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ICBO
International Conference of Building Officials.

Ice dam protection membrane
a continuous membrane installed under steep slope roofing materials in areas subject to ice damming that prohibits water which gets through the roof covering from getting into the structure. Must also seal the fasteners that penetrates it.

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.

Ignition temperature
the lowest temperature at which combustion will occur spontaneously under specific conditions.

Impact resistance
resistance to fracture under the sudden application of an exerted force.

Impregnate
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 over the expected service life of the material.

Incline
the slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal units of run. (See Slope.)

Infrared thermography
the process of displaying variations of apparent temperatures (variation of temperature or emissivity or both) over the surface of an object by measuring variations in infrared radiance.

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

Insect screen
wire mesh used to prevent insects from entering the building through ventilators, louvers, or other openings.

Insulation
any of a variety of materials designed to reduce the flow of heat, either from or into a building. (see also Thermal insulation.)

Intake ventilation
the fresh air that is drawn into a passive ventilation system through vents typically installed in the soffit or eave of a roof.

Interlayment
a felt, metal, or membrane sheet material used between courses of steep-slope roofing to improve the weather- and water-shedding characteristics of the primary roof covering during times of wind-driven precipitation. Typically used with wood shakes.

Interlocking shingles
individual shingles that mechanically attach to each other to provide wind resistance without reliance on sealing strips.

Internal Pressure
pressure inside a building that is a function of ventilating equipment, wind velocity, and the number and location of openings and air leaks.

Inverted roof membrane assembly (IRMATM)
a patented, proprietary variation of the "protected membrane roof assembly" in which Styrofoam brand insulation and ballast are placed over the roof membrane. IRMATM and Styrofoam are registered trademarks of the Dow Chemical Company.

IRWC
Institute of Roofing and Waterproofing Consultants

ISANTA
International Staple, Nail & Tool Association.

Isocyanate
a highly reactive organic chemical containing one or more isocyanate (-N=C=0) groups. A basic component in SPF based systems and some polyurethane coating systems.

Isolation sheet
refer to slip sheet.