Glossary of Roofing Terms

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.

k-Factor: thermal conductivity for a unit thickness of material. Expressed at Btu~ln/Hr.Ft2~°F. R-value is equal to the thickness of the thermal material divided by the k-factor (R=x/k where x = thickness).

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

Laminate: to bond two or more layers of a material together to make a finished product.

Laminated Shingles: see Dimensional Shingles or Architectural Shingles.

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.

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

Light Reflectance: the percentage of light that is not absorbed by the surface of a material.

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.).

Load Deflection: see Deflection.

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.

Low Temperature Flexibility: the ability of a membrane or other material to remain flexible (resist cracking when flexed), after it has been cooled to a low temperature.

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. (See Figure 18.)

Masonry: anything constructed of such materials as bricks, stone, concrete blocks, ceramic blocks, or concrete.

Mastic: see Asphalt Roof Cement.

Mat: a thin layer of woven, non-woven, or knitted fiber that serves as reinforcement to the material or membrane.

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 Film: a layer of foil made from a single metallic substance, or from an alloy, that is laminated to a membrane during manufacture. The metal foil serves as the weathering surface of the membrane or flashing material.

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, stepflashing, etc. (See Flashing.)

Metallic Waterproofing: a compound modified through the inclusion of one or more polymers (e.g. atactic polypropylene, styrene butadiene sytrene, 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.

Meter: unit of length measurement in the metric system, equal to 39.37 inches.

Mica Dust: crystallized complex silicate minerals that are pulverized into dust form for use as a release agent. (See Talc.)

Migration: the absorption of oil or vehicle from a compound into an adjacent porous surface.

Mill: 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.

Mildew: a superficial coating or discoloring of an organic material due to fungal growth, especially under damp conditions.

Millimeter: a unit of measure equal to one thousandth (0.001) of a meter, or 0.03937 inches.

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

Mineral Granules: see Granules.

Mineral Stabilizer: a fine, water-insoluble inorganic material, used in a mixture with solid or semi-solid hit'~minous materials.

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

Mineral-Surfaced Sheet: a roofing sheet that is coated on one or both sides with asphalt and surfaced with mineral granules.

Miter: the joint produced by joining two diagonally cut pieces.

Model Codes: a compilation of standards or codes established to provide uniformity in regulations pertaining to building construction. Examples: ICBO - International Conference of Building Officials; BOCA - Building Officials and Code Administrators; SBC - Standard Building Code.

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 Contour Map: a map used to graphically define the location of moisture within a roof assembly after a moisture scan has been performed.

Moisture Relief Vent: a venting device installed through the roofing membrane to relieve moisture vapor pressure 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.

Monolithic: formed from or composed of a single material; seamless.

Monomer: a simple molecule that is capable of combining with a number of like or unlike molecules to form a polymer.

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 unmapped, 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.

Multiple Coat: two or more layers of coating applied to a substrate.

Nailer: (commonly referred to as Blocking) a piece or pieces of dimensional lumber and/or plywood secured to the structural deck or walls, which provide a receiving medium for the fasteners used to attach membrane or flashing. Generally, it is recommended that nailers be the same thickness as the adjacent insulation, and may be treated with a non-oil-borne preservative, and be of sufficient width to fully support the horizontal flashing flange of a metal flashing (where used).

Nailing: the application of nails. May be: (1) exposed nailing of roofing wherein nail heads are exposed to the weather; (2) concealed nailing of roofing wherein nail heads are concealed from the weather by an overlapping material.

Negative Side Waterproofing: an application wherein the waterproofing system and the source of hydrostatic pressure are on opposite sides of the structural element.

Neoprene: a synthetic rubber (polychloroprene) used in liquid-applied and sheet-applied elastomeric roof membranes or flashings.

Nesting: a method of reroofing with new asphalt shingles over existing shingles in which the top edge of the new shingle is butted against the bottom edge of the existing shingle.

Net Free Vent Area: the area, measured in square inches, open to unrestricted air flow and commonly used as a yardstick to measure relative vent performance.

Night Seal (or Night Tie-Of0: a material and/or method used to temporarily seal a membrane edge during construction to protect the roofing assembly in place from water penetration. Usually removed when roofing application is resumed.

Nineteen-lach Selvage (Double-Coverage or Split-Sheet): a prepared roofing sheet with a 17 inch (430mm) granule surfaced exposure and a non-granule surfaced 19 inch (485mm) selvage edge. This material is sometimes referred to as SIS, double-coverage, or according to ASTM Standard D 371-89, Standard Specification for Asphalt Roll Roofing (Organic Felt) Surfaced with Mineral Granules, Wide Selvage.

Ninety-Pound: a prepared organic felt roll roofing with a granule surfacing that has a mass of approximately 90 pounds per 100 square feet, (4400 g/m2).

No-Cutout Shingles: shingles consisting of a single solid strip with no cutouts.

Non-Breathing Membrane: a membrane that does not allow significant amounts of water vapor or air to pass through; which has a perm rating 1.0 or less per ASTM E 96, Procedure E.

Non-Destructive Testing (NOT): a method to evaluate the disposition, strength, or composition of materials without damaging the object under test. Typically used to evaluate moisture content in roofing assemblies, the three common test methods are electrical capacitance, infrared thermography, and nuclear back-scatter.

Non-Flammable: liquid having no measurable flash point.

Non-Friable: a material that, when dry, cannot be crumbled, pulverized or reduced to powder by hand pressure.

Non-Oxidizing: a material which resists oxidation in exterior exposures or accelerated weathering.

Non-Traffic Bearing: for waterproofing purposes, a membrane system requiring some form of protection barrier and wearing surface.

Non-Volatile Content: that portion of a material that does not evaporate under normal ambient conditions.

Non-Vulcanized Membrane: a membrane manufactured from thermoplastic compounds that retains its thermoplastic properties throughout the service life of the membrane.

Nonwoven: a term used to describe the random arrangement of reinforcing fibers (glass, polyester, etc.) in a mat or scrim.

NRCA: National Roofing Contractors Association

NTRMA: National Tile Roofing Manufacturers Association

Nuclear Testing (Nuclear Back-Scatter): a device that contains a radioactive source to emit high velocity neutrons into a roof system. Reflecting neutrons are measured by a gauge that is used to detect moisture.

Nylon: generic name for a family of polyamide polymers, used as a scrim in some fabric-reinforced sheeting.