Use of sunlight for daytime lighting needs. Daylighting strategies include solar orientation of windows as well as the use of skylights, clerestory windows, solar tubes, reflective surfaces, and interior glazing to allow light to move through a structure.

Measure of how cold or warm a location is over a period of time relative to a base temperature, typically 65°F (although other base temperatures, such as 75°F, can be used for cooling). To calculate the number of heating degree-days (HDD) of a given day, average the maximum and minimum outdoor temperatures and subtract that from 65°F. The annual number of heating degree-days is a measure of the severity of the climate and is used to determine expected fuel use for heating. Cooling degree-days (CDD), which measure air conditioning requirements, are calculated by subtracting the average outdoor temperature from an indoor base temperature.

Difference in temperature across a divider; often used to refer to the difference between indoor and outdoor temperatures.

Situation that occurs within a house when the indoor air pressure is lower than that outdoors. Exhaust fans, including bath and kitchen fans, or a clothes dryer can cause depressurization, and it may in turn cause back drafting as well as increased levels of radon within the home.

Reasonably expected minimum (or maximum) temperature for a particular area; used to size heating and cooling equipment. Often, design temperatures are further defined as the X% temperature, meaning that it is the temperature that is exceeded X% of the time (for example, the 1% design temperature is that temperature that is exceeded, on average, 1% of the time, or 87.6 hours of the year).

Company that handles house design and construction. Since both services are provided by the same firm, integrated design can often be more easily achieved.

In a forced-air heating/cooling system, the diffuser is a register or grille attached to ducting through which heated or air conditioned air is delivered to the living space. In a tubular skylight or an electric light fixture, the diffuser is a cover plate through which scattered light is delivered.

Type of passive solar heating system in which south-facing windows provide heat gain during the daytime and high-mass thermal-storage materials absorb and store that heat. At night, the stored heat radiates back out, warming the space. This is the simplest type of passive solar heating system, but careful design is required to prevent overheating.

Ventilation that uses natural convection to move warm air up and out of a building; used in Scandinavia since the 1970s, it is being increasingly employed in the United States.

Difference between day and night average temperatures.

True divided light sash have small panes of glass separated by muntins. Because large pieces of glass used to be difficult (or expensive) to make, older houses have windows with two, four, or six small lights per sash. These multiple-light sash are also called "divided-light sash" or sometimes "divided-light windows."

United States Department of Energy.

Construction system in which two layers of studs are used to provide a thicker-than-normal wall system so that a lot of insulation can be installed; the two walls are often separated by several inches to reduce thermal bridging through the studs and to provide additional space for insulation.

DHR, also known as graywater heat-recovery system. System that extracts heat from hot-water waste lines to preheat cold water before it reaches the water heater or tap; especially useful when paired with on-demand or solar hot-water systems.

Path that water would take over the building envelope. Concealed drainage-plane materials, such as building paper or housewrap, are designed to shed water that penetrates the building’s cladding. Drainage planes are installed to overlap in shingle fashion (weatherlap) so that water flows downward and away from the building envelope.

Air temperature as measured by an ordinary thermometer.

Underground structure that captures, then slowly releases storm-water runoff so that it can be absorbed by the soil.

Metal or plastic stops that are attached to framing at inside corners. The clips replace framing, thus leaving more room for insulation. Because such a corner floats (acting as a stop, the clip allows the first sheet of drywall to be trapped by the second, perpendicularly installed sheet), cracking of the drywall joint is less common.

Calibrated air-flow measurement system developed to test the airtightness of forced-air duct systems. All outlets for the duct system, except for the one attached to the duct blaster, are sealed off and the system is either pressurized or depressurized; the work needed by the fan to maintain a given pressure difference provides a measure of duct leakage.

A type of small-capacity heat pump (as little as a ton or even less) with a closely-associated outside compressor and inside evaporating coil (often through-the-wall in design). These heat pumps often come with variable-speed compressors and blowers,giving them excellent modulation for thermal comfort. These features also contribute to COPs of around 4 for ductless min-split heat pumps. They are also well-suited for ultra-high performance, small-volume homes.

Open drain that carries storm-water runoff from the bottom of a house wall away from the house.