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Hydrated Lime

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

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Hydration

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

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Hydrate

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

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Hydrochlorofluorocarbons (HCFCs)

Hydrochlorofluorocarbons (HCFCs) are potent ozone-depleting compounds. While less destructive than the now-banned chlorofluorocarbons, HCFCs are targeted for gradual phase-out by the US EPA with a total ban going into effect in the year 2030. According to USEPA, the depletion of the Earth’s protective ozone layer is responsible for an increased incidence of skin cancer, cataracts, impairment of human immune systems, and damage to wildlife. https://healthymaterialslab.org/tool-guides/hml-resources

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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.

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Hydrostatic Pressure

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

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Hydronic Heating System

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

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Hydraulic Mortar

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

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Hydronics

The science of cooling and heating water.

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HVAC

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

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Hz

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

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I Joist

A wood joist made of an assembly of laminated veneer wood top and bottom flanges and a web of plywood or oriented strandboard.

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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".

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I-beam

A steel beam with a cross section resembling the letter I It is used for long spans as basement beams or over wide wall openings, such as a double garage door, when wall and roof loads bear down on the opening.

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Hygrometer

An instrument used to measure humidity conditions of the air.

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I-joist

Manufactured structural building component resembling the letter "I". Used as floor joists and rafters. I-joists include two key parts: flangesand webs. The flange of the I joist may be made of laminated veneer lumber or dimensional lumber, usually formed into a 1 ½" width. The webor center of the I-joist is commonly made of plywood or oriented strand board (OSB). Large holes can be cut in the web to accommodate duct work and plumbing waste lines. I-joists are available in lengths up to 60 feet long

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Hydroxide of Lime

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

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Hygroscopic

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

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ICBO

International Conference of Building Officials, a nonprofit organization that publishes the Uniform Building Code.