Deep Energy Retrofit: What is it, and is it necessary?

Lately you have probably seen the term “deep-energy retrofit”— a phrase being thrown around with other words like “sustainability” and “green.” Like the word “green,” the term “deep-energy retrofit” is poorly defined and somewhat ambiguous. In most cases, though, “deep-energy retrofit” is used to describe remodeling projects designed to reduce a house’s energy use by 50% to 90%. Remodelers have been performing deep-energy retrofits— originally called “super insulation retrofits”—since the 1980s. Most deep energy retrofit projects are predominantly focused on reducing heating and cooling loads, not on the upgrade of appliances, lighting, or finish materials. While a deep-energy retrofit yields a home that is more comfortable and healthful to live in, the cost of such renovation work can be astronomical, making this type of retrofit work impossible for many people in this country. Those of us who can’t afford a deep-energy retrofit can still study the deep-energy approach, using it to shed light on more practical and cost-effective measures to make any home tighter and more efficient.

How deep?

There is no established legal definition of a deep-energy retrofit, but the term generally refers to retrofit measures that reduce a home’s energy use by 50% to 90% below that of a code-minimum house—or, according to a more lenient definition, below preretrofit levels. Probably fewer than 100 homes in North America have completed deep-energy retrofits that conform to the strictest definition of the term. A deep-energy retrofit doesn’t make sense in all climates, and not every home is a good candidate for the work. Cold-climate homes have higher energy bills than homes in a hot climate, so a cold-climate home is a better candidate than a home in a hot climate or a home that already has low energy bills. A house with a simple rectangular shape and a simple gable roof is easier and less expensive to retrofit than a house with complicated exterior elevations, bay windows, dormers, or a roof full of hips and valleys. Intricate architectural details add to the difficulty of such retrofit work, driving up costs.

Because many deep-energy retrofits require existing roofing and siding to be replaced, the best candidates for deep-energy retrofit work are houses that are in need of new roofing and siding.  The payback Homeowners who undertake deep-energy retrofits are usually motivated by environmental or energy-security concerns rather than a desire to save money on their energy bills. These jobs are so expensive—in the range of  $50,000 to $150,000 per house— which a homeowner would have to wait decades before the investment could be recouped. There’s no easy way to calculate the payback period for many deep-energy retrofits, in part because a major overhaul of a building’s shell inevitably includes many measures (for example, adding new siding or roofing) that aren’t energy related. Although these elements don’t make a significant contribution to a home’s energy performance, they may greatly enhance the home’s aesthetics and value. Those of us without a Midas budget will need to settle on a less ambitious approach to energy savings than a full-blown deep-energy retrofit, and that’s OK. Less expensive and less invasive retrofit measures, typically referred to in the industry as weatherization, have payback periods of 15 years or less.

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