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2015 Washington State Energy Code: residential impact assessment

  • Date:
  • Author(s)/Creator(s):
    Poppy Storm
    Benjamin Hannas
    David Baylon
  • Publisher(s)/Producter(s):
    Northwest Energy Efficiency Alliance

For more than 30 years, the Pacific Northwest has successfully pursued state residential energy codes and building programs to create ever more efficient housing. Since its inception, the Northwest Energy Efficiency Alliance (NEEA) has played a pivotal role in aiding states to deliver more effective and efficient energy codes. NEEA contracted Ecotope to quantify the energy use, energy savings, and incremental costs for residential codes in Washington. Ecotope compared the 2015 and 2012 residential energy code for single-family (including townhomes) and low-rise multifamily units; low-rise multifamily units are defined as 3-stories or less.

The study objectives included:

  • Calculate average expected energy use per house (SF and MF) under the new Washington State Energy Code (WSEC). Heating systems included gas furnaces, gas furnaces with air conditioning, heat pumps, and electric resistance heat.
  • Calculate the incremental savings due to each code improvement for each heating type and climate for both SF and MF cases.
  • Estimate incremental new construction costs of the WSEC for both single-family and lowrise multifamily.

Comparison of 2012 and 2015 Code Provisions

The general structure and details of the 2012 and 2015 WSEC are very similar, with only a few changes in the options table, as detailed in Table 6 in the Appendix. The baseline requirements of the two codes are the same, except that detached one-family, detached two-family, and townhouses using zonal electric primary heating are required in 2015 to have a ductless heat pump installed.

The point requirement for the options table increased from 2012 to 2015. The quick summary is the points went from 1.5 points in 2012 to 3.5 points in 2015 for medium-sized units, which is the size of most new construction units. The requirements for small units (5000 SqFt) units increased from 2.5 points to 4.5 points. Table 5 in the Appendix shows the points requirements in more detail.

Energy Impacts

The analysis estimated incremental energy savings and costs for the most recent round of the WSEC change from 2012 to 2015. The estimates are a weighted average of all construction types, heating system types, and climates in a given category. Further, the estimates consider both the electric and gas site savings separately. Single-family units in Washington have more incidence of gas heating compared to low-rise multifamily, where electric resistance heat is most common, which explains why, on a per dwelling basis, there is more electric savings for multifamily than singlefamily. Overall this represents 10.6% of the estimated energy use of the homes built to the 2012 WSEC.

Cost Impacts

The costs in 2012 dollars include envelope measures, duct sealing, HVAC equipment upgrades, house sealing, and lighting upgrades. The numbers are the minimum first cost necessary to achieve the code changes pertaining to energy consumption in the building. These costs were derived from the analysis of the Washington State Department of Commerce and the standard cost tables use by the Regional Technical Forum (RTF).

Northwest Energy Efficiency Alliance
Policy Quality
Sustainable building design and construction
Building energy codes
Energy consumption