Joist: any of the small timbers, metal or wood beams arranged parallel from wall to wall to support a floor, ceiling, or roof of a building.

Kesternich Test: simulates acid rain conditions by subjecting test specimens to a sulfur dioxide atmosphere as well as condensing moisture for the purpose of evaluating rust/corrosion characteristics.

Knee Cap: a metal cover trim that fits over a panel rib after it has been cut and bent.

Lap: that part of a roofing, waterproofing, or flashing component that overlaps or covers any portion of the same or another type of adjacent component.

Lap Cement: an asphalt-based roof cement formulated to adhere overlapping plies or asphalt roll roofing.

Lap Seam: occurs where overlapping materials are seamed, sealed, or otherwise bonded.

Latex: a colloidal dispersion of a polymer or elastomer in water which coagulates into a film upon evaporation of the water.

Lead: a soft workable metal used for miscellaneous flashings.

Leader Head: see Conductor Head.

Leeward: the opposite direction from which the wind is blowing. The side sheltered from the wind.

Life Cycling Costing: a method of economic analysis that takes into account expected costs over the useful life of an asset.

Lift: the sprayed polyurethane foam that results from a pass. It usually is associated with a certain pass thick-ness and has a bottom layer, center mass, and top skin in its makeup.

Live Loads: temporary loads that the roof structure must be designed to support, as required by governing building codes. Live loads are generally moving and/or dynamic or environmental, (e.g., people, installation equipment, wind, snow, ice or rain, etc.).

Loose-laid Membranes: membranes that are not attached to the substrate except at the perimeter of the roof and at penetrations. Typically, loose-laid membranes are held in place with ballast, such as water-worn stone, gravel, pavers, etc.

Photo Example

Mansard: a decorative steep-sloped roof on the perimeter of a building.

Mansard Roof: a steeper roof that terminates into a flat roof at its high point.

Material Safety Data Sheets (MSDS): a written description of the chemicals in a product, and pertinent other data including such things as safe handling and emergency procedures. In accordance with OSHA regulations, it is the manufacturer's responsibility to produce an MSDS and the employer's responsibility to communicate its contents to employees.

Mechanically-Fastened Membranes: generally used to describe membranes that have been attached at defined intervals to the substrate. Mechanical fastening may be performed with various fasteners and/or other mechanical devices, such as plates or battens.

Membrane: a flexible or semi-flexible material, which functions as the waterproofing component in a roofing or waterproofing assembly, and whose primary function is the exclusion of water.

Metal Flashing: accessory components fabricated from sheet metal and used to weatherproof terminating roof covering edges. Frequently used as through-wall flashing, cap flashing (coping), counterflashing, step-flashing, etc. (See Flashing.)

Mil: a unit of measure, one mil is equal to 0.001 inches or 25.400 microns, often used to indicate the thickness of a roofing membrane.

Mineral Fiber: inorganic fibers of glass, asbestos, or rock (mineral wool).

Mineral-Surfaced Roofing: roofing materials whose surface or top layer consists of mineral granules.

Modified Bitumen: (1) a bitumen modified through the inclusion of one or more polymers (e.g., atactic polypropylene, styrene butadiene styrene, etc.); (2) composite sheets consisting of a polymer modified bitumen often reinforced and sometimes surfaced with various types of mats, films, foils, and mineral granules.

Moisture Relief Vent: a venting device installed through the roofing membrane to relieve moisture vapor pres-sure from within the roofing system.

Moisture Scan: the use of a mechanical device (capitance, infrared, or nuclear) to detect the presence of moisture within a roof assembly. (See Non-Destructive Testing.)

Mole Run: a meandering buckle or ridging in a roof membrane not associated with insulation or deck joints.

Mop-and-Flop: an application procedure in which roofing elements (insulation boards, felt plies, cap sheets, etc.) are initially placed upside down adjacent to their ultimate locations, are coated with adhesive or bitumen, and are then turned over and applied to the substrate.

Mopping: the application of hot bitumen, with a roofer's hand mop or mechanical applicator, to the substrate or to the felts of a bituminous membrane.

Solid Mopping: a continuous mopping of a surface.
Spot Mopping: a mopping pattern in which hot bitumen is applied in roughly circular areas, leaving a grid of unmopped, perpendicular bands on the roof.
Sprinkle Mopping: a random mopping pattern in which heated bitumen beads are strewn onto the substrate with a brush or mop.
Strip Mopping: a mopping pattern in which hot bitumen is applied in parallel bands.

Mud Cracking: surface cracking of a material whereby the degraded material appears similar to dried, cracked earthen mud.