Roofing Terms that Start with the Letter “I”

Roof Online’s Glossary of Roofing Terms

By Roof Online Staff • Updated October 8, 2022

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I-Beam: A structural steel beam with a cross section resembling the letter I.

IBC: International Building Code. Model building code developed by the International Code Council and adopted, often with local amendments, by most jurisdictions in the United States.

IBHS: Insurance Institute for Business & Home Safety

ICAA: Insulation Contractors Association of America

ICBO: International Conference of Building Officials, former publisher of the Uniform Building Code. One of the three founding organizations of the International Code Council.

ICC: International Code Council. Publisher of the International Building Code.

Ice and Water Shield: A self-adhered rubberized asphalt underlayment typically applied on sloped roofs under mechanically-fastened roof coverings such as asphalt shingles, tile, or standing seam metal due to its ability to remain watertight when penetrated by fasteners such as roofing nails. “Grace Ice & Water Shield” was and is a trade name, but “Ice and Water Shield” has become genericized and is used to indicate any similar waterproofing membrane. 

Ice Dam: A build-up of ice at the overhanging eaves of a sloped roof where the roof’s surface transitions from warm to cold.  Due to the melting and re-freezing of snow and ice on the overhang, the ice accumulates, blocks drainage, and can force water back up under the shingles, causing leaks.

Ice Guard: Or snow guard. A device installed on a roof to prevent snow or ice from falling and hurting people, plants, or objects below.

Ignition Temperature: The minimum temperature to which a material must be heated for it to spontaneously ignite without an external ignition source such as a flame.

IIPLR: The Insurance Institute for Property Loss Reduction (now the Insurance Institute for Business & Home Safety).

Imbricate: Overlapping in a regular fashion, as with shingles or tiles.

Impact: A force or shock applied over a short period of time when two bodies collide.

Impact Load: A dynamic structural load on a building caused by an impact.

Impact Resistance: The resistance of a roofing material to a shock, such as from the impact of hail or foot traffic; the ability to resist damage from such a shock.

Impermeable: Not allowing water to pass through.

Impervious: Impermeable.

Imposed Load: All loads, except dead load, that are to be sustained by a structure.

Impregnate: To saturate and coat the fibers of (roofing felts, reinforcement mats, fabrics, etc.).

Inclination: The angle formed by a line or a surface by its intersection with the horizontal, the vertical, or another line or surface.

Incline: The steepness of a roof expressed as a ratio of vertical change to horizontal change such as rise/run or as a percentage (where 12/12 = 100%).

Indoor Air Quality (IAQ): a term that refers to the composition of the air inside and around buildings as it relates to the health and comfort of the occupants. ASHRAE Standard 62.1 defines acceptable IAQ as “Air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction.”

Infrared: Infrared radiation is electromagnetic radiation with longer wavelengths than those of visible light. Most thermal radiation emitted by objects near room temperature is infrared.

Infrared Thermography: Also thermal imaging. The use of an infrared camera to detect infrared radiation and produce images of that radiation. The amount of radiation given off by an object increases with temperature, so infrared thermography allows the detection of differences in temperature. Infrared cameras are typically used in non-destructive roof moisture surveys to identify wet areas of roof insulation, as wet insulation retains heat longer than dry insulation after the sun goes down.

Inorganic: Not composed of organic life nor the products of organic life (such as wood or cellulose); relating to compounds not containing hydrocarbon groups.

Insect Screen: A material, such as wire mesh, used to keep insects from entering a building through vents or other openings.

Inset Dormer: Also Recessed Dormer. A dormer which is partially set back from the surface of a sloped roof rather than projecting entirely beyond the sloped roof surface.

Insulating Concrete: Concrete with low thermal conductivity.

Insulation: (Thermal insulation.) Material used to help maintain a desired temperature by reducing the flow of heat.

Intake: An opening designed to allow the entry of air into an HVAC system.

Intake Ventilation: The elements of a ventilation system used to bring fresh air into a building. In a passive ventilation system, these are usually vents installed in the soffit or eaves of a building.

Integral Waterproofing: The improvement of the ability of concrete to resist water absorption by the addition of a admixture during the mixing of the concrete.

Interlaminar Adhesion: Refers to the adhesive bond between passes, or layers, of sprayed polyurethane foam.

Interlayment: A waterproofing material, such as roofing felt or sheet membrane, installed between adjacent courses of a steep-slope roof covering such as wood shakes to improve the roof’s waterproofing ability during periods of wind-driven rain or snow.

Interlocking Shingles: Individual shingles designed to mechanically attach to each other to improve the wind resistance of the roof covering. Also see T-Lock Shingles.

Intermediate Rafter: See Common Rafter.

Internal Pressure: Atmospheric pressure inside a building which is a function of external wind-speed, the ventilation system, and the number and location of openings in the building envelope.

International System of Units: Abbreviated “SI” for “Système International D’unités”. The metric system.

Intersecting Gable: See Cross Gable.

Interstitial Condensation: Also Concealed Condensation. Water vapor condensation within a building element, as within a roof assembly.

Intumescent: Describes a substance that swells up (increases in volume) as a result of heat exposure. Intumescent coatings are typically used in passive fire protection systems.

Inverted Roof Membrane Assembly (IRMA®): A type of protected membrane roof assembly in which Styrofoam® brand extruded polystyrene insulation is used. IRMA® and Styrofoam® are registered trademarks of the Dow Chemical Company.

IR: Abbreviation for “inside radius”.

IR: Abbreviation for “infrared”.

Irregular Pitch: Describes a roof with a slope that is not constant.

IRWC: Institute of Roofing and Waterproofing Consultants.

ISANTA: International Staple, Nail, and Tool Association.

ISO: The International Organization for Standardization. “ISO” is not an acronym; rather, it’s a standardized short form of the name.

Iso: Also polyiso. Short for polyisocyanurate insulation.

Iso Board: Short for polyisocyanurate board insulation.

Isocyanate: Isocyanates are a family of highly reactive, low molecular weight chemicals. They are widely used in the manufacture of flexible and rigid foams, fibers, coatings such as paints and varnishes, and elastomers, and in the production of building insulation materials. They are a basic component of sprayed polyurethane foam.

Isolator: See Vibration Isolator.

Italian Roof: See “Hip Roof”.

Italian Tile: Mission tile.