Deep Energy Retrofit (DER) refers to the retrofit of the building enclosure and other building systems in a way that results in a high performance building. A successful DER will result in very low post-retrofit energy use and also provide benefits to building durability, comfort, and indoor air quality (IAQ). DER may also increase the usable space or amenity of a building. For example, retrofitting the thermal enclosure of attic or basement spaces may make it possible to expand finished living area into these spaces where it had not been possible before.
DER achieves performance on par with best-in-class new construction. That is, the performance resulting from DER will exceed new construction code standards and rival the performance of high-performance new construction. In fact, many of the techniques and strategies illustrated in this guide have been adapted from proven high-performance and super-insulation techniques used in exemplary new construction projects.
What levels of thermal performance constitute "high performance"? Years of helping builders, developers and designers to reach high performance goals involving tens of thousands of homes has led BSC to identify a set of performance targets for major building enclosures components. The set of performance targets is often expressed as "1.5-5-10-20-40-60" where 5 refers to the target R-value for windows and doors; 10, the target R-value for slabs; 20, the target R-value for foundation wall assemblies; 40, the target R-value for wall assemblies; 60, the target R-value of the attic/roof assembly; and, 1.5, the target air tightness of the building enclosure system measured in terms of air changes per hour at 50 Pascals (ACH50). These targets provide a framework for identifying high performance enclosures-enclosures that reduce the heating and cooling load of the enclosure system to a practical minimum. When we want to describe the performance goals for a DER enclosure, it suffices to use the expression "1.5-5-10-20-40-60". These are the levels of thermal performance that are represented in the guidance and illustrations contained in this guide.
While the enclosure measures in a DER are aimed at reducing heating and cooling loads, DER also addresses the mechanical systems that serve those loads. A comprehensive DER will also replace older and standard efficiency heating, cooling and water heating systems with efficient equipment configured to provide efficient performance.
Finally, since the essential purpose of the enclosure system as well as the heating and cooling systems is to allow users of a building to control the indoor environment, we cannot neglect the fundamental importance of air quality in the indoor environment. At the most basic level, we need to think of air quality as it pertains to life safety. It is also important to provide for control of moisture and dilution of contaminants through ventilation. A DER must provide robust combustion safety as well as effective mechanical ventilation (see Prerequisites for High Performance Enclosure Retrofit below).
A DER project need not be a comprehensive building enclosure renovation project. In fact, most DER projects address only one or two major components of the enclosure such as the roof or walls and windows or basement walls and slab. As a matter of health, safety and fundamental performance, the prerequisite for any DER project - even limited DER projects - will be to ensure combustion safety and to provide the means for effective ventilation.