Term Description
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

A method of melting and fusing together the overlapping edges of separate sheets or sections of polymer-modified bitumen, thermoplastics or some uncured thermoset roof and waterproofing membranes by the application of heat (in the form of hot air or open flame) and pressure.


To be installed by heating the underside of the sheet with a propane torch or other heating device, melting the polymer-modified bitumen on the bottom side and adhering the sheet in the molten material.


The edge created by folding metal back on itself.


The sloping line along the outer angle formed by the meeting of two sloping sides of a roof with eaves that meet at a right angle.

Hip roof

A roof that rises by inclined planes from all four sides of a building to form hips at the intersection of adjacent roof slopes.


A cover, usually of light-gauge metal, over piping or other rooftop equipment.

Hot-liquid-applied polymer-modified asphalt

A waterproofing membrane consisting of a blend of asphalt, styrene butadiene styrene (SBS) rubber polymer and mineral stabilizer, used with or without reinforcing sheets.


The condition of the atmosphere with respect to water vapor. See "relative humidity."


Heating, ventilating and air-conditioning.


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.


An organic chemical compound primarily containing the elements carbon and hydrogen. Hydrocarbons are divided into two general classes—aliphatic and aromatic—differentiated by the type of carbon-carbon bonds they contain. Aliphatic hydrocarbons are straight chain compounds. Aromatic hydrocarbons contain one or more benzene ring or naphthalene ring structure.

Hydrostatic pressure

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


Attracting, absorbing and retaining atmospheric moisture.


A registered trademark of E.I. du Pont de Nemours & Co. for chlorosulfonated polyethylene (CSPE). See "chlorosulfonated polyethylene."


International Building Code. A model building code published by the International Code Council; applies to all construction except detached one- and two-family dwellings and townhouses.


Insurance Institute for Business and Home Safety. IBHS is an association of property insurance companies.


International Code Council. A nonprofit organization dedicated to developing and maintaining a single set of comprehensive, coordinated national building codes (I-Codes®); established in 1994 by three major U.S. model building code bodies: Building Officials and Code Administrators International Inc., International Conference of Building Officials and Southern Building Code Congress International Inc.

Ice dam

A mass of ice formed at the transition from a warm to a cold roof surface, frequently formed by refreezing meltwater at the overhang of a steep roof causing ice and water to back up under roofing materials.

Impact resistance

Resistance to fracture under the sudden application of an exerted force.


In roofing materials manufacture, to completely surround the fibers in a felt or mat with bitumen with the spaces between the fibers partially or completely filled without a continuous coating of bitumen on the surface.

In-service R-value

Thermal resistance value established under installed conditions and measured during the expected service life of the material.


The slope of a roof expressed in percent or in units of vertical rise per units of horizontal run.


Being or composed of materials other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin.


Any of a variety of materials designed to reduce the flow of heat from or into a building. See "thermal insulation."