The Minnesota Energy Code: A State Of Confusion?

States must comply with the U.S. Energy Conservation and Production Act (ECPA), which requires that commercial building codes meet or exceed the standards set forth by ANSI/ASHRAE/IESNA Standard 90.1.  These requirements address the design of the building envelope, lighting systems, HVAC systems, and other energy-using equipment. Minnesota’s current commercial energy code became effective on June 9, 2009 and adopts ASHRAE Standard 90.1 2004 with amendments.   All commercial structures and high-rise residential buildings in areas that have adopted and enforce the code are required to comply with the state commercial energy code using one of three compliance paths as outlined by ASHRAE 90.1: 1) Prescriptive Option (i.e. Tables 5.5-6 or 5.5-7);  2), Trade-Off Option (i.e. COMcheck); or 3) Energy Cost Budget Option (i.e. whole building modeling).

The Problem:  Where’s the exterior insulation?
We have noticed a number of commercial projects employing steel-framed wall assemblies without continuous outbound insulation.  Assuming compliance path #1, the Prescriptive Option, we would expect to see continuous R-3.8 at the exterior face of these assemblies as required by ASHRAE 90.1 2004 (Tables 5.5-6 and 5.5-7).

Perhaps compliance is achieved through path #2, the Trade-Off Option, which offers a more flexible and cost effective compliance path.   The Trade-Off Option employs the simulation software COMcheck to achieve trade-offs in thermal performance of building envelope components as long as the minimum performance criteria are met.  But according to the Minnesota Department of Labor & Industry (Inquiry #2011-02), COMcheck is not yet available for Minnesota’s current commercial energy code.  Moreover, the minimum thermal performance for the referenced steel-framed construction is not met.  For example, the maximum U-Factor for a steel-framed wall is 0.084, but Table A3.3 of ASHRAE 90.1 indicates a U-Factor of 0.109 for steel-framed walls with R-19 cavity insulation.   Either way, our steel-framed construction does not comply using the Trade-Off Option.

Our last compliance option involves an Energy Cost Budget, which would entail a robust analysis using building energy simulation software.   While some of these projects may be utilizing whole-building modeling, we know first-hand that many do not.

We can only speculate regarding the apparent disconnect between current mandates and enforcement practices.  But it is clear that energy initiatives are missing the mark on basic design requirements of ASHRAE 90.1.


  1. Whole Building Design Guide: Energy Codes and Standards
  2. Department of Energy: Building Energy Codes Program – Minnesota