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Term Definition

A unit of illumination equal to 1 lumen per square meter.

Makeup Air

Air brought into a building from the outside to replace air that has been exhausted.


The property of a metal that permits it to be formed mechanically, such as by rolling or forging, without fracturing.


An access hole in a drainage system to allow inspection, cleaning, and repair.


A metamorphic rock formed largely of calcite, dolomite, or dense limestone.

Masonry Cement

A hydraulic cement used in mortars to increase plasticity and water retention.


Property of a body that resists acceleration and produces the effect of inertia. The weight of a body is the result of the pull of gravity on the body's mass.


The trademarked title of a uniform system for indexing construction specifications published by the Construction Specifications Institute and Construction Specifications Canada.


A doughlike compound available in many different formulations designed for use as sealants and adhesives.

Mat Foundation

A large, single concrete footing equal in area to the area covered by the footprint of the building.

Mechanical Action

The bonding of materials by adhesives that enter the pores and harden, forming a mechanical link.

Mechanical Properties

Properties exhibited by a material's reaction to applied forces, such as tensile strength and compressive strength.


A white crystalline made from calcium cyanamide.

Melting Temperature

The temperature at which a material turns from a solid to a liquid.


A continuous, unbroken roof covering.

Metal Lath

Perforated sheets of thin metal secured to studs that serve as the base for a finished plaster wall.

Metamorpihic Rock

Rock formed by the action of pressure and/or heat on sedimentary soil or rock.

Meter, Electric

A device measuring and recording the amount of electricity passing through it in kilowatt-hours.

Metes and Bounds

A formal description of the boundary lines of a parcel of real property in terms of the length and direction of those lines.

Metric Terms

Metric units shown as equivalents in this Handbook are from the International System of Units in use throughout the world, as established by the General Conference of Weights and Measures in 1960. Their use here complies with the Metric Conversion Act of 1975, which committed the United States to a coordinated voluntary conversion to the metric system of measurement. Refer to the Appendix for metric units and conversion factors applicable to subjects covered in this Handbook. For additional information, refer to ASTM E380-76, Standard for Metric Practice.

Mild Steel

Steel containing less than 0.3 percent carbon.


An agent that helps prevent the growth of mold and mildew on painted surfaces.


Wood interior finish items manufactured in a factory, such as doors, windows, and cabinets.


Joint formed by two pieces of material cut to meet at an angle.

Model Code

Building code, written and published by a building-official association, available to states, counties and municipalities for adoption (for a fee) in lieu of their own, e.g., Uniform Building Code, Standard Building Code, National Building Code.

Modified Bitumens

A roofing membrane composed of a polyester or fiberglass mat saturated with a polymer-modified asphalt.

Modular Size

A dimension that conforms to a given module, such as the 48-inch width of plywood panels.


(1) In architecture, a selected unit of measure used as a basis for building layout; (2) In industrialized housing, a three-dimensional section of a building, factory-built, shipped as a unit and interconnected with other modules to form the complete building. Single-family units factory-built in two halves are usually referred to as "sectionals."

Modulus of Elasticity (E)

Ratio between deformation, a measure of the stiffness of a material.

Modulus of Rupture

A measure of the ultimate load-carrying capacity of a structural member.

Moisture Barrier

A membrane used to block the passage of water, and water vapor through an assembly of materials, suh as a wall.

Moisture Content

The amount of water contained in wood expressed as a percentage of the weight of the wet wood to the weight of an oven-dry sample.


The tendency of a force to cause rotation about a give point or axis.

Moment of Inertia (I)

Calculated numerical relationship (expressed in in.4) of the resistance to bending of a member, a function of the cross-sectional shape and size. A measure of the stiffness of a member based on its shape. Larger moments of inertia indicate greater resistance to bending for a given material.

Monolythic Concrete

Concrete cast with no joints except construction joints: a continuous pour.


An organic molecule that can be converted into a polymer by chemical reaction with similar molecules or organic molecules.


A plastic mixture of cementitious materials, water, and fine aggregate.

Mortar Flow

A measure of the consistency of freshly mixed mortar related to the diameter of a molded truncated cone specimen after the sample has been vibrated a specified number of times.


A decoration made up of small pieces of inlaid stone, glass, or tile.

Motor Control

A device that governs the electric power delivered to one or more electric motors.

Motor Control Center

Controllers used to start and stop electric motors and protect them from overloads.

Moulding (also Molding)

Narrow decorative strip applied to a surface.

Moving Ramp

A conveyor belt system used to move people or packages up or down an incline.

Moving Walk

A conveyor belt system operating at floor level used to move people in a horizontal direction.


Vertical bar or division in a window frame separating two or more panes.

Multiple Dwelling

A building containing three or more dwelling units.


Horizontal bar or division in a window frame separating multiple panes or lights.

Music/Machinery Transmission Class (MTC)

Rating developed by U.S. Gypsum Company to isolate music and machinery/mechanical equipment noise or any sound with a substantial portion of low frequency energy. MTC does not replace Sound Transmission Class (STC) but complements it.

Nail Pop

The protrusion of the nail usually attributed to the shrinkage of or use of improperly cured wood framing.

Nail Popping

The loosening of nails holding gypsum board to a wall or ceiling. It produces a bulge in the surface of the gypsum panel.

Natural Fibers

Fibers found in nature, such as wool and cotton.


National Board of Fire Underwriters, now merged into the American Insurance Assn.


National Bureau of Standards, a federal agency.


National Conference of States on Building Codes and Standards, a nonprofit organization formed to increase interstate cooperation and coordinate intergovernmental reforms of building codes.

Neat Plaster

A gypsum plaster with no aggregates or fillers added. Sometimes called unfibered gypsum.

Needle Beam

A steel or wood beam that is run through an opening in a bearing wall and used to support the wall and related loads as work on the foundation below the wall is performed.

Neutral Axis

The plane through a member (at the geometric center of the section in symmetrical members) where the fibers are neither under tensile nor compressive stress.


National Fire Protection Assn., an international technical society that disseminates fire prevention, fighting and protection information. NFiPA technical standards include the National Electrical Code which is widely adopted.


National Forest Products Association.

Noise Reduction Coefficient (NRC)

A single number indicated by the amount of airborne sound energy absorbed into a material. The arithmetic average of sound absorption coefficients at 250, 500, 1000 and 2000 Hz.


Term indicating that the full measurement is not used; usually slightly less than the full net measurement, as with 2" x 4" studs that have an actual size when dry of 1&1/2" x 3&1/2".

Non-Conforming Use

A particular use of land or a structure which is in violation of the applicable zoning code. Generally, if the use was established prior to the code rule which it contravenes, it may continue to exist.


Refers to a structural part that does not carry a load.

Noncalcerous Clays

Clays containing silicate of alumina, feldspar, and iron oxide.


Definition excerpted from the ICBO Uniform Building Code: 1. Material of which no part will ignite and burn when subjected to fire. 2. Material having a structural base of noncombustible material as defined, with a surface not over 1/8" thick that has a flame spread rating of 50 or less. The term does not apply to surface finish materials.

Nondestructive Testing

Methods of testing an item that do not destroy the item being tested.


Metallic materials in which iron is not a principal element.

Nonheat-Treatable Alloys

Alloys that do not increase in strength when they are heat treated but that do gain strength by the addition of alloying elements.

Nonprestressed Units

Concrete structural members in which the reinforcing steel is not subject to prestressing or post-tensioning.


A synthetic plastic made from coal, tar, and water.


A caulking material made from hemp fibers treated with tar.


Interval between two sounds having a basic frequency ratio of two. The formula is 2n times the frequency, where n is the desired octave interval. The octave band frequency given in sound test results is usually the band center frequency, thus the 1000 Hz octave band encompasses frequencies from 707 Hz to 1414 Hz (n = ± 1/2). The 1000 Hz one-third-octave band encompasses frequencies from 891 Hz to 1122 Hz (n = ± 1/6).

Oil-Based Paint

Paint composed of resins requiring solvent for reduction purposes.

Opaque Coatings

Coatings that completely obscure the color and much of the texture of the substrate.

Open Drainage

The removal of unwanted water by means of surface devices.

Open-Web Joist

A prefabricated steel truss made of welded members, used for floor and roof construction.

Organic Material

A class of compounds comprising only those existing in plants and animals.

Oriented Strand Board

A panel made from wood strands that have their strand face oriented in the long direction of the panel.

Outlet Box

A box that is part of the electrical wiring system that contains one or more receptacles.

Overlaid Plywood

Plywood panels whose exterior surfaces are covered with a resin-impregnated fiber ply.


The operation of electrical equipment in excess of the normal full-loaded electrical rating or of a conductor carrying current in excess of its rated capacity.


A reaction between a material and oxygen in the atmosphere.

Oxide Layer

In aluminum, a very thin protective layer formed naturally on aluminum due to its reaction to oxygen.


To convert an element into oxide, such as rusting steel.


An approximately level building area.


A metal form used to form the cavities between joists in cast-in-place concrete floors and roofs.


A panel that includes fuses or circuit breakers used to protect the circuits in a building from overloads.

Panelized Construction

Construction that uses preassembled panels for walls, floors, and roof.

Parallel Strand Lumber

Lumber made from lengths of wood veneer bonded to produce a solid member.

Parapet Wall

Extension of an exterior wall above and/or through the roof surface.


The application of a portland cement plaster on masonry and concrete walls to make them less permeable to water.


A sheet product manufactured from wood particles and a synthetic resin or other binder.


A non-load-bearing interior wall.

Party Wall

A wall built on the dividing line between two adjoining parcels, in which each owner has an equal share of ownership.

Passive Solar System

A heating or cooling system that collects and moves solar heat whiout using mechanical power.


A thin brick used as the finished floor covering.

Penny (d)

Suffix designating the size of nails, such as 6d (penny) nail, originally indicating the price, in English pence, per 100 nails. Does not designate a constant length or size, and will vary by type (e.g., common and box nails).

Performance Specification

States how a building element must perform as opposed to describing equipment, products or systems by name.


A lightweight material made from volcanic rock.


A unit of measurement of Water Vapor Permenance (ASTM).

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