For some designers, an ideal energy code would tell them exactly what they need to do for their building. For other designers, being told exactly what they need to do might be viewed as limiting their creativity. Energy codes attempt to cater to both types of designers by offering multiple compliance paths within the code.
BECP’s Commercial Buildings for Architects Resource Guide (Resource 1) states the issue as
An energy code’s format can significantly influence design, sometimes more than the actual requirements. A prescriptive code clearly states what applies, but may limit design freedom and foster the view that the building is composed of separate, non-related systems. A performance-based code provides more design freedom and can lead to innovative design but involves more complex energy simulations and tradeoffs between systems. Smaller commercial buildings with singular HVAC, service hot water, and lighting systems are more likely to be designed using a prescriptive approach. Larger commercial buildings that have multiple systems or varied uses and loads provide more opportunities to follow a performance-based code.
The 2009 IECC and ASHRAE Standard 90.1-2007, as well as the 2012 IECC and ASHRAE Standard 90.1-2010, contain a number of compliance paths. The Choosing an Energy Code Compliance Path Topic Brief (Resource 2) presents these paths in more detail.
Each compliance path may have mandatory, prescriptive, or tradeoff requirements. These terms are defined below, along with a few other terms related to compliance paths.
Mandatory requirements are requirements that must be met in every building design no matter which compliance path is chosen.
Prescriptive requirements are requirements that either must be met by every building design, or if the requirement is not met, a tradeoff must be made to “make up” for not meeting that requirement.
Envelope tradeoffs are tightly defined tradeoffs that allow trades to be made between various parts of the building envelope. An example might be that a building owner might choose to install more insulation in the roof to “make up” for putting in more window area than the code allows. ASHRAE Standard 90.1-2007/2010 provides the basic rules for this envelope tradeoff, and that tradeoff is implemented in the COMcheck™ software. A simpler envelope tradeoff is found in the 2009/2012 IECC for low-rise residential buildings in the “UA” tradeoff approach implemented in the REScheck™ software. Both of these DOE-developed software tools are available free of charge on this website. The 2009/2012 IECC allows you to trade off levels of insulation and glazing efficiency. For example, trade decreased wall efficiency (lower R-value) for increased window efficiency (lower U-factor), or increase the roof insulation and reduce or eliminate slab-edge insulation.
Deemed-to-comply software is software that implements major elements of an energy code, and which may be approved by a code official or authority having jurisdiction—whatever level of government adopted the code. Because Chapter 5 of the 2009 IECC and Chapter C4 of the 2012 IECC do not include specific mention of an envelope tradeoff for commercial buildings, but the 2009/2012 IECC does allow use of ASHRAE Standard 90.1-2007/2010, which does have an envelope tradeoff, the COMcheck software implements the envelope tradeoff even for the 2009/2012 IECC. COMcheck therefore does not implement all compliance options in the 2009/2012 IECC and is referred to as deemed-to-comply software for the IECC. COMcheck is also deemed to comply with ASHRAE Standard 90.1 because COMcheck does not fully implement the space-by-space envelope requirements in ASHRAE Standard 90.1. The REScheck software is a close implementation of the IECC but is not specifically mentioned in the IECC and is therefore deemed to comply as well. Resource 3 provides a discussion of which jurisdictions allow the use of COMcheck and REScheck on a state-by-state basis. Whole building tradeoffs, also known as the systems performance approach or just the performance approach, implement tradeoffs that can be made between various building systems based on rules set in ASHRAE Standard 90.1 and in the IECC as applicable. An example might be that a building owner might choose to install more efficient lighting than the code requires to “make up” for putting in less insulation than the code allows. This approach allows you to compare your proposed design to a baseline or reference design that exactly meets code requirements. If the proposed design is at least as efficient as the baseline in terms of annual energy use, it complies. This approach allows greater flexibility but is more complicated, although software has been developed to assist code users. A performance approach is often necessary to obtain credit for special features, such as passive solar design, photovoltaic cells, thermal energy storage, and fuel cells. The Building Energy Software Tools Directory (Resource 4) lists tools that can be used to do an annual energy analysis of a building. The rules for these calculations are found in the 2009/2012 IECC performance alternative, or the ASHRAE Standard 90.1-2007/2010 Energy Cost Budget Method. REScheck offers a limited performance approach for low-rise residential buildings.
It is also important to note that when an energy code has multiple compliance paths within it, a building designed to one compliance path may have different energy efficiency measures to one designed under a different compliance path. Developers of energy codes typically attempt to keep the overall stringency of the compliance paths more or less the same in terms of energy or energy cost, but there are variations between paths. Resource 2 provides some discussion on why a designer might want to consider particular compliance paths within a code.