The Energy Star program for homes requires a well-constructed thermal envelope/thermal enclosure. The thermal envelope consists of exterior walls, ceilings, and floors as well as windows and doors—anything that touches the outdoor environment. A well-constructed thermal envelope consists of high-performance windows, high-quality insulation, fully-aligned air-barriers, reduced thermal bridging, and effective air-sealing.
High-performance windows are well constructed, installed in accordance with manufacturers recommendations, are well flashed and waterproofed, are air-sealed between the window and framing, and have a NFRC sticker with all the required information attached to the window. Energy Star requires lower u-values, in more extreme, or colder, climates and lower SHGC values in warmer climates.
High quality insulation, simply, is insulation installed in a high-quality manner. Wall insulation touches a solid surface on all six sides. There are no gaps between the insulation and adjacent material. The insulation is installed so that it is perfectly compacted and installed per the manufacturer’s recommendations. Energy Star also requires more insulation, or a higher R-value, in more extreme, or colder, climates.
Energy Star requires fully-aligned air-barriers. An air-barrier is a durable, solid material that blocks air flow between conditioned space and unconditioned space. The air barrier must be at the same location as the insulation. Energy Star describes how air-barriers in a variety of problematic locations throughout a building, such as walls behind showers and fireplaces, knee walls, double walls, and all other walls should be constructed.
Reduced thermal bridging for above-grade walls can be accomplished in one of five ways:
- Continuous rigid insulation—The insulation covers the entire exterior of the sheathing.
- Structural insulated panels (SIP’s)—SIP’s consist of rigid insulation, bonded to OSB panels on each side of the insulation.
- Insulated concrete forms (ICF’s)—ICF’s consist of rigid insulation bonded to each side of a concrete wall.
- Double-wall framing—This type of framing consists of two rows of framing, separated by an air gap.
- Advanced framing—This type of framing entails using different framing techniques that result in more insulation and less wood.
Effective air-sealing is required by the Energy Star program. Penetrations to unconditioned space must be fully sealed with solid blocking or flashing; gaps must be sealed with foam or caulk. These penetrations, most often, are located at ducts, piping, wiring, fans, and lighting fixtures. Cracks in the building envelope must be fully sealed. These cracks are, quite often, located at sill plates, tops of walls, and openings around windows.
All of the construction techniques listed in this article result in better built, more energy-efficient homes. Homes constructed with these techniques will cost homeowners less to operate and be far more comfortable places to live.