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Residential Compliance FAQs
- What is a prescriptive packages approach?
- What is a trade-off approach?
- What is a performance approach?
- Which approach is the best for a particular building?
- Do the three approaches provide different results?
- Why are there so many compliance approaches?
- Is it possible to use all these approaches in my state?
- What compliance tools and materials are available for these approaches?
- Where can I get these products?
Q: What is a prescriptive packages approach?
A prescriptive packages approach lists the minimum R-value or maximum U-factor requirements for each building component such as windows, walls, and roofs. This approach is quick and easy to use, but many users find it somewhat restrictive because the requirements typically are based on worst-case assumptions and all requirements must be met exactly as specified. By locating the correct climate zone and looking up the appropriate table of packages, you can verify that your project meets one of the packages listed for that climate zone.
See the REScheck Prescriptive Package Generator for the web-based version of this approach.
See the REScheck™ (formerly MECcheck) prescriptive packages for the paper-based version of this approach. The Prescriptive Package Field Guides are another quick reference for this method of compliance.
Q: What is a trade-off approach?
A trade-off approach allows you to trade enhanced energy efficiency in one component against decreased energy efficiency in another component. You can, 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. Typically, this method is less restrictive than prescriptive approaches because components that exceed the requirements can compensate for those that do not meet the code.
The REScheck software simplifies energy code compliance by automating the trade-off calculations for this approach. REScheck is available in both a desktop and online version. The desktop version, simply called REScheck, can be installed on both PC and Mac systems. The online version, REScheck-Web, performs just like the desktop version but requires no download or installation. Projects can be saved online and accessed from anywhere.
Q: What is a performance approach?
A performance approach (also known as a systems performance approach) allows you to compare your proposed design to a baseline or reference design and demonstrate that the proposed design is at least as efficient as the baseline in terms of annual energy use. This approach allows greater flexibility but requires considerably more effort. 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. This approach requires an annual energy analysis for the proposed design and the reference design. We do not offer residential software products at this time to comply using this approach, but future versions of the REScheck software will include the DOE-2 energy analysis engine to perform the necessary calculations needed to determine compliance.
Q: Which approach is the best for a particular building?
Choosing the appropriate approach depends on the complexity and/or uniqueness of the building and the amount of time and money available for demonstrating compliance. The prescriptive approach allows quick review of the requirements. If these requirements are too restrictive, try a trade-off approach. For example, if the window area of the building exceeds that allowed by the prescriptive approach, a trade-off approach might work. If nontraditional components are used or if energy use trade-off between building systems (e.g., envelope, mechanical) is desired, then use the performance approach.
Q: Do the three approaches provide different results?
Yes, they can. Performance approaches require a higher degree of detail so that an individual building can be designed to exactly meet the energy code requirements. Prescriptive approaches tend to be somewhat conservative and use worst-case default assumptions so the prescriptive packages are applicable to all buildings. Although the prescriptive approach may result in a more energy-efficient building because of its conservative assumptions, this result is not always the case. The prescriptive approach generally does not account for several features that affect energy use, such as the effect of window orientation and external shading on solar heat gain. Trade-off approaches fall somewhere between the prescriptive and performance approaches in both flexibility and complexity.
Q: Why are there so many compliance approaches?
Over the years, the code has grown to provide different approaches of varying simplicity and flexibility to meet user needs. The simpler approaches are less flexible but are generally easier to use. Some of the approaches have considerable overlap.
Q: Is it possible to use all these approaches in my state?
The Model Energy Code (MEC) (predecessor to the IECC) and the IECC contain requirements for all three approaches. If your state has adopted any versions of the MEC or IECC directly, you may be allowed to use all three compliance approaches. Check with your local jurisdiction to determine which approaches and compliance tools you can use.
Q: What compliance tools and materials are available for these approaches?
DOE provides free REScheck compliance tools for the trade-off approach and the prescriptive packages approach.
Q: Where can I get these products?
You can download REScheck compliance materials from this site.