Andrew Scatizzi- Stick to the Basics in New Construction

Thousands of energy models for newly constructed single family homes is a treasure trove of information if you’re like me and have a zealous obsession with cutting kilowatt-hours. As the utility company, we pay monetary incentives to builders that construct homes above an energy baseline, which in 2017 was a mixture of codes and measures from 2009 and 2015 IECC, with the overall goal of cutting peak demand and electricity consumption. The one overarching theme after reading through thousands and thousands of REM/Rate files is that if you’re interested in building an energy efficient new home, the low hanging fruit from technology upgrades have been all about picked. As our energy codes and standards continue to rise, builders and their contractors can’t rely on just installing the newest technology widget or Energy Star certified equipment that comes on the market. A commitment to superior building practices and thinking in terms of the whole house are crucial to future energy savings.

When talking about energy efficiency, what comes to mind are the “big 3” – HVAC, insulation, and lighting. Of the 12.6k houses we incentivized in the Houston metro area, the homes had an average of 15.5 SEER, R-32 attic insulation, R-13.7 wall insulation, and 93% high efficacy lighting. The wall insulation and high efficacy lighting especially highlight the need to take a whole house approach of building science – if you have 2x4 construction, there simply isn’t more room in the wall cavity to install more fiberglass batt insulation. The next large improvement is either 2x6 construction, foam insulation that help with overall house tightness, or sheathing with a R-3+ value. Same with high efficacy lighting. The prices of LEDS have dropped so dramatically that their installation are essentially the standard. Of course, every LED lighting salesman in the country will tell you differently, but the numbers simply don’t back up any other conclusion. The attic insulation number is also deceiving, because we have several builders who do encapsulated attics with R-21 foam insulation, so the average fiberglass insulation being installed is R-38, a high number that quickly gets into diminishing returns territory for large scale builders looking at adding any more R value in the attic.

The (relatively) high SEER ratings being installed for HVAC units here is another warning sign for the energy conscious builder. The amount of energy saved based on the SEER number isn’t linear – the delta in efficiency between 14 SEER and 16 SEER is much, much greater than the delta in efficiency in a 16 SEER and 18 SEER, and it declines even more the farther up the scale you go. As far as HVAC goes, production builders are running out of options to squeeze more energy savings simply from technology installations. Designs incorporating mini splits is about the only significant upgrade from an 18 SEER unit and there are still some consumer reservations about the aesthetics of the technology.

So, what should be made a priority if you’re a builder and you already have robust insulation, high efficacy lighting, and an efficient HVAC system? The best indicator of a well performing house after the “big 3” is air leakage which is measured by the house’s infiltration value. In our climate zone, homes that have a <3 ACH value at 50 pascals perform, on average, 10-15% better house than their <4 ACH counterparts. Building a home with a tight thermal envelope that creates a boundary between conditioned and unconditioned space doesn’t require expensive new equipment, but an eye for detail in rough in and a project manager willing to hold the workers and subs accountable. The homes submitted in our program that have a high SEER, high efficacy lighting, robust insulation, and a well-sealed thermal barrier easily perform 20-40% better than a house built to standard IECC codes, and are paid much higher monetary incentives as a result. As purchasing managers and builders look at what’s the next big thing in home construction, an eye for the basics of air sealing may benefit them the most.

—Andrew Scatizzi

Andrew Scatizzi is a program manager at Center Point Energy.

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Comment by David Butler on February 12, 2018 at 3:43pm

Given the location referenced in the article (southern Texas), I was surprised by what was not mentioned... windows!  In cooling dominated climates, glazing represents the largest load by far and it doesn't cost much if anything to shave an additional 10 - 15% off the prescriptive SHGC (i.e., specify 366 instead of 272, or similar, referring to Cardinal's surface-3 low-e coatings).

Even more can be saved -- often at little or no additional cost -- through smart design, e.g., favorable solar orientation, and strategic overhang geometry. In hot climates like Houston, it's all about keeping direct sunlight off the glass.

Regarding walls: In any climate, cost-benefit is much greater for adding R4 continuous (standard for stucco cladding systems) to 2x4 walls than for framing 2x6 16 on-center (due to reduction in thermal bypass). But my preferred wall is 2x6 built 24-oc with blown-in blanket or cellulose in the cavities, plus a climate-appropriate layer of exterior insulation. The additional cost of the 2x6 cavity insulation is largely offset by a reduction in lumber and framing costs.

Last but not least... get the ducts out of those hot, vented attics! Encapsulation isn't necessarily the best way to get there.

Comment by William Collins on February 12, 2018 at 10:33am

Yes....I read that post. I was just curious specifically what was happening in TX. Thanks for the link.

Comment by Michael Schettine on February 12, 2018 at 10:26am

http://information.insulationinstitute.org/blog/building-tighter-ho...

Above is a new solution that will get you 3 ACH . Nice post.

Comment by William Collins on February 12, 2018 at 10:16am

Andrew, are you seeing most builders trying to achieve the 3 ACH? 

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