Exterior wall of a building that is supported by the structure and carries no part of the vertical load except its own. Curtain walls must be designed to withstand wind loads and transfer them to the structure.

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Cycle (Acoustic)

One full repetition of a motion sequence during periodic vibration. Movement from zero to +1 back to zero to -1 back to zero. Frequency of vibration is expressed in Hertz (cycles per second -- see Frequency).

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Dado

A groove cut into a board or panel intended to receive the edge of a connecting board or panel.

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Decibel (dB)

A unit for measuring sound energy or power. Adopted for convenience in representing vastly different sound pressures.

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Daylight

The end of a pipe (the terminal end) that is not attached to anything.

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Damper

A metal "door" placed within the fireplace chimney. Normally closed when the fireplace is not in use. A movable vane used to vary the volume of air passing through a duct, inlet, or outlet.

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Deciduous

Describing trees that shed their leaves annually, as opposed to evergreen.

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Dead Load

Load on a building element contributed by the weight of the building materials.

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Dead bolt

An exterior security lock installed on exterior entry doors that can be activated only with a key or thumb-turn. Unlike a latch, which has a beveled tongue, dead bolts have square ends.