members which can increase or reduce overall U-value. Another way to explain this is that the IECC and ASHRAE U-value tables provide values for the complete assembly, while the IECC and ASHRAE R-value tables provide values for the insulation within the assembly. This means that although a simple mathematical conversion of reducing IECC U-value by 10 percent will yield the correct IgCC U-value, a similar mathematical conversion of the new U-value to the new R-value will not necessarily yield the correct result.
Fortunately, this difference between U-value and R-value is addressed in Normative Appendix A of ASHRAE 90.1, which provides adjusted equivalent insulation R-values for assembly U-values. As a result, the actual determination of insulation R-value for the IgCC requires an additional step of looking up the wall or roof assembly in ASHRAE Normative Appendix A and extrapolating the required insulation R-value from the listing of equivalent R and U values listed in the appendix. Again, drawing on our roof example in Climate Zone 6, the mathematically calculated R-value reciprocal of the IgCC U-value is R-37.7. However, an interpolation from ASHRAE 90.1 Normative Appendix A yields a slightly lower R-value of R-37.5. In this case the minor difference of R-0.2 can be attributed to air films above and below the roof assembly.
Summing it Up: R-Value Confusion
We now have identified several factors that may be very confusing to a building designer trying to determine the appropriate code-required insulation R-values. First, the thermal value requirements of the IECC or IgCC may differ from similar requirements in ASHRAE 90.1 or 189.1, which are intended to be functional equivalents. Next, determining the thermal value requirements of the IgCC is complicated and involves several steps to arrive at the appropriate insulation R-values. Finally, proper determination of roof and wall R-values requires additional understanding of the specific type of roof and wall assembly involved and as well as the correct climate zone for the project.
Cutting Through the Confusion: A New Design Guide
In an effort to improve understanding of these confusing and complicated prescriptive R-value requirements, two leading building organizations have teamed up to publish a simple and easy-to-use guide for building designers. This new guide, developed by the Center for Environmental Innovation in Roofing (CEIR) and the Polyisocyanurate Insulation Manufacturers Association (PIMA), provides a simple reference tool to help building designers make the best roof and wall insulation decisions for new and existing buildings. The Roof and Wall Thermal Design Guide specifically addresses the complexity of different prescriptive roof and wall thermal values in the 2012 I-Codes by providing an organized step-by-step approach to determining the climate-appropriate R-value for common roof or wall assemblies.
In order to increase the guide’s usefulness for the code novice, color graphics are employed to illustrate key energy concepts embodied in the I-Codes. First, a map of North America with color-coded climate zones is provided to help the user locate the appropriate climate zone. Next, graphic illustrations of each major type of roof and wall assembly referenced in the code are used to guide the user to the appropriate R-value tables. These illustrations not only direct the user to the appropriate R-value table but they also identify the correct location of insulation within the assembly. Finally, the illustrations are placed directly above color-coded R-value tables showing a side-by-side comparison of the different ICC and ASHRAE R-values referenced within the code.
The guide also simplifies the new International Green Construction Code by providing pre-calculated 2012 IgCC R-values for all roof and wall assemblies by climate zone. As a supplement to the calculation, footnotes to the tables provide the specific reference in the IgCC for making the calculation as well as a description of the steps involved.
Using the Guide
Using the CEIR / PIMA design guide is fast and easy. All the designer needs to do is follow these simple steps:
1. Select the climate zone. In addition to an illustrated map of all North American climate zones, the guide provides a link to detailed county-by-county climate zone information maintained by Pacific Northwest National Laboratory of the U. S. Department of Energy.
2. Select the roof or wall assembly. The guide provides prescriptive R-value information for the following major roof and wall assembly types as referenced in the I-Codes:
• Roofs with insulation above deck
• Attic and other roofs
• Wood framed walls
• Metal framed walls
• Mass walls
3. Select the model code path. The guide provides separate R-value tables for the following I-Code and • ASHRAE standards:
• 2012 IECC
• 2012 IgCC
• ASHRAE 90.1-2010
• ASHRAE 189.1-2011
4. Look up the R-value. After the appropriate R-value table is located, the correct R-value may be determined by cross-referencing the relevant I-Code /ASHRAE standard with the appropriate climate zone.
Limitations of the Guide
The CEIR/PIMA Roof and Wall Thermal Design Guide achieves its simplicity and ease-of-use by narrowly focusing on one aspect of the I-Codes while not addressing many other important requirements. The specific prescriptive thermal values for wall and roof assemblies provided by the guide are required only if the energy efficiency of the building is not determined using approved energy modeling software. Although many new buildings are designed using such software, the use of prescriptive standards is still used frequently for smaller buildings and for building retrofits, especially re-roofing projects. In addition to building thermal design requirements, building projects must comply with all other relevant code requirements, especially life safety requirements. As a result, many wall and roof assemblies must incorporate structural, fire, wind and seismic design requirements not shown in the simple illustrations of this guide. Finally, the guide does not cover other important thermal design requirements for roofs and walls, including the use of “cool” roof surfaces in the warmest climate zones and the use of roof and wall air barriers. However, many of these additional requirements are discussed in the introduction to the guide or footnoted below the R-value tables in the guide.
In addition to a narrow focus only on prescriptive R-values, the guide also focuses only on the most common types of roof and wall assemblies used in conventional commercial building design. As a result, roofs and walls for metal buildings as well as below-grade walls have not been included in order to maintain simplicity.
One final limitation of the guide may be the most important. Although the I-Codes and related ASHRAE standards discussed within the guide are recognized to be national models for building energy efficiency, these codes and standards must be adopted formally by state and local jurisdictions, typically by legislative statute or mandated code adoption process. As a consequence, some states may have adopted a version of the 2012 I-Codes, while other states may continue to recognize earlier versions. Although some jurisdictions may not have adopted the 2012 I-Codes, it is usually prudent and best to use the most up-to-date design information when designing new building or renovating existing buildings. In addition, each state and municipality adopting the I-Codes may include revisions or amendments to the code that may change the prescriptive R-value requirements as shown in this guide. Some states and municipalities also may adopt only the ASHRAE version of the code to be the prevailing standard. Finally, the new “green” above-the-code standards of the IgCC and ASHRAE 189.1 may be adopted by states and municipalities to apply only to certain building projects, such as public facilities rather than private buildings.
Drilling down to the specific requirements of any specific state or municipal code jurisdiction is obviously beyond the scope of such a basic guide. However, a very useful online reference for state and local code requirements is sponsored and maintained by the Building Codes Assistance Project, a Washington-based nonprofit. This reference is the Online Code Environment and Advocacy Network, which can be accessed at http://energycodesocean.org/code-status-commercial Here, the building designer can select any state from an interactive U. S. map and discover which model code has been adopted, what amendments (if any) have been enacted, and what procedures and timetables are followed to update the code.
Obtaining Your Copy
The Roof and Wall Thermal Design Guide is available for download at no charge. Simply go to the CEIR website (www.roofingcenter.org) or PIMA website (www.polyiso.org) and download your free copy! The new Roof and Wall Thermal Design Guide is one more way that the roofing and insulation industry is helping to make sustainable design and construction easier for everyone. On behalf of the Center and PIMA, I hope you’ll download your copy and share it with other building owners and designers in your market. AR+W
Model Codes 101
The International Code Council (ICC) is a membership organization whose mission is “to provide the highest quality codes, standards, products and services for all concerned with the safety and performance of the building environment.”1 Building Officials and Code Administrators International, Inc., International Conference of Building Officials, and Southern Building Code Congress International, Inc., founded the ICC in 1994 to develop a single set of codes to be used internationally, and certainly across North America. Prior to forming the ICC, the three founding organizations each developed a separate, regional-based building code. The motivation behind forming a single organization to develop a unified model code was an understanding that a pooling of resources and knowledge would better protect the health, safety and welfare of the public.
ICC publishes a broad spectrum of model codes, which include the International Building Code (IBC), the International Energy Conservation Code (IECC), and the International Green Construction Code (IgCC). The International Codes, or I-Codes, are developed through a robust consensus-based process that invites any interested stakeholder to submit a code change proposal. The proposals are reviewed at meetings attended by ICC code development committees and eligible voting members. Stakeholder proposals also form the basis of code development committees’ recommendations that are balloted to voting members.
I-Codes are updated and published every three years, with the most recent published in 2012. Once published, federal, state and local governments may adopt the codes at the jurisdictional level. Fifty states and the District of Columbia, in addition to many federal agencies, have adopted and enforce the I-Codes. The version, or year, of the I-Codes adopted may vary between jurisdictions and certain jurisdictions may choose not to adopt the most recent versions of the various codes. And jurisdictions can amend the model codes to adapt them appropriately to their jurisdiction.
International Building Code
The International Building Code (IBC) was first published in 2000 and applies to commercial and multi-family buildings. The IBC provides minimum requirements to safeguard the public health, safety and general welfare of the occupants of new and existing buildings and structures. The code is fully compatible with the ICC family of codes, including: International Existing Building Code (IEBC), International Fire Code (IFC), and the International Plumbing Code (IPC).
While the IBC maintains a heavy focus on safety with respect to the construction and design of a building, the code is comprised of multiple chapters, including:
• Building heights and areas.
• Foundation, wall and roof construction.
• Building occupancy classifications.
• Means of egress.
The IBC also makes extensive references to other I-Codes and recognized national standards.
In the majority of jurisdictions adopting the IBC, the code applies to the construction of new buildings and alterations to existing buildings. The IBC extends throughout a building’s useful life to include changes in use and demolition.
The IBC applies to all types of buildings and structures; however, a jurisdiction may elect to exempt a certain category of buildings from the building code or from certain provisions of the code. Typical exemptions include historic buildings or buildings owned by governmental bodies other than the local jurisdiction, like a federal courthouse.
International Energy Conservation Code
Commercial buildings in the United States account for approximately forty percent of all domestic energy consumed. The International Energy Conservation Code (IECC) was first published in 2000 to address the energy used by commercial buildings. The IECC’s scope includes new construction and additions, alterations, renovations or repairs to existing buildings, but does not render an existing building noncompliant if the building is lawfully in existence when the IECC is adopted.
The intent of the IECC is to “regulate the design and construction of buildings for the effective use and conservation of energy over the useful life of each building.”2 The code is structured with prescriptive and performance requirements. Prescriptive requirements allow ease of design and enforcement. Performance requirements can be more complicated; however, they allow the use of innovative approaches and techniques to achieve the goal of designing and constructing more energy-efficient buildings. The IECC is not meant to supplant the safety, health or environment requirements present in other codes or ordinances adopted by a specific jurisdiction.
Chapter 4 of the IECC sets forth the requirements for commercial building energy efficiency. The chapter sections address specific portions of the building, including:
• Building envelope (roofs, walls, floors, glazing, skylights).
• Building mechanical systems.
• Service water heating.
• Electrical power and light.
The IECC also establishes requirements for total building performance.
To determine the specific requirements of a commercial building, Chapter 3 of the IECC identifies eight climate zones for the United States, and instructions on assigning climate zones outside of the United States and its territories. The climate zones are illustrated in a map and are structured based on climate characteristics like moisture and humidity. The climate zones create important distinctions between regions and optimize the energy efficiency requirements for commercial buildings. It is easy to understand that an office building in Minneapolis, Minn., will be designed differently than a similar building in Miami, Fla.
The U.S. Department of Energy (DOE), through its Building Energy Codes Program, participates in the development of the IECC to cost-effectively reduce energy consumption in buildings. The United States does not have a national energy code or standard. However, DOE does provide states and local jurisdictions with technical assistance to help facilitate the adoption process at the jurisdictional level. Currently, 41 states have adopted a statewide energy code for commercial buildings. Increasing the number of states that adopt and update their energy codes is an important factor in reducing the amount of energy consumed. The Alliance to Save Energy estimates that stronger, more widely adopted energy codes could reduce our nation’s total energy use by seven percent and save approximately $25 billion annually in energy costs by 2030.
International Green Construction Code
With the growing popularity of “green” construction, the demand by the public and policy makers for codes that address sustainable construction in a comprehensive manner has risen. The ICC first published the International Green Construction Code (IgCC) in 2012 to meet this demand.
The IgCC is the first model code to include sustainability requirements for the building and site, addressing key issues from the design, construction and use of the building through its service life.
To publish the 2012 IgCC, ICC partnered with five cooperating sponsors that include the American Institute of Architects (AIA), ASTM International, ASHRAE, the U.S. Green Building Council (USGBC) and the Illuminating Engineering Society.
“The IgCC is a tool that, when adopted nationwide by states and communities, will create path for the United States to follow in cutting energy use in one of its biggest energy consumers – commercial buildings,” said AIA President Jeff Potter.
To create this path towards more sustainable commercial buildings, the 2012 IgCC is divided into twelve chapters. The chapter titles reference topics unique to green construction, including:
• Life cycle assessment.
• Material resource conservation and efficiency.
• Energy conservation, efficiency and CO2 emission reduction.
• Commissioning, operation and maintenance.
While many of the sustainability topics outlined above are commonplace in today’s green building rating system, the IgCC captures sustainable construction in a credible, enforceable code. The IgCC references existing codes and standards, including the IECC, the National Green Building Standard, and incorporates ASHRAE Standard 189.1 as an alternative compliance path.
The IgCC is intended to establish a baseline for sustainable design and construction, which is intended to be used as an “overlay code” to the existing codes like building or fire codes. The IgCC also offers flexibility to the jurisdiction adopting the code in order to meet specific conditions and goals. The code contains “core provisions” and “jurisdictional requirements” options that can be selected and customized.
Several jurisdictions have already adopted the code as a voluntary path. Scottsdale, Ariz., has adopted the code as a mandatory requirement for all new construction. States also have taken action. Rhode Island was the first state to adopt the IgCC for public facilities and Maryland has authorized the code for use by the Department of Housing and Community Development and local governments.
Even without adoption, building owners and designers are requesting and designing energy-efficient buildings, and they are using the IgCC to help make that happen.
In addition to improving the performance of commercial buildings, several studies have documented the economic benefits of green codes. According to the Green Jobs Study3 commissioned by the USGBC, adopting policies like the IgCC will support nearly 8 million green construction-related jobs in the United States. Importantly, these economic benefits can be realized without significant differences in the cost of construction for green and “non-green” buildings.4
To learn more about the IgCC, including access to a free webinar titled Green Building Codes 101: Navigating the Standards, codes, and rating systems, visit http://www.iccsafe.org/cs/IgCC/Pages/default.aspx?r=IgCC.
The development of the I-Codes is a continuous and rigorous process. The development process for the 2015 editions of the IECC and IgCC are already underway. For more information on these I-Codes and for the latest news from the International Code Council, visit the organization’s website, www.iccsafe.org.
