Glossary

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D

Degree day
A unit that represents a one-degree Fahrenheit deviation from some fixed reference point (usually 65 F) in the mean, daily outdoor temperature. See also heating degree day.
Desiccant
An extremely porous crystalline substance used to absorb moisture from within the sealed air space of an insulating glass unit.
Dewpoint
The temperature at which water vapor in air will condense at a given state of humidity and pressure.
Divided light
A window with a number of smaller panes of glass separated and held in place by muntins.
DOE-2.1E
A building-simulation computer program used to calculate total annual energy use.
Double glazing
In general, two thicknesses of glass separated by an air space within an opening to improve insulation against heat transfer and/or sound transmission. In factory-made double glazing units, the air between the glass sheets is thoroughly dried and the space is sealed airtight, eliminating possible condensation and providing superior insulating properties.
Double-hung window
A window consisting of two sashes operating in a rectangular frame, in which both the upper and lower halves can be slid up and down. A counterbalance mechanism usually holds the sash in place.
Double-strength glass
Sheet glass between 0.115" and 0.133" (33.38 mm) thick.
Drip
A projecting fin or a groove at the outer edge of a sill, soffit, or other projecting member in a wall designed to interrupt the flow of water downward over the wall or inward across the soffit.