Article #158 - Three Aproaches to Residential Compliance

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 are typically 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.

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 now 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.

The REScheck software can be downloaded at no cost.

A performance approach (also known as a systems performance approach) allows you to compare your proposed design with 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, photo voltaic cells, thermal energy storage, and fuel cells. This approach requires an annual energy analysis for the proposed design and the reference design.