Glossary

Construction Dictionary and Glossary of Construction Terms

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H

Term	Definition
Heat	Form of energy thought to be characterized by the rate of vibration of the molecules of a substance. The hotter the substance, the faster the molecules vibrate. On the other hand, when there is no heat present it is thought the molecules will be at rest, which theoretically occurs at absolute zero, -459.7°F (-273.15°C or 0.0°K).
Heat Quantity (Btu)	Common unit of measure of the quantity of heat is the British Thermal Unit (Btu). One Btu is the amount of heat required to raise one pound of water from 63° to 64°F (1 Btu = 1055.06 J). This is about the amount of heat given off by one wooden match. A pound of coal can produce 13,000 Btu.
Heat Transfer	Heat always flows toward a substance of lower temperature until the temperatures of the two substances equalize. It travels by one or more of three methods: conduction, convection or radiation.
Heel of Rafter	Seat cut in a rafter that rests on the wall plate.
Hertz	The units of measure of sound frequency, named for Heinrich H. Hertz. One Hertz equals one cycle per second.
Honeycomb	Any substance having cells suggesting a mass of cells such as those built by the honeybee. Some hollow-core doors use the honeycomb principle in their construction.
HUD	Housing and Urban Development, federal agency.
HUD Mobile Home Standards	Officially, the National Mobile Home Construction and Safety Standards Act of 1974 for construction of mobile homes. Includes the following agencies: DAPIA Design Approval Primary Inspection Agency and IPIA Production Inspection Primary Inspection Agency.
HVAC	Heating, ventilating and air conditioning. (ASHRAE Guide is the technical reference source.)
Hygrometric Expansion	All materials, particularly those of organic origin, expand and contract in relation to their moisture content, which varies with environment. The Hygrometric Coefficient of Expansion is expressed in "Inches Per Inch Per Percent Of Relative Humidity." Example: gypsum board has a coefficient of 7.2 x 10-6 in. per in. per %rh. This means that with an increase in relative humidity of from 10% to 50%, a gypsum board wall 300 ft. long will have an unrestrained linear expansion of 1.0368" or 1&1/32".