Main Vent – Defined under “Plumbing Terms”.

Mansard Roof – Defined under “Roof Types”.

Mantel – The work over a fireplace in front of a chimney, especially a shelf, usually ornamented, above the fireplace.

Masonry – The use of stone, brick or other earthen products for the erection of buildings.

Masonry Types –

Rubble Coursed – Masonry composed of roughly shaped stones laid approximately level and well bonded.

Hollow Masonry Unit – A structural masonry unit, the net bearing area of that is reduced by voids made by mechanical means and is less than 75% solid.

Masonry Veneer – A surface shell or cladding of masonry units attached to a backing not so bonded as to exert a common reaction under load.

Solid Masonry – Masonry composed of units without enclosed spaces between them, well bonded to act as one structural unit.

Solid Masonry Unit – Any structural masonry unit other than a hollow unit and with more than 75% solid.

Matched Joint – In carpentry, a joint made with tongue-and-groove material.

Means of Egress – A doorway, hallway, corridor, exterior passageway or balcony, lobby stair, ramp or other facility or combination thereof, provided for the escape of persons from a building, floor area, contained open space or room to a public thoroughfare or other approved open space. Means of egress include exits and access to all exits. 

Mechanical Equipment – In architectural and engineering practice: all equipment included under the general heading of plumbing, heating, air conditioning, gas fitting and electrical work.

Medullary Rays – Wood tissues that usually run continuously from the pitch to the bark, particularly prominent in quarter-cut oak.

Meeting Rail – The rails of a pair of sash that meet when the sash is closed.

Mesh – Expanded metal or woven wire used as reinforcement for concrete, plaster or stucco.

Metal Lath – Expanded metal or woven wire used to provide a base for plaster or stucco.

Metal Primer – Paint used as a protective and first coat on iron or other metals.

Meter – Defined under “Electrical Terms”.   

Metes and Bounds – A means of describing the location of land by defining boundaries in terms of directions and distance from one or more specific points of reference.

Mezzanine or Mezzanine Floor – An intermediate floor between the floor and ceiling of any storey.

Millwork – Building materials made of finished wood and including such items as inside and outside doors, window and door frames, panel work, mouldings and interior trim. It does not include flooring, ceiling or sliding.

Mineral Aggregate – An aggregate consisting of a mixture of broken stone, broken slag, crushed or uncrushed gravel, sand, stone, screenings and mineral dust.

Mineral Wool – A material used for insulating buildings and produced by sending a blast of steam through molten slag or rock; common types now in use include rock wool, glass wool and slag wool.

Miter Joint – A joint between two pieces of material on a line bisecting the angle of their junction.

Modular Brick – Bricks that are designed for use in walls built in accordance with modular dimensional standards.,

Modular Construction – Construction conforming to a pre-determined measurement unit, e.g. houses are designed with wall lengths in units of four inches, thus making it possible to utilize standard-sized building materials.

Module – A standard unit of measurement in building construction.

Modulus of Elasticity, or Coefficient of Elasticity – The ratio of the unit stress to the unit deformation. It is often called Young’s Modulus.

Modulus of Rupture – The value of unit fiber stress computed on the assumption of linear variation of stress when a beam is ruptured under a known transverse load.

Moisture Barrier – Any material that is used to retard the passage or flow of vapor or moisture into construction and thus prevent condensation.

Moisture Content – The amount of water in a material such as in wood, generally expressed as a percentage of the oven-dry weight of the material.

Monolithic – The term applied to a structure made of a continuous mass of material, e.g. monolithic concrete.

Mortar – A substance produced from prescribed proportions of cementing agents, aggregates and water that gradually sets hard after mixing.

Mortar Bed – Layer of mortar on that any structural member, masonry unit or tile is laid.

Mortise – The cut-out in a board or unit to receive a tenon, lock, hinge, etc.

Moulding – Lumber that has been worked on its side or edge to a uniform cross-section, other than rectangular, to give an ornamental effect.

Mudsill – Timber placed directly on the ground as a foundation for a structure.

Mullion – The perpendicular members that divide the bays or lights of windows or screen-work. See “Window Parts”.

Muntin – A horizontal member that divides lights of glass, windows or doors. See “Windows Parts”.