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Below are terms related to homes and their systems and components. You may encounter these terms in your Home Inspection Report or when communicating with other inspectors or contractors about your home.

M - O

main vent: Principal vent to which branch vents may be connected. Also called a main stack.


mansard roof: A roof that rises by inclined planes from all four sides of a building. The sloping roofs on all four sides have two pitches, with the lower pitch usually very steep and the upper pitch less steep.


mantel: The shelf above a fireplace; also refers to the decorative trim around a fireplace opening.


manufactured (mobile) home: A structure, transportable in one or more sections, which, in the traveling mode, is 8 body-feet or more in width or 40 body-feet or more in length, or which, when erected on site, is 320 or more square feet, and which is built on a permanent chassis and designed to be used as a dwelling with or without a permanent foundation when connected to the required utilities, and includes the plumbing, heating, air-conditioning and electrical systems contained in the structure. This term includes all structures that meet the above requirements except the size requirements and with respect to which the manufacturer voluntarily files a certification and complies with the construction and safety standards. The term does not include any self-propelled recreational vehicle. Calculations used to determine the number of square feet in a structure include the total of square feet for each transportable section comprising the completed structure and based on the structure's exterior dimensions measured at the largest horizontal projections when erected on site. These dimensions include all expandable rooms, cabinets, and other projections containing interior space, but do not include bay windows.


manufactured wood: A building component, such as a truss, beam or joist, that is manufactured using small pieces of wood that are glued or mechanically fastened to form a larger piece (such as GLULAM®, which is glued laminated timber). Often used to create a stronger member that may use less wood. See also oriented strand board (OSB).


masonry: Stone, brick, concrete, hollow-tile, concrete block, gypsum block, and other similar building units and materials, or a combination of the same, bonded together with mortar to form a wall, pier, buttress or similar mass.


masonry primer: An asphalt-based primer used to prepare masonry surfaces for bonding with other asphalt products.


mastic: A heavy-consistency, waterproof compound that is applied to exterior walls and roof surfaces that may remain adhesive and pliable with age.


maximum occupancy load: The maximum number of people permitted in a room measured per foot for each width of exit door. The maximum is 50 per foot of exit.


means of egress: A continuous and unobstructed path out of a building to a public way.


melt point: The temperature at which solid asphalt becomes a liquid.


membrane: A generic term relating to a variety of sheet goods used for certain built-up roofing repairs and applications.


metal edge: Brake metal or a metal extrusion that is secured at the perimeter of a roof to form a weathertight seal.


metal lath: Sheets of metal that are slit and drawn out to form openings and used as a plaster base for walls and ceilings, and as reinforcement over other forms of plaster base.


mezzanine: A semi-permanent, freestanding stair-and-deck system, typically constructed of fiberglass grating, heavy-duty steel and/or aluminum, and installed between two permanent/original floors within an industrial or commercial building in order to provide an open space on and under which can be created informal office areas, storage for inventory, tools and industrial equipment, etc.


Microllam®: Brand name for laminated veneer lumber or LVL (and frequently misspelled as Microlam); a manufactured structural wood beam or other engineered wood product that uses multiple layers or strands of thin wood assembled with adhesives and pressure-treated, giving it a higher strength rating than solid-sawn or milled lumber, and making it less likely to twist, warp, bow or shrink because of its composite nature. Normally comes in l-1/2-inch thickness and 9-inch, 11-1/2-inch and 14-inch widths.


migration: Spreading or creeping of a constituent of a compound onto or into adjacent surfaces. See also bleeding.


mil thickness: Measurement used to determine the thickness of a coating; 1 mil = 0.001 or 1/1000-inch.

millwork: Includes building materials made of finished wood and manufactured in millwork plants and planing mills; examples include interior and exterior doors, doorframes, windows, blinds, porchwork, mantels, panelwork, stairways, moldings, and interior trim. It normally does not include flooring, ceilings or siding.


mineral spirits: A byproduct of petroleum, clear in color, and used as a solvent for asphalt coatings.


mineral stabilizers: Finely-ground limestone, slate, traprock and/or other inert material(s) added to asphalt coatings for durability and increased resistance to fire and weathering.


mineral-surfaced roofing: Asphalt shingles and roll roofing that are covered with granules.


minispread: A smaller variation of a widespread faucet with separate spout and handles designed small enough to fit 4-inch center-to-center faucet holes.


MIP (male iron pipe): Standard threads that are on the outside of a pipe or fitting.


miter (mitre) joint: The joint of two pieces at an angle that bisects the joining angle. For example, the miter joint at the side and head casing at a door opening is made at a 45-degree angle.


mixing valve: A valve that mixes hot and cold water in the valve to obtain a set temperature prior to delivery.


mobile home aluminum roof coating: A durable one-coat application that prolongs the life of mobile home roofs while reflecting the sun's rays and providing a decorative surface; also reduces energy costs.


modified-bitumen roof: A roof covering that is typically composed of a factory-fabricated composite sheet consisting of a copolymer-modified bitumen, often reinforced with polyester and/or fiberglass, and installed in one or more plies. The membrane is commonly surfaced with field-applied coatings, factory-applied granules, or metal foil. The roofing system may incorporate rigid insulation.


moisture content (of wood): Weight of the water contained in wood, usually expressed as a percentage of the weight of the oven-dried wood.


mold: A form of fungus. Some molds can cause disease in humans.


molding (moulding): A wood strip having a coned or projecting surface used for decorative purposes, such as door and window trim.


monitor: A large structure rising above the surrounding roof planes, designed to give light and/or ventilation to the building's interior.


monopost: An adjustable metal column used to support a beam or bearing point, normally made of 11-gauge or Schedule 40 metal, as determined by the structural engineer.


mopping: In roofing, a layer of hot bitumen that is mopped between plies of roofing felt. Full mopping is the application of bitumen in a manner such that the surface is entirely coated with a reasonably uniform coating. Spot-mopping is the procedure of applying hot bitumen in a random fashion of small daubs, as compared to full mopping. Sprinkle mopping is a special application of installing insulation to the decks by dipping a roof mop into hot bitumen and sprinkling the material onto the deck. Strip-mopping is the application of bitumen in parallel bands.


mortar types: Type M, the strongest type, is suitable for general use and is recommended specifically for masonry below grade and in contact with earth, such as foundations, retaining walls and walks. Type S is suitable for general use and is recommended where high resistance to lateral forces is required. Type N is suitable for general use in exposed masonry above grade and is recommended specifically for exterior walls subject to exposure to the elements. Type O is recommended for load-bearing walls of solid units where the compressive stresses do not exceed 100 pounds per square inch, and the masonry wall will not be subjected to freezing and thawing in the presence of excessive moisture.


mud cracks: Cracks that develop from the normal shrinkage of an emulsion coating that has been applied too heavily.


mudsill: A wood foundation member, usually a pressure-treated 2x4 or 2x6, bolted to the foundation and on which other framing members can be attached.


mullion: A vertical bar or divider in the frame between windows, doors and other openings that supports and holds items such as panels, glass, sashes, and sections of a curtain wall.


muntins: Horizontal or vertical bars that divide a sash frame into smaller lites of glass. Muntins are smaller in dimensions and weight than mullions.


muriatic acid: Commonly used as a brick cleaner after masonry work is completed.


mushroom: An unacceptable occurrence when the top of a caisson concrete pier spreads out and hardens to become wider than the foundation wall's thickness.



nailer: A piece of lumber secured to non-nailable decks and walls by bolts or other means, providing a suitable backing onto which roof components may be mechanically fastened.


natural finish: A transparent finish that does not significantly alter the original color or grain of the natural wood. A natural finish is typically achieved using sealers, oils, varnishes, water-repellent preservatives, and other similar materials.


neat plaster: A base coat plaster that does not contain aggregates and is used where the addition of aggregates on the job is desired.


neoprene: A synthetic rubber having physical properties that closely resemble those of natural rubber, and used in weather-resistant products, such as paints, adhesives, gaskets, etc. It is made by polymerizing chloroprenes, which are produced from acetylene and hydrogen chloride.


nesting: A method of re-roofing with new asphalt shingles over old shingles in which the top edge of the new shingles is butted against the bottom edge of the existing shingle tab.


neutral wire: Carries electricity from an outlet back to the service panel; usually color-coded white. See also hot wire and ground.


newel: Any post to which the end of a stair railing or balustrade is fastened.


nipple: A short pipe coupling that is threaded on both ends and installed between fittings.

NM (non-metallic): A flame-retardant type of Romex® cable, which is a non-metallic sheathed cable that contains several conductors. Its use is limited to dry locations.

NMC (non-metallic conduit): A type of Romex® cable, which is a non-metallic sheathed cable that contains several conductors. NMC may be used in damp or corrosive locations, as well as dry areas.


no-cutout shingles: Shingles consisting of a single solid tab with no cutouts.


non-bearing wall: A wall supporting no load other than its own weight.


non-combustible: A substance that does not burn when subjected to fire.


non-drying: A sealant that does not set up or cure. See also butyl. Also called non-curing.


non-fibered aluminum roof coating: Thin but efficient barrier that reflects the sun's harmful rays and prolongs a roof surface's service life. Also used on other metal surfaces.


non-fibered roof and foundation coating: Dual-purpose, thin-viscosity material that doubles as a non-fibered roof and foundation coating.


non-sag: A sealant formulation having a consistency that permits application in vertical joints without appreciable sagging or slumping.


non-veneer panel: Any wood-based panel that does not contain veneer and carries an APA span rating, such as waferboard and oriented strand board.


normal slope application: Method of installing asphalt shingles on roof slopes between 4 inches and 21 inches per foot.


nosing: The projecting edge of a molding or drip usually applied to the projecting molding on the edge of a stair tread.


notch: A crosswise rabbet at the end of a board.



O-ring: Round rubber washer or gasket that is compressed to create a watertight seal, typically in a compression fitting.


OD (outside diameter): A measurement of the diameter of a pipe as taken from the outside edge. A common method for sizing pipe.


offset: A tubular component that permits the offsetting of a drainage run in the same direction.


ogee (OG): A molding with a profile in the form of a letter S; having the outline of a reversed curve.


oil-canning: A term that describes the distortion of thin-gauge metal panels that are fastened in a manner that restricts normal thermal movement.


on center (OC): A term describing the measurement of the distance center to center between like materials, such as studs, rafters, joists, etc. For example, studs placed 16 inches OC are laid out so that there are 16 inches from the center of one stud to the center of the next stud.


open valley: Method of construction by which shingles on both sides of a valley are trimmed along a chalk line snapped on each side of the valley. Shingles do not extend across the valley, leaving the valley flashing exposed.


optimum value engineering (OVE): Framing techniques that reduce unnecessary lumber use and improve the R-value of the wall by reducing thermal bridging and maximizing the wall area that is insulated.


organic: A designation for any chemical compound that contains carbon and hydrogen.


organic felt: An asphalt roofing base material manufactured from cellulose fibers.


OSB (oriented strand board): A manufactured wood panel made of 1- to 2-inch wood chips and glue, often used as a substitute for plywood in exterior walls and roof sheathing. Also called chipboard, flakeboard and waferboard.


outrigger: An extension of a rafter beyond the wall line. Usually, a smaller member is nailed to a larger rafter to form a cornice or roof overhang.


overhang: The part of a roof structure that extends horizontally beyond the vertical plane of the building's exterior walls.


oxidize: The process of something combining with or being exposed to oxygen in the air; rust.

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