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Term Definition
Hachure

A shading technique used to depict ground form.

Hardboard

A general term used to describe a panel made from interfelted lignocellulose fibers consolidated under heat and pressure.

Hardness

A measure of the ability of a material to resist indention or surface scratching.

Hardwood

A botanical group of trees that have broad leaves that are shed in the winter (it does not refer to the hardness of the wood).

Hardwood Plywood

Plywood with various species of hardwoods used on the outer veneers.

Haunch

A projection used to support a member, such as a beam.

Header Joist

A structural member fastened between two parallel full-length framing members to support cut off members at the openings.

Heartwood

The wood extending from the pith to the sapwood.

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 Exchanger

A device to transfer heat between two physically separated fluids.

Heat Loss

The energy needed to warm outside air leaking into a building through cracks around doors, windows, and other places.

Heat Pump

A heating/refrigerating system in which heat is taken from a heat source, such as the air, and given up to the space to be heated. For cooling, it takes heat from the air in the space and gives it up outdoors.

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.

Heat Treating

Heating and cooling a solid metal to produce changes in physical and mechanical properties.

Heat-Strengthened Glass

Glass that has been strengthened by heat treatment.

Heat-Treatable Alloys

Aluminum alloys whose strength characteristics can be improved by heat treatment.

Heating Value

The amount of heat produced by the complete combustion of a unit quantity of fuel.

Heavy Timber Construction

A type of wood-frame construction using heavy timbers for the columns, beams, joists, and rafters.

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.

Hiding Power

The ability of a paint to hide the previous color or substrate.

Hinge Joint

A joint that permits some action similar to a hinge and in which there is no appreciable separation of the joining members.

Hip Roof

A roof consisting of four sloping planes that intersect forming a pyramidal shape.

Hoistway, Elevator

A fire-resistant vertical shaft in which the elevator moves.

Hollow Brick

A clay masonry unit whose net cross sectional area in the plane of the bearing surface is not less than 60 percent of the gross cross sectional area of that face.

Hollow Clay Masonry

A unit whose core area is 25 to 40 percent of the gross cross-sectional area of the unit.

Hollow Concrete Masonry

Concrete masonry units that have open cores.

Hollow-Core Door

A door with face veneers on the outer surfaces, wood spacers around the edges, and a hollow interior supported with a honey-comb grid.

Holow-Core Slab

A precast concrete structural slab that uses internal cavities to reduce its weight.

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.

Horizontal Sheer

The tendency of the top wood fibers to move horizontally in relationship to the bottom fibers.

Hot Melt

Adhesives that bond when they are heated to a liquid form.

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.

Humidifier

A device used to add moisture to the air.

Humidity

The amount of water vapor withing a given space.

Humidity

The amount or degree of moisture in the air.

HVAC

Heating, ventilating and air conditioning (ASHRAE Guide is the technical reference source).

Hydrate

The capacity of lime to soak up water serveral times its weight.

Hydrated Lime

Calcium hydroxide made by burning calcium carbonate, which forms caclium oxide that can then chemically combine with water.

Hydration

A chemical reaction between water and cement that produces heat and causes the cement to cure or harden.

Hydraulic Elevator

An elevator having the car mounted on top of a hydraulic piston that is moved by the action of hydraulic oil under pressure.

Hydraulic Mortar

A mortar that is capable of setting and hardening under water.

Hydronic Heating System

A system that circulates hot water through a system of pipes and convectors to heat a building.

Hydronics

The science of cooling and heating water.

Hydrostatic Pressure

The pressure equivalent to that exerted on a surface by a column of water of a specified height.

Hydroxide of Lime

The product produced by the chemical reaction during the slaking or hydrating of lime.

Hygrometer

An instrument used to measure humidity conditions of the air.

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".

Hygroscopic

The ability to readily absorb and retain moisture from the air.

Hz

The abbreviation for hertz, the unit of measurement of the frequency of electric current. It represents the number of cycles per second.