Architectural and Engineering Glossary

Impact Load

The dynamic effect on a structure,either moving or at rest,of a forcible momentary contact of another moving body.

Impact Noise

Sound generated by impact and carried through a structure;typically, footsteps,the slamming of a door.

Impact Noise Rating (INR)

A rating,expressed by a single number,which is a rough measure of the effectiveness of a floor construction in providing isolation against the noise of impacts;in general,the higher the number,the greater the effectiveness.

Impact Resistance

The resistance of surface (or a material or product) to a shock,such as a hard blow.

Impact Strength, Impact Energy

The amount of energy required to fracture a material; a measure of the material’s resistance to mechanical shock.

Impact Test

A method of determining the resistance of a specimen to fracture upon the application of a dynamic physical shock.

Impact Wrench

A wrench,driven pneumatically or electrically,which produces a series of impulsive torques.


1.The broad transverse band on a door, which stretches from stile to stile and divides the panels horizontally from one another;a door rail.2.The border or framework of a panel of a door.


In painting,the thick laying of pigments. 


In alternating current electric circuits,a quantitative measure of  the opposition to the flow of current upon the application of voltage;measured in ohms.


The rotating member in a pump consisting of a disk with vanes attached to it;moves liquid by accelerating the liquid radially outward.

Impending Slough

The consistency of shotcrete which contains the maximum amount of water that can be used without flow or sag after placement.

Imperfect Arch

A diminished arch.

Imperial Staircase

See double return stair.


Said of a soil whose particles are so closely spaced that the passage of water is either prevented or very slow.


In ceramics,that degree of vitrification evidenced visually by complete resistance to dye penetration;generally signifies zero absorption of water,except for floor and wall tile,which may absorb up to 0.5% water.

Impervious Cover

A ground surface that resists the infiltration of water,thereby resulting in a high rate of water runoff.

Impervious Soil

A fine grained soil,such as clay,having pores too small to permit water to pass except by slow capillary creep.


The span of a building, roof, or arch. 


On drawings,abbr. for “impregnate.” 

Implied Indemnification

An indemnification which is implied by law rather than arising out of a contract.


In ancient Roman dwellings,a cistern set in the atrium or peristyle to receive water from the roofs.

Imposed Load

All loads,exclusive of dead load,that a structure is to sustain.


1.A masonry unit or course,often distinctively profiled, which receives and distributes the thrust at each end of an arch.Also see abutment,springer.2.A vertical member in a gemel or double window taking the place of a mullion;an integral mullion.

Impost Block, Dosseret, Supercapital

A transitional member,often tapered, placed above a column capital to receive the thrust of vaults or arches.

Impregnated Cloth

A cloth impregnated with resin,varnish,shellac,etc.

Impregnated Timber

Timber into which a flame retarder,insect poison,and/or fungicide has been forced under pressure.


The process of adding chemical preservatives,resin,or fire retardants to wood under pressure.Also see Bethell process.

Improved Land

improved land Land which has been provided with water,sewers,sidewalks, and other basic facilities for residential or industrial development.

Improved Wood

Wood impregnated with resin and cured with heat and pressure to increase its strength,durability,and moisture resistance.


A structure or public utility or any other installation or physical change made in a property to increase its value and utility or to improve its appearance.

In Antis

See anta and distyle in antis.

In Cavetto

The reverse of relief,differing from intaglio in that the design is impressed into plaster or clay.

In-and-out Bond

In masonry,a bond, 6 formed by headers and stretchers alternating vertically,esp.when formed at a corner, as by quoins.

In-bank Measure

Measurement of the volume of ground before it has been excavated.


Abbr. for “inch.”

Inactive Leaf, Inactive Door

That leaf of a pair of doors which does not contain a lock,and to which the strike plate is fastened to receive the latch or bolt of the active leaf;usually it is fixed in a closed position by bolts at the top and bottom of the door.


See bark pocket.


In masonry,bonded or forming a bond across the thickness of a wall;composed largely or entirely of headers or bond stones.


1.On drawings, abbr. for “incorporated.”2.On drawings, abbr. for “incoming.”

Inca Architecture

The architecture of the Inca Empire in Peru from the 12th cent.until the Spanish conquest in the 16th cent.,particularly fortified towns with massive stonework.


Abbr. for “incandescent.”


The emission of visible light  as a result of heating.

Incandescent Lamp Base

See lamp base. 

Incandescent Lamp Filament

See filament. 

Incandescent Lighting Fixture

A luminaire,usually complete with incandescent lamp(s), socket(s), reflector, and often with a louver or diffusing medium.

Incandescent Special-service Lamp

One of a class of lamps with special properties to meet particular needs, such as vibration service lamps, rough service lamps, cold service lamps, etc.


Same as encasement.


The hollowed or incised part of an intaglio.

Incense Cedar

A close grained wood having a fragrant resinous odor;highly resistant to moisture.