"H" section—A steel member with an H cross section. (See also, structural steel members, wide flange and standard shapes).

Half-life—The time required for an unstable element to lose one-half of its radioactive intensity.

Haunch—The deepened portion of a column or rafter, designed to accommodate the higher bending moments at such points. (Usually occurs at connection of column and rafter.)

Header—A horizontal framing structural member of a door, window, or other framed opening.

Headlap—The minimum distances measured at 90 degrees to the eave along the face of a shingle or felt as applied to a roof, from the upper edge of the shingle or felt, to the nearest exposed surface.

Heat capacity—The amount of energy required to raise the temperature of a substance a given increment.

Heat seaming—The process of joining two or more thermoplastic films or sheets by heating areas in contact with each other to the temperature at which fusion occurs. The process is usually aided by a controlled pressure. In dielectric seaming, the heat is induced within films by means of radio frequency waves.

Heat transfer—The transmission of thermal energy from a location of higher temperature to a location of lower temperature. This can occur by conduction, convection or radiation.

High speed neutron—High velocity neutrons such as would emanate directly from atomic nuclei such as the radioactive isotopes used in roof moisture meters. (See Thermalization).

High strength bolts—A type of hardened steel bolt used to join structural members by clamping action.

High strength steel—Structural steel having a yield strength in excess of 36,000 pounds per square inch (250 MPa).

Hinged base—See Pin connection.

Hip roof—A roof which rises by inclined planes from all four sides on the building. The line where two adjacent sloping sides of a roof meet is called the Hip.

Histogram—A chart showing a distribution of data, e.g., the number of occurrences of a value plotted versus the value itself. Sometimes called a bar chart.

Holiday—An area where a liquid applied material is missing.

Homopolymer—A natural or synthetic high polymer derived from a single monomer.

Hot dip metallic coating—Adherent protective coating applied by immersing steel in a molten bath of coating material.

"Hot stuff11" or "hot11"—A roofer's term for hot bitumen.

Hot-rolled shapes—Steel sections (angles, channels, I-beams, etc.) which are formed while in a semi-molten state at the steel mill to a shape having standard dimensions and properties specified by AISC or the steel producer.

Humidity—The amount of moisture contained in the atmosphere. Generally expressed percent relative humidity. (The ratio of the vapor pressure to the saturation pressure for given conditions times 100.)

Humidity test—A test involving exposure of specimens at controlled levels of humidity and temperature.

Hybrid vision—A superimposition of thermal data on a visible field to provide clarity.

Hydrocarbons—An organic chemical compound containing mainly the elements carbon and hydrogen. Aliphatic hydrocarbons are straight chain compounds of carbon and hydrogen. Aromatic hydrocarbons are carbon hydrogen compounds based on the cyclic or benzene ring. They may be gaseous (CH4, ethylene, butadiene), liquid (hexene, benzene), or solid (natural rubber, napthalene, cis-polybutadiene).

Hygroscopic—Attracting, absorbing, and retaining atmospheric moisture