Focus on the Envelope

Home owners and builders seldom give the building envelope the priority it deserves. The insulation, air barrier, windows, and doors are the most important features of a new home. These envelope features determine a home’s energy efficiency and comfort. They’re also permanent and may never change.  Homes with better thermal resistance and airtightness need smaller HVAC systems. The HVAC system performance matters less in an energy-efficient home compared to a conventional home.

Envelope Efficiency Competes with Other Priorities

Wise homeowners or builders build homes that are more efficient than the current energy code. They focus on energy efficiency, comfort, and durability and de-emphasize other preferences.

  • Large size and complex style of the home’s envelope.
  • Expensive fireplaces, decks, window coverings, kitchen finishes, floor coverings, and light fixtures.
  • Complexity and expense of the home’s HVAC system: ground-source heat pumps and radiant floors, for example.

HVAC: More Interesting than Insulation but…

Foundation and wall of a zero-energy home.

Foundation and wall of a zero-energy home.

The HVAC system are certainly an important building component. And, home owners and builders seem more interested in HVAC than in thermal performance. However, we believe that the envelope’s thermal performance is more important than HVAC.

Our Recommendations

Establish an energy target for your new home. Give the designer flexibility to optimize the efficiency-and-comfort benefits of the envelope and HVAC system. Hire an energy rater to provide quality control. The rater can suggest a HERS Index that fits the ambitions of the designer, builder, and home owner.
If you want to be energy-efficient, comfortable, and environmentally conscious, don’t build a too-big or too-complex home. Don’t spend too much on your HVAC system. Set your HERS Index goal for 50 or less. Current energy codes require around a HERS 90. The best builders achieve HERS Indexes of near zero.