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INTRODUCTION Every three years, the International Building Code (IBC) is revised and updated to incorporate new knowledge and experience gained within the design and construction community. As buildings account for more than one-third of the energy usage and nearly two-thirds of electricity consumption in the United States (epa.gov/greeningepa), it is important to design and construct more efficient buildings to reduce

these numbers. The 2012 IBC will require the implementation of the 2012 International Energy Conservation Code (IECC) which has incorporated more stringent performance requirements than the previous edition for new and existing buildings. The 2012 IECC is in the process of being adopted by each state in the United States. Figure 1 shows the status of State Energy Code Adoption as of May 2014. Some individual states have adopted stricter requirements than

Changes to the 2012 International Energy Conservation Code (IECC) with Respect to Commercial Building Envelopes

‒ by Rex A. Cyphers, P.E. Jodi Knorowski, E.I.T.

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those found in the 2012 IECC. This article presents some of the changes in the 2012 IECC as they relate to the building envelope. GENERAL CHANGES The 2012 IECC was restructured to separate Commercial and Residential Provisions. Previously, these provisions shared the same general requirements, administration, enforcement, and references. As separate provisions, these are better tailored to the specific building type. Commercial buildings must comply with one of the following to meet the requirements of the 2012 IECC: ASHRAE 90.1; Sections C402 (Building Envelope Requirements), C403 (Building Mechanical Systems), C404 (Service Water Heating), C405 (Electrical Power and Lighting Systems) and C406 (Additional Efficiency Package Options); or Section C407 (Total Building Performance) including the mandatory requirements of Sections C402 through C406 in order to provide a building energy cost less than or equal to 85% of the standard reference design building.

Introduction

General Changes

Figure 1. Status of State Energy Code Adoptions as of May 2014 (http://www.energycodes.gov)

July 2014

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The 2010 edition of ASHRAE 90.1 (Energy Standard for Buildings Except Low-Rise Residential Buildings) is referenced by and serves as the technical backbone for the Commercial Provisions of the 2012 IECC, as opposed to the previously referenced 2007 edition of ASHRAE 90.1. Many of the changes in this standard have been incorporated throughout the 2012 IECC, but additional details are included in the ASHRAE 90.1-10 standard. BUILDING ENVELOPE requirements Over the years, the IECC has required increasingly more stringent performance requirements for fenestration and cladding in an effort to increase energy efficiency of commercial buildings. These include the thermal performance of opaque walls and fenestrations along with the requirements of a continuous air barrier in certain climate zones and limits on air infiltration of doors and windows.

Thermal Performance Heat can be transferred through three primary mechanisms: conduction, convection, or radiation. Conduction is the transfer of heat through direct molecular contact. The rate of heat transfer is a function of a material’s thermal resistance and its thickness. The thermal resistance is typically expressed in terms of the R-value. Convection is the transfer of heat through the movement of molecules – basically air currents. Convection can become a significant issue when there is a discontinuity in the air barrier or excessive air leakage of fenestrations. Heat loss through convection can be magnitudes greater than heat loss through conduction. Radiation is the transfer of heat through electromagnetic waves through air, or a gas or vacuum. Solar radiation through fenestration can be measured by the Solar Heat Gain Coefficient (SHGC).

R-Value: The thermal resistance of a material is expressed as its R-value. It is typically an indication of how well the interior of the building is insulated from

the exterior and one of the main contributing factors to energy efficiency of the building. The Code has increased the minimum R-value requirements for the insulating materials in walls and roofs over the years and has added a continuous insulation requirement to reduce the effects of thermal bridging and to reduce the thermal gradient across framed cavities, which generally reduces the potential for condensation within the cavity. It is important to fully evaluate the amount and location of insulation within the wall assembly through a detailed hygrothermal analysis to ensure condensation or other moisture related problems will not occur. More insulation is not always the solution and in some cases can be detrimental to performance. Table 1 highlights some of the changes in the minimum R-value requirement from 2006 to 2012.

U-Factor: The U-factor is a measure of thermal transmittance and can provide a more holistic indication of an assembly’s

Building Envelope Requirements

2006 IECC 2009 IECC 2012 IECC

Roof Minimum R-value - Insulation Above Deck

15 ci 20 ci 25 ci

Roof Minimum R-value - Insulation in Attic or Other

30 38 38

Mass Wall Minimum R-value 5.7 ci 9.5 ci 9.5 ci

Metal Framed Wall Minimum R-value

13 13 + 7.5 ci 13 + 7.5 ci

Maximum U-factor (Fenestration)

0.40 w/out Metal; 0.50 Metal CW/SF; 0.85 Metal Doors;

0.55 All other Metal

0.40 w/out Metal; 0.50 Metal CW/SF; 0.85 Metal Doors;

0.55 All other Metal

0.38 Fixed; 0.45 Operable;

0.77 Doors

Table 1. Commercial building envelope requirements (Climate Zone 4)

ci = Continuous Insulation: Insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings. (ASHRAE 90.1)

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thermal performance, while the R-value only accounts specifically for insulating materials within the assembly. A lower U-factor indicates a higher thermally performing assembly. The U-factor can be considered as an alternative for opaque assemblies in order to meet the requirements for minimum R-values. The U-factor is more commonly seen when evaluating fenestration assemblies. The maximum U-factors for fenestration have been reduced in the 2012 Code and are no longer material dependent. Previously, metal framed doors and windows could have higher U-factors than other materials. Now, U-factor requirements are categorized by fixed fenestration, operable fenestration, and entrance doors. Table 1 compares the maximum U-factor requirements for fenestration between the 2006, 2009, and 2012 IECC.

Solar Heat Gain Coefficient: The SHGC is a ratio of how much of the sun’s energy is transferred to the interior of a building via fenestration and accounts for energy transferred both directly through the glazing as well as energy that is absorbed and subsequently emitted. The SHGC can contribute to increased cooling loads while reducing the heating loads in buildings. The lower the SHGC, the less solar heat is being transmitted. The SHGC must be adjusted based on the Projection Factor (PF) and the direction in which the fenestration faces relative to true north. The PF is a ratio between the length of any shading devices and the vertical height of glazing. Previously, the direction in which the fenestration

faced was not considered. The base SHGC remains unchanged in the 2012 IECC; however, this base value is applicable when the PF is less than 0.20 rather than 0.25 previously. For any PF greater than 0.20, an adjustment factor must be applied to the SHGC.

Roof Reflectance and Emittance The 2012 IECC has added roof reflectance and emittance provisions for low-sloped roofs directly above cooled, conditioned space in Climate Zones 1 through 3. A Climate Zone map of the United States is shown in Figure 2. These roofs must comply with one or more of the following:

Three-year aged solar reflectance of 0.55 and three-year aged thermal emittance of 0.75,

Initial solar reflectance of 0.70 and initial thermal emittance of 0.75,

Three-year-aged solar reflectance index of 64,

Initial solar reflectance index of 82.

Several exceptions are provided in the Code for portions of the roof

that are covered by components such as photovoltaic systems, roof gardens, and HVAC systems, roofs that are shaded during the peak sun angle, and roofs that are ballasted. Continuous Air Barrier The 2009 IECC simply required that “Openings and penetrations in the building envelope shall be sealed with caulking material or closed with gasketing systems” (502.4.3). The 2012 IECC now requires that “A continuous air barrier shall be provided throughout the building thermal envelope” (C402.4.1) and provides several sections of requirements for the air barrier. The continuous air barrier is permitted to be located on the inside, outside, or within assemblies of the building envelope. The continuous air barrier must satisfy the stipulated construction requirements and compliance options. The only exception to the continuous air barrier requirement is for those buildings located in Climate Zones 1 through 3.

Construction Requirements (C402.4.1.1): The continuous air barrier is to be constructed such that it is continuous for all

Figure 2. Climate zone map (http://www.aamanet.org)

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assemblies of the building thermal envelope, all joints and seams must be sealed, all penetrations must be sealed, and all recessed lighting fixtures within the building thermal envelope must be sealed to limit air leakage.

Compliance Options (C402.4.1.2): The continuous air barrier must comply with one of the following three options: 1. Materials must have an air

permeability no greater than 0.004 cfm/ft2 (0.02 L/s·m2) under a pressure differential of 0.3 inch water gage (75 Pa) when tested in accordance with ASTM E2178.

2. Assemblies of materials and components must have a combined average air leakage not to exceed 0.04 cfm/ft2 (0.02 L/s·m2) under a pressure differential of 0.3 inch water gage (75 Pa) when tested in accordance with ASTM E2357, ASTM E1677, or ASTM E283.

3. The completed building must have an air leakage rate not to exceed 0.40 cfm/ft2 (0.02 L/s·m2) under a pressure differential of 0.3 inch water gage (75 Pa) when tested in accordance with ASTM E779.

In addition to the continuous air barrier requirements, the 2012 IECC also requires more stringent air

leakage requirements for fenestration assemblies. Several of these requirements are highlighted in Table 2. SUMMARY Energy codes continue to tighten performance requirements for the building envelope. The increased minimum R-value for some building assemblies and decreased U-factors limit the amount of heat mitigating into and out of the building envelope. The adjustments to the SHGC provide a simplified approach while still allowing for flexibility based on building orientation and climate zone. The combination of the continuous air barrier and reduced air leakage requirements in fenestration assemblies will help prevent air movement between the interior and exterior space, which will limit the potential for condensation, frost, corrosion, and microbial growth issues. By preventing the loss of heat and air through the building envelope, the size of HVAC systems can be reduced. The changes implemented in the 2012 IECC are intended to further reduce energy usage and improve energy efficiency.

DEFINITIONS Building Thermal Envelope: The basement walls, exterior walls, floor, roof, and any other building elements that enclose conditioned space or provide a boundary between conditioned space and exempt or unconditioned space. Continuous Air Barrier: A combination of materials and assemblies that restrict or prevent the passage of air through the building thermal envelope. Projection Factor (PF): The ratio of the distance measured horizontally from the furthest continuous extremity of any overhang, eave, or permanently attached shading device to the vertical surface of the glazing to the distance measured vertically from the bottom of the glazing to the underside of the overhang, eave, or permanently attached shading device. R-Value (Thermal Resistance): The inverse of the time rate of heat flow through a body from one of its bounding surfaces to the other surface for a unit temperature difference between the two surfaces, under steady state conditions, per unit area (h·ft2·°F/Btu) [(m2·K)/W].

Summary

Definitions

Fenestration Assembly 2006 IECC 2009 IECC 2012 IECC Test Reference (2012 IECC)

Windows (cfm/ft2) 0.30 0.30 0.20* AAMA/WDMA/CSA101/I.S.2/A440 or

NFRC 400

Curtain Walls & Storefronts (cfm/ft2)

0.30 0.30 0.06 NFRC 400 or ASTM E 283

at 1.57 psf (75 Pa)

Swinging Doors (cfm/ft2) 1.00 0.50 0.20* AAMA/WDMA/CSA101/I.S.2/A440 or

NFRC 400

Table 2. Maximum air infiltration rate for fenestration

*Maximum air infiltration rate is permitted to be 0.30 cfm/ft2 when tested at 6.24 psf in accordance with the test reference indicated.

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Solar Heat Gain Coefficient (SHGC): The ratio of the solar heat gain entering the space through the fenestration assembly to the incident solar radiation. Solar heat gain includes directly transmitted solar heat and absorbed solar radiation which is then reradiated, conducted, or convected into the space. U-Factor (Thermal Transmittance): The coefficient of heat transmission (air to air) through a building component or assembly, equal to the time rate of heat flow per unit area and unit temperature difference between the warm side and cold side air films (Btu/hr·ft2·°F) [W/(m2·K)].

ANSI/ASHRAE/IES 90.1, 2010, Energy Standard for Buildings Except Low- rise Residential Buildings.

Building Energy Codes Program, U.S. Department of Energy, http://www.energycodes.gov/

Greening EPA, U.S. Environmental Protection Agency, http://www.epa.gov/greeningepa

International Energy Conservation Code and Commentary, 2012, International Code Council.

International Energy Conservation Code, 2009, International Code Council.

International Energy Conservation Code, 2006, International Code Council.

International Building Code, 2012, International Code Council. 

References

Does Your Project Require Building Envelope Fenestration Testing?

WDP performs laboratory and field quality assurance and diagnostic testing. Our field testing equipment can be mobilized quickly on project sites to perform compliance testing for windows, curtain walls, masonry, stucco, and other exterior wall systems. Our services can also be used to evaluate performance problems associated with water leakage, excessive air infiltration or exfiltration, or other common post occupancy-related failures in window, wall, waterproofing, and roof systems. Contact Kevin Pearson, Associate kpearson@wdpa.com (703) 257-9280

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Information & Insight is an informational publication designed and intended to provide general information on topics, which may be of interest to our readers. The publication is not intended to provide specific engineering or legal advice. Every project has unique characteristics that should be evaluated in context of the work to be performed and, where prudent, should include review and input by legal counsel. Whitlock Dalrymple Poston & Associates, Inc. is a consulting engineering firm specializing in evaluation, renovation, and repair of existing structures, geotechnical engineering, and construction services. With offices located in Virginia, New York, and Texas, WDP is well positioned geographically to service projects throughout the United States. For assistance with existing or future projects, please contact our closest office at your convenience.

Manassas, Virginia A. Rhett Whitlock, Ph.D., P.E., Principal Gerald A. Dalrymple, P.E., Principal Robert J. Niber, P.E., Senior Associate Robert F. Scheller, P.E., Senior Associate Matthew J. Innocenzi, P.E., Senior Associate Kevin Pearson, Associate Charlottesville, Virginia Rex A. Cyphers, P.E., Senior Associate Blacksburg, Virginia J. Eric Peterson, P.E., Principal New York, New York Keith E. Kesner, Ph.D., P.E., S.E., Senior Associate Austin, Texas Randall W. Poston, Ph.D., P.E., S.E., Principal

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