Summary: Cost-Effectiveness Analysis of the Residential Provisions of the 2015 IECC for the State of Utah (Pacific Northwest National Laboratory (June 2015)


  • 96 building energy models using EnergyPlus v8
  • Incremental costs from several sources with local construction cost multiplier based on standardized methodology
  • 5% interest rate, 30-year mortgage, 10% down payment
  • Compared 2015 IECC vs “Utah IECC”

Prescriptive Building Thermal Envelope changes to the 2015 IECC vs “Utah IECC”

  • increased attic insulation (CZ 3, CZ 5)
  • improved skylight, window and door efficiency values (CZ 3, CZ 5, CZ 6)
  • increased wood frame wall, and basement wall insulation (CZ 3, CZ 5, CZ 6

Insulation Requirements Analyzed

Other changes Analyzed

  • Improved insulation for return air ducts in attics
  • Demand-activated controls for recirculating systems
  • Outdoor Air Temperature Setback Control for Hot Water Boilers
  • Reduced air leakage rate
  • Reduced duct leakage
  • 75% high efficiency lighting

Additional Code Requirements Analyzed


Economic Analysis: 2015 IECC is Cost Effective

  • The incremental cost to the builder ranges between $1,089 and $3,332 (depending on the building plan and location)
  • Reduces energy costs by $297/year or 23.9% on average
  • Home buyers realizes “positive cash flow” within 2 years (annual energy savings are greater than the higher down payment and mortgage costs when these costs are rolled into a 30-year mortgage)

New “Energy Rating Index” Performance Path

  • New voluntary “Energy Rating Index” performance was not analyzed
  • The ERI is supported by the Leading Builders of America as a more cost effective way to building energy efficient new homes