Glossary of Roofing and Waterproofing Terms

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Hand-Tabbing: method of spot applying asphalt-based adhesive to shingles for securement and wind resistance.

Hardness: the relative resistance of a material to indentation.

Headlap: the distance of overlap measured from the uppermost ply or course to the point that it laps over the undermost ply or course. (See Figures 14 and 15.)

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Heat Aging: controlled exposure of materials to elevated temperatures over time.

Heat Seaming: the process of joining thermoplastic films, membranes, or sheets by heating and then applying pressure to bring both materials in contact with each other. (See Heat Welding.)

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.

Heat Welding: method of melting and fusing together the overlapping edges of separate sheets or sections of polymer modified bitumen, thermoplastics or some uncured thermoses roofing membranes by the application of heat (in the form of hot air or open flame) and pressure. (See Heat Seaming.)

Hem: the edge created by folding metal back on itself.

Hip: the inclined external angle formed by the intersection of two sloping roof planes. (See Figure 16.)

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Hip Roof: a roof that rises by inclined planes to form one or more hips. (See Figure 17.)

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Hoist: a mechanical lifting device.

Holiday: an area where a liquid-applied material is missing or absent.

Honeycomb: voids left in concrete owing to failure of the mortar to fill effectively the spaces among coarse aggregate particles.

"Hot" or "Hot Stuff": the roofer's term for hot bitumen.

Humidity: the amount of moisture contained in the atmosphere. Generally expressed as percent relative humidity (the ratio of the amount of moisture [water vapor] actually present in the air, compared to the maximum amount that the air could contain at the same temperature.)

HVAC: heating, ventilating, and air conditioning equipment.

Hydration: the chemical reaction by which a substance (such as Portland cement) combines with water, giving off heat to form a crystalline structure in its setting and hardening.

Hydrocarbon: an organic chemical compound primarily containing the elements carbon and hydrogen

Hydrostatic Pressure: the pressure equivalent to that exerted on a surface by a column of water of a given height.

Hydrostatic Pressure Relief System: a system of perimeter and/or under slab drains used to regulate the hydrostatic pressure in the earth surrounding a below-grade structure.

Hygroscopic: the property of a material to attract, absorb, and retain atmospheric moisture.

Hypalon~: a registered trademark of E.l. duPont de Nemours, Inc., for "chlorosulfonated polyethylene" (CSPE). (See Chlorosulfonated Polyethylene.)


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