NAHB: National Association of Home Builders

Nailer: A piece of lumber that is secured to the roof deck, walls or to curbs. Nailers are used to receive fasteners for roof membranes. Generally, nailers are installed wherever it is necessary to secure flashings. Also see "Blocking".

Nailing Pattern: The pattern used to nail a roof component in place.

Neoprene: A synthetic rubber produced by polymerization of Chloroprene for use in liquid-applied and sheet-applied elastomeric roofing.

Nesting: To overlay existing shingles with new shingles and butt the top edge of the new shingle up against the bottom edge of the existing shingles.

Net Free Vent Area: The area permitting unrestricted air flow.

Night Seal: To temporarily seal the edge of a roof membrane in order to protect it from moisture entry. A.K.A. Night Tie-In or Water Cut-Off.

Ninety-Pound: Granule-surfaced or fiber glass or organic felt roll roofing that has a mass of approximately 90 pounds per 100 square feet.

Noble: In reference to metal, inert or inactive.

Non-Breathing Membrane: A membrane that does not permit water vapor or air to permeate it.

Non-Flammable: Material with no measurable flash point.

Non-Friable: Refers to a material’s inability to be crushed or pulverized into a powder.

Non-Volatile Content: The portion of a material that will not evaporate.

Non-Vulcanized Material: A material that retains its thermoplastic properties throughout its service life.

Non-woven: Random arrangement of the reinforcement fibers of a scrim sheet or mat.

NRCA: National Roofing Contractors Association.

NTRMA: National Tile Roofing Manufacturers Association


Open Time: The time after an adhesive has been applied and permitted to cure, during which the two surfaces can be bonded.

Open Valley: A valley where both sides of the roof are trimmed back from the centerline to expose the valley flashing material beneath. Either metal or mineral surfaced roll roofing is generally used as the flashing material.

Orange Peel Surface Texture: A surface with a texture comparable to the skin of an orange upon which a protective coating may be applied.

Organic: Formed from hydrocarbons or their derivatives, or of plant or animal origin.

Organic Felt: An asphalt roofing base material manufactured from organic fibers.

Organic Shingle: An asphalt shingle manufactured with a core of organic material.

OSB: Oriented Strand Board - Often used as roof sheathing in place of plywood.

Overlay: See "Recover".


Pallet: A platform used to hold materials.

Pan: (1) The concave piece of "Pan and Cover" tile whose rounded surface touches the top side of the roof substrate. (2) The flat part of a roofing panel located between the ribs.

Pan Flashing: A sheet metal flashing that covers an equipment platform and is designed to counter flash the base flashings surrounding the platform.

Parapet Wall: That part of a perimeter wall that extends above the roof elevation.

Penetration: An object that penetrates the roof structure, such as a plumbing vent pipe or electrical conduit.

Percent Elongation: The maximum amount that a material can be lengthened or stretched before breaking; expressed as a percentage of the original length of material tested.

Perlite: A natural volcanic glass aggregate used in lightweight insulating concrete and in preformed perlitic insulation boards.

Perm: A unit of water vapor transmission, defined as one grain of water vapor per square foot per hour per inch of mercury (Hg) pressure difference (1 inch of mercury = 0.491 psi).

Permeability: The rate of flow of a liquid or gas through a porous material.

pH: A measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing with increasing alkalinity and decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.

Phasing: Installing roof system components at separate time intervals. For instance, installing a base sheet, and then two plies of roofing one day, and coming back and installing the remaining two plies one or more days later.

Picture Framing: A grid pattern observed in a roof membrane. Generally follows the outline of underlying roof insulation boards.

PIMA: Polyisocyanurate Insulation Manufacturers Association

Pinhole: A small hole in a coating, foil, membrane, or other roofing material.

Pipe Boot: A prefabricated flashing component used to flash around pipe penetrations. Also known as a Roof Jack.

Pitch: (1) Term used to describe Roof Slope. (2) Slang for Coal Tar Pitch.

Pitch Pocket: A flanged piece of flashing material placed around irregularly shaped roof penetrations and filled with a sealing material to create a watertight seal around the penetration. Also referred to as a Pitch Box or Pitch Pan.

Pittsburgh Lock Seam: A method of interlocking two separate pieces of metal.

Plastic Cement: See "Flashing Cement".

Ply: A single layer of material in a roof membrane assembly. A four-ply built-up roof system would have four layers of felt adhered in alternate applications of bitumen. Today, some roof membranes, such as PVC, EPDM and modified bitumen, are installed in a single layer. These are referred to as “Single Ply” roof systems.

Pond: A puddle of water that does not drain off of a roof membrane.

Positive Drainage: A roof surface that slopes toward the drainage components in order to ensure complete drainage of the roof area within 48 hours of rainfall.

Primer: A thin, liquid bitumen or adhesive film applied to a surface to improve the adhesion of subsequent applications of bitumen or adhesive.


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