Sam Rashkin is Chief Architect for the Building Technologies Office under the Office of Energy Efficiency and Renewable Energy for the U.S. Department of Energy. He is also the author of “Retooling the U.S. Housing Industry: How It Got Here, Why It’s Broken, and How to Fix It,”
a book detailing a plan to change the homebuyer experience.
Green Home Builder: What changes have you seen so far in 2016 regarding the move to more sustainable housing building practices?
Sam Rashkin: The biggest change I have seen in 2016 is a growing interest on the part of developers to lead the Zero Energy Ready Home (ZERH) movement. This includes Stapleton in Denver where a minimum of 10 percent of remaining 4,500 new homes in Phase 10 must be ZERH certified; Whisper Valley in Austin is the first phase of a 7,500 unit development where all the homes are required to include most ZERH requirements and full ZERH certification is being considered; Sterling Ranch outside of Denver is where 12,000 homes are being developed with requirements substantially aligned with ZERH. Additionally, our program has received commitments this year to certify all homes ZERH in developments across the nation ranging from 20 to 500 or more homes.
GHB: What impact does building newer homes with energy-efficient building envelopes have for the future of residential energy usage?
SR: Even homes built to minimum 2009 and 2012 International Energy Conservation Code have what would have been considered advanced building enclosures a short time ago. This includes advanced levels of insulation, air-tightness, and window performance. All builders need to realize that we’re in new territory when it comes to technical challenges. Homes have colder surface temperatures inside the cavity that demand diligent water management details. This is because better insulated and sealed enclosures have very low drying potential due to reduced thermal and air flow. Second, advanced enclosures impose very low heating and cooling loads. This results in substantially reduced air flow requirements and much longer swing seasons without the benefit of accidental dehumidification from air conditioning. Thus, optimized comfort systems with properly designed duct systems and humidity control are critical. Lastly, advanced enclosures are substantially more air-tight which makes comprehensive indoor air quality strategies with source control, dilution, and filtration no longer extra credit. So, the impact of energy efficient building enclosures is that building science just became mission-critical. If you are a builder, it is imperative to have an in-house or retained building science expert provide advice on all significant technical and design decisions.
GHB: California has made a statement to only build new Zero Net Energy homes by 2020. What are your top suggestions for homebuilders in CA and across the US to achieve this bold endeavor?
SR: My top suggestion in the drive to ever greater efficiency with zero energy codes is to never forget performance! Therefore, I highly recommend California and any other regions moving to zero energy codes adopt the Zero Energy Ready Home technical requirements as a platform for their codes. These requirements help ensure that performance factors inextricably linked to efficiency are also addressed, including comprehensive water management, optimized comfort systems, and a complete package of indoor air quality measures.
GHB: What steps is the US Department of Energy taking to encourage better HERS scores and better sustainability for newer homes in the US?
SR: Qualification for Zero Energy Ready Home ensures an impressively low HERS Index score. The minimum threshold scores without PV range from the high-40s to mid-50s depends on climate zone with the average actual score without PV of certified homes in the mid-40s. However, the key to remember is that the absolute HERS score is not the most critical goal—it’s the implementation of proven innovations and best practices. In fact, the HERS index score can vary significantly for the same bundle of improvements. So the steps being taken by DOE to drive down HERS scores is to make proven innovations from the Building America program mandatory requirements for Zero Energy Ready Home.
GHB: What emerging or existing trend in energy efficiency efforts for the housing industry are you most excited for?
SR: The energy efficiency trend that’s most exciting is the looming market readiness of ultra-efficient windows. This is because we have gotten the rest of how we construct thermal enclosures to be worthy of lasting hundreds of years. Advanced aerogel and vacuum insulated panels may reduce the thickness for a given R-value, but we already are building enclosures with ultra-efficient insulation. Further, we are routinely constructing ultra-air-tight enclosures including Passive Homes with 0.6 ACH50 or tighter performance. The last remaining thermal hole in enclosures is the window, and thermal holes significantly undermine the R-value assembly. ENERGY STAR® windows are still only about R-3. The R-7 windows out today and R-10 windows coming soon will completely transform the effectiveness of thermal enclosures in mixed and cold climates. Once ultra-efficient windows become ubiquitous, we will achieve true zero energy ready performance.