The condition of a building envelope is critical to energy efficiency, living comfort and even indoor air quality. In past eras of low energy costs, building methods and materials permitted a higher amount of air exchange with the outdoors. Insulation standards, meanwhile, were lower. Most of these houses are still standing and, unless they’re updated to today’s energy realities and comfort expectations, the owners are putting up with needlessly high operating costs and poor heating/cooling performance. Here’s a brief overview of how aspects of the building envelope affect your indoor environment:

Air LeakageGentry Heating and Air Conditioning

Cracks and gaps in the envelope let unconditioned air in and conditioned air out. Some leakage is built in due to the lax tolerances and non-energy efficient construction of the past. In other cases, it’s due to simple wear and tear or the result of aging as building materials shrink and shift.

Air leakage can be reduced by:

  • Using caulking to seal gaps between the baseboard and floor, and the walls and ceiling. Also look for cracks along vertical wall joints. Openings into the attic around recessed ceiling lights or attic access stairs should also be sealed.
  • Outside, caulk along the joint between the exterior wall and the foundation. Fill larger, irregular gaps where pipes or other conduits enter the house with expandable spray foam.
  • Gaps around mating surfaces of doors and windows should be closed with weatherstripping. Weatherstripping has a finite service life and requires occasional renewal.


Insulation retards heat transfer through the building envelope by conduction or radiation. In summer, heat energy moves toward the cooler environment indoors, while during winter it tends to transfer outdoors. Insulation is what retards that transfer of heat energy. Because heat naturally rises, the amount and quality of attic insulation is most critical.

In Asheville’s climate zone, the Department of Energy recommends attic insulation in depths ranging fro 12 inches to 18 inches for fiberglass batts or 10 inches to 15 inches for blown cellulose.

Learn more about your building envelope from the pros at Gentry Heating Inc. or call 828-581-4045 to schedule an appointment.

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