An energy efficient house must be designed as a system of various components that interact with each other.
Controlling the flow of heat, air and moisture to make the home environment comfortable, safe, healthy,
durable and efficient are the goals.
With increasingly stringent energy code requirements (see our Savvy Special Report on Energy Codes), the home building industry is finally being forced to catch up with all of the building science and performance ideas that many on the front lines of sustainability have been talking about for years.
Doing an amortization calculation upfront, comparing the extra cost of systems and products needed, versus the savings on utility bills, can help your buyer decide on making energy upgrades that go beyond the baseline code. Generally, if you can show a payback in three to seven years, buyers will opt in if they can qualify. Energy Efficient Mortgage Programs factor in a homeowner’s efforts to conserve energy in the loan qualification process; other programs lend money to existing homeowners specifically to pay for energy efficiency upgrades.
To significantly reduce the use of energy it takes to heat and cool a home, or even get to Net Zero (where the home makes as much electricity on-site as it consumes over the course of a year’s time), requires some knowledge about building science, which revolves around physics. An energy efficient house must be designed as a system of various components that interact with each other. It typically is achieved via a team effort that includes an architect and a skilled contractor, along with an energy consultant who will build a model to predict the performance of the home, and a mechanical engineer, who will ensure you use the ideal mechanical equipment.
Air sealing is the easiest and most affordable way to make your home comfortable and energy efficient. Triple-glazed windows, super-efficient insulation and diligent façade details are some ways to seal up the cracks to meet and exceed the code requirements. Texas currently matches the model code for wood frame walls in Climate Zone 2– R-value minimum of 20, or R-13 cavity insulation plus R-5 continuous insulation (ci), while reducing the requirement to R-13 in Climate Zone 2. When we adopt the latest model codes, zero cavity insulation may be allowed when using R-15-rated ci.
Structural Insulated Panels (SIPs) made of a strong outer sheathing (OSB or cement board) with a foam core are an example of a whole wall system solution. R-values for SIPs depend on the thickness of the SIP and the type of core material that is used, but generally exceed building code requirements.
House wrap, along with properly installed insulation constitutes a successful application of continuous insulation (ci) crucial for creating a tight building envelope. Also known as “outsulation,” ci is continuous across all structural members without thermal bridges other than fasteners and service openings. While most house wraps do not have R-value, they help protect against loss of R-value in insulation due to wind washing. Foam Board (Rigid Foam Panels), are an example of ci that does add R-value. Typical foam boards rate between R-4 and R-6.5 per inch of thickness.
Opinions differ on the right combination of insulating products to use with the house wrap or foam board to get to the desired R-Value. High-performance (medium-density and high-density) fiberglass blankets and batts have R-values between R-3.7 and R-4.3 per inch of thickness. Blown-in insulation R-values range from R-2.2 up to R-3.8 for dense cellulose. Closed cell foam has the highest R-value of any insulation, around R-6.2 per inch; open-cell foam insulation is less expensive with values around R-3.7 per inch of thickness.
The next step in energy efficient home design is the specification of low-energy HVAC systems, appliances, and fixtures. For the HVAC, a professional versed at load calculations is essential. Oversizing can lead to poor humidity control, short cycling and wasted money.
It would be remiss not to mention the impact that Smart products play in the quest for Net Zero—ranging from your standard Smart thermostat to 3D infrared sensor technology that scans the room to detect temperature variations and occupants and adapts appropriately. Winning a Best of IBS® award, SPAN, founded by Arch Rao, former Head of Products for Tesla Energy, re-invents the connection point between the grid and your home—the electrical panel. By replacing the traditional electrical panel in the home with powerful smart technology, Span provides in-depth, circuit-level monitoring, optimization and control of everything in your home that uses power—from solar panels, backup generators and EV chargers to the everyday appliances in your kitchen.
Beautifully designed all black Solaria solar panels complement a home’s architectural style and enhance curb appeal.
SunPower’s panels and batteries prove that home solar systems no longer need to be an eyesore and can complement the aesthetics of the home.
The City of Houston now requires builders to make accommodations for solar panels in their design. While it does not require new homes to have solar panels, the Houston City Council’s mandate means the potential for their installation must be incorporated into their plans. Home designs will have to identify where on the roof the panels could go, ensure ventilation pipes or other hardware do not impede that space, leave a conduit from the roof to the electrical box for wiring, and allow space in that box in case a homeowner decides to pursue panels later.
Once you’ve reduced your electrical loads as much as possible in the design process, your energy model will determine how much electricity you could offset with renewable sources such as solar energy. With the increased focus on combatting climate change, many states, cities and counties are encouraging homeowners to deploy solar. The price of solar panels has decreased dramatically in recent years and PVs are becoming less visually obtrusive as well.
THE BOTTOM LINE: A Savvy Builder’s advantage can come from documenting the advantage of buying a high-performance new home over an existing one. The Residential Energy Services Network (RESNET) reported that the average Home Energy Rating (HERS) Index Score in 2021 was 58; this is 42 percent more efficient than homes built as recently as 2006 and 72 percent more efficient than a typical home built in the 1970s. It is estimated that by 2035, 75 percent of the building stock in our country will be new or renovated, with many of the renovation upgrades anticipated to be energy related.