In this issueNew This WeekNewsletterSustainable Design

Investing in Energy Efficiency

Energy efficiency takes on larger role as builders compete for buyers who value conservation

By Don Neff

Energy efficiency in a home design can increase comfort and reduce energy use and utility bills as well as increase the property value. Homebuyers are looking at sustainable options for cost efficiency and health reasons and to help protect the environment for the future. In response, builders are creatively embracing sustainability and new technology solutions. These concepts incorporate energy efficiency, resource conservation, automation and can include different levels of integration. Here we explore several such features, products and practices. 

Re-Engineered Practices

Re-thinking building envelope insulation is one of the keys for success. Long established practices of using fiberglass batt insulation by itself in 2×4 framed wall cavities will not provide enough R-value to achieve the stated goal, depending upon the climate zone. Improper installation can create convective air flow loops in interior walls that result in under-insulated assemblies and thus more energy usage. This leads to added expense for the homeowner. 

The insulation standards have been raised by the stakeholders, and in the process, the industry is moving towards higher performing rigid exterior foam products. Rigid foam boards can be used to insulate almost any part of the home, from the roof down to, and including, the foundation. Dr. Joe Lstiburek of Building Science Corp in Westford, Mass. shared the following quote at one of his recent Building Science Summer Camps: “When you are cold you pull on a sweater, you don’t eat it,” in comparing exterior rigid insulation with interior batt insulation stuffed into stud bays. A further benefit is that exterior rigid insulation eliminates thermal bridging and interior cold spots in the building. The U.S. Department of Energy estimates that they provide up to two times greater insulation than most other materials of the same thickness. 

Variations of this thermal control layer include combinations of interior (stud bay cavity) spray foam and fiberglass batt insulation. Blown in fiberglass fibers (“Spider insulation”) is another product, applied in the same way that damp-spray or wet-spray cellulose is installed. The key considerations with any of these solutions are the labor and material costs, availability of products and ease of installation. However, regardless of the type of insulation used, it needs to be installed by skilled and experienced tradesmen who understand the thermodynamic processes of insulated walls and roofing systems. 

TIGHTER ENVELOPES

Homebuilders are constructing progressively tighter building envelopes to achieve energy conservation objectives such as that in California with a goal of maximizing energy efficiency while minimizing building system defects. Use of blower door testing is commonly used to identify air and energy leaks, and thus provide guidance to implement proper sealing of the envelope.

In addition, improperly installed roofing systems are particularly vulnerable because most of the components are out of sight and consequently create longer term performance issues through air and vapor infiltration with potentially resultant building assembly deterioration. When homebuilders integrate better water, vapor and thermal control layers in their roofing systems, construction quality, durability and energy efficiency can improve. Windows and doors are similarly prime suspects in energy losses because they are really just big holes in the walls, filled with dissimilar materials of lower performance specs than the adjacent assemblies. Other contributory factors (of energy losses) are incorrect installations, not following architectural plan details, broken window seals and even the wrong window types selected for the specific climate zone.

SENSORS

We all know about plug loads creating excess electrical demand and occupant behavior causing aberrations in home operating systems, and both can unravel the most sustainably designed and constructed healthy home-work environment. With feedback loops, we have metrics to measure brewing problems, which can lead to a subtle deterioration of indoor air quality or potential long-term deterioration of the home. 

What to measure? Sensors which measure temperature, humidity, moisture level, water leaks, hot spots, cold spots, mold growth, carbon dioxide (CO2), volatile organic compounds (VOCs), monoxide (CO), supply and usage of site-generated solar energy and battery charge levels are just a few examples. The integration of these sensors into a data hub or dashboard—either centralized at one workstation, distributed throughout on a room-to-room basis or both—is also important. The dashboard can provide immediate feedback to understand occupant affects, system function and overall performance of the home.

Examples of a power usage dashboard have been demonstrated by Southern California Edison show variable costs in real time when several appliances automatically turn on and off throughout the day, either in parallel or in series. Measuring this cost will help occupants adjust their behavior to schedule usage during off-peak pricing periods. These advanced systems can also include the programming of home maintenance activities into the system, with maintenance alerts, monitoring for compliance and tracking completion with automated recordkeeping. Such a robust online customer service system could then be a game changer for sustainable building practices. 

SUMMARY

Whatever measures are taken, the goal of building energy efficient homes is to compete in the marketplace with state-of-the-art architectural designs and construction methods combined which take advantage of renewable energy systems. By doing so, builders can construct and sell homes that consumers want, and our environment needs.

Don Neff is President of LJP Construction Services. He can be reached at www.ljpltd.com.