Building Envelope/Shell

• Building shells—or envelopes—lose energy through thermal conductivity and infiltration, which are interrelated and require special attention during design and construction. 
• Pay close attention to design and construction of a building’s envelope to increase energy savings.

Building envelope improvements:

• reduce energy cost;
• improve comfort;
• reduce mold and moisture-related problems;
• reduce material degradation; and
• allow installation of smaller HVAC systems.

Thermal Conductivity

The ability of material or substance to conduct heat.

• Insulation - Insulation, such as fiberglass, cellulose, sprayed foam and rigid board products, can be applied to wall cavities and/or wall surfaces to reduce thermal conductivity. For detailed information on insulation products and installation, see DOE's Insulation Fact Sheet (pdf).

• Thermal Bridging - Designers work to minimize thermal bridges since they increase energy use, create moisture condensation and create non-uniform temperatures in conditioned spaces. Thermal bridges are areas that transfers more heat than surrounding areas.

  Many commercial and institutional buildings are constructed with steel. Steel is approximately 1,000 times more thermally conductive than fiberglass insulation. Adding just one inch of rigid Styrofoam insulation to the steel wall boosts its R-value nearly 50%.

• Thermal Bypass (convective looping) - Occurs when a gap exists between the air barrier and insulation, or no air barrier exists. Warm air in this space rises, while cool air drops, which creates a looping mechanism that transports heat out of the building when temperatures are cold outside and draws heat into the building during hot days.

Air Leakage

Air movement robs buildings of energy, transports moisture into wall assemblies and allows smoke, odors, dust and other pollutants into (or out of) the building. Leakage commonly occurs at:

• junctions of the wall/window/door interfaces or wall/roof/floor junctions; and
• any service penetrations.

Typical Air Sealant Foam Uses (PDF 608KB) outlines air-sealing opportunities in commercial buildings.

Air and Vapor Barriers

To control air movement, install a continuous air barrier (air flow retarder) on at least one side of the insulation.
A vapor barrier blocks water vapor. The Building Science Corporation lists classes of vapor barriers (pdf). Colorado's Front Range is classified as a cold climate where Class II vapor barriers are required on the warm side of all assemblies. Drywall with latex primer and topcoat (e.g. two coats of paint) is a Class II vapor barrier. In this case, the drywall would serve as the air barrier and vapor barrier.

Resources

• Air Barrier Association of America
• Building Science Corporation
• Sample wall details
• Brick Veneer Steel Stud - best practice guide
• Chapter 42, Building Envelopes - American Society of Heating, Refrigerating and Air-Conditioning Engineers