Big Energy Code Changes For Wood Design

New calculators and software make compliance with building codes quick and seamless.

The advantages of wood products in the built world are often overlooked when it comes to the material’s performance related to energy efficiency. Due in part to favorable characteristics such as wood’s natural thermal resistance and low embodied energy, excellent structural performance and constructability, builders can meet even the strictest energy requirements using wood.

 

 

Changes in the IECC

The requirements of the 2006 IECC are often used as the baseline to compare later editions. Between the 2006 and 2009 editions, the amount of insulation required in wood construction did not change, but with the 2012 IECC, large strides in efficiency were made.

Homes in Climate Zones 3 and 4, which range from Georgia to Maryland, now required foam insulation or 2×6 walls instead of the customary 2×4 walls with R-13 insulation. Alternative methods of achieving the required performance were suddenly of more interest so that builders could continue to use the typical 2×4 walls. In response, the American Wood Council (AWC) developed Design Code for Acceptance publication Meeting Residential Energy Requirements with Wood-Frame Construction (DCA 7).

It’s important to note that although there are also 2009, 2015 and 2018 editions of the IECC, the 2012 version was chosen for the DCA 7 because of its increased stringency in requirements. Since the 2012 edition, the insulation requirements for wood construction has stayed relatively constant, which often allows solutions for the 2012 IECC to also be solutions for the 2015 and 2018 IECC.

The wood products industry unsuccessfully objected to inclusion of certain provisions in the 2012 version, most notably those that prescriptively require the use of foam plastic insulation. Despite encouraging code developers to be impartial by not specifying products and allowing any material to compete and meet the stated requirements, provisions favoring foam plastic in certain climate zones remained. The 2012 code does, however, provide four alternative compliance methods in the residential provisions.

“Meeting Residential Energy Requirements with Wood-Frame Construction” Guide

The DCA 7 guide outlines the four main paths for obtaining compliance with the 2012 IECC, which differ in levels of simplicity and flexibility:

  • Prescriptive R-value path provides minimum R-values for insulation and U-factors for fenestration components of the envelope.
  • Prescriptive U-factor path is based on a table of prescribed U-factors.
  • Prescriptive Total UA path allows the thermal performance of each building envelope assembly to be adjusted relative to tabulated U-factors.
  • Performance path requires a full simulation of energy usage considering building envelope conductivity, solar heat gain, air leakage, mechanical ventilation, internal heat gain, and equipment efficiencies.

The method referred to as “Total UA” offers a flexible but approachable path for builders who want to continue using wood products while meeting increasingly demanding energy codes. This method provides for the continued use of traditional wood wall assemblies, including the superior structural performance that comes from the use of wood panels. Improved energy performance of glazing, ceiling and floor areas, for instance, can be used to reduce required opaque wall requirements, such as foam sheathing.

Free Energy UA Calculator

AWC developed a free mobile- and tablet-based application to streamline the process of ensuring new and existing buildings comply with the latest building codes.

The Energy UA Calculator gives an opaque wall U-factor for the Total UA alternative compliance method permitted by the 2012 IECC or International Residential Code. The U-factor indicates the rate of heat loss of a wall assembly. The lower the U-factor, the greater a wall’s resistance to heat flow and the better its ability to control heat loss. The Energy UA Calculator is consistent with AWC’s DCA 7. The app also gives insulation requirements needed in various wood wall assemblies to achieve the specified opaque wall U-factor.

At the end of the day, constructing energy-efficient buildings saves builders and owners – and the nation – money and resources. There are many tools and much information available to those who would build with wood to achieve higher standards for energy requirements. And as building and energy codes continue to evolve and become more demanding, using wood products in the building envelope offers a viable option given the prescriptive construction methods presented in the DCA 7 guide to meet or exceed minimum requirements of the IECC.

To learn more and download these resources today, visit www.awc.org.

Loren A. Ross, P.E., is Manager of Engineering Research, American Wood Council.