Roofing Glossary: N-Z

Last week, we began our roofing glossary with terms beginning with A-M. This week, we’ll focus the roofing glossary on the terms beginning from N through Z. We hope these help you understand your roof better.

N

Negative-side waterproofing – An application where the waterproofing system and the source of hydrostatic water pressure reside on opposite sides of the structural element.

Nesting – 1) Occurs when you install new metal roof deck on top of existing metal roof deck.  2) It’s a method of reroofing with new asphalt shingles over existing shingles where the top edge of the new shingle lies against the bottom edge of the new shingle.

Nonflammable – Does not easily ignite or catch on fire. If it does ignite, it will burn slowly.

NRCA – National Roofing Contractors Association.

O

Open time – The period of time after you apply an adhesive and allow it to dry during which an effective bond can be achieved by joining the two surfaces.

Organic – Being or composed of hydrocarbons or their derivatives. Of plant or animal origin.

Oxidation – 1) A weathering mechanism by which materials are exposed to the elements. Oxidation can be promoted by elevated temperature, UV rays, galvanic action and other items. 2) The loss of electrons by a constituent of a chemical reaction usually by the combination of oxygen with a reactant.

P

Parapet Wall – The part of a perimeter wall extending above the roof.

Permeability – 1) The time rate of vapor transmission through unit area of flat material of unit thickness induced by unit vapor pressure differences between the two surfaces under a specific temperature and humidity. 2) The property of a porous material that allows a liquid or gas to pass through it. It commonly refers to water vapor permeability of a sheet material or assembly. It’s defined as water vapor permeance per unit of thickness.

Permeance – 1) The time rate of water vapor transmission through unit area of flat material or construction induced by unit vapor pressure difference between two different surfaces under specified temperature and humidity.

Pigment – An insoluble compounding material that has color. It makes an item appear a certain color.

Pliability – The material property of being flexible or moldable.

Plywood – A flat panel built up sheets of wood called veneers, united under pressure by a bonding agent to create a panel with an adhesive bond between plies as strong as or stronger than the wood. Plywood is made of an odd number of layers with the grain of adjacent layers being perpendicular to each other. Layers may consist of a single ply or two or more plies laminated with parallel grain direction. Outer layers and all odd-numbered layers generally have the grain direction oriented parallel to the long dimension of the panel.

Ponding – An excessive accumulation of water at low-lying areas on a roof that remains wet after 48 hours since the precipitation occurred under conditions that are conducive to drying.

Positive drainage – Occurs when the design is set up for all loading deflections of the deck and an additional roof slope has been provided to ensure drainage of the roof area within 48 hours of precipitation.

Primary drainage – Drainage devices such as drains or scuppers that provide the direct removal of water from the roof’s waterproofing system.

R

Racking – Method of asphalt shingle application where shingles are placed vertically up the roof rather than laterally or across and up.

Re-cover – The process of installing an additional roof covering over an existing roof covering without removing that existing roof covering.

Roof covering – The exterior roof cover or skin of the roof assembly that consists of membrane, panels, sheets, shingles, tiles, etc.

Roof Slope – The angle a roof surface makes with the horizontal. This is expressed as a ratio of the vertical rise to the units of horizontal length. Slope may be expressed as a ratio or rise to run (ex. 4:12) or as an angle in degrees.

Rust – 1) A reddish material, primarily hydrated iron oxide; a corrosion product formed on iron or its alloys, resulting from exposure to humid atmosphere or chemical attack. 2) A special case of corrosion that deteriorates or alters the condition of the surface.

S

Scupper – A drainage device in the form of an outlet through a wall, a parapet wall or raised roof edge. It’s typically lined with a sheet-metal sleeve.

Sealant – 1) A material with adhesive and cohesive properties to form a seal. 2) A mixture of polymers, fillers and pigments used to fill and seal joints where moderate movement is expected. Unlike caulking, a sealant cures to a resilient solid.

Seam – A joint formed by bringing together two sections of material. Seams can be made and sealed in a variety of ways such as adhesive bonding, hot-air welding, solvent welding, adhesive tape and sealant.

Self-adhesive – A term used to describe materials with the ability to adhere to a variety of surfaces when contact is promoted by application of pressure but require no substance to form the bond.

Shingle – 1) A small unit of prepared roofing designed to install with similar units in overlapping rows or courses on inclines usually exceeding a 3:12 slope. 2) to cover with shingles 3) to apply any sheet material in succeeding overlapping rows like shingles.

Siding – The finish covering of an exterior wall of a frame building; siding may be comprised of cladding material like wood, aluminum or vinyl.

Solvent – Any liquid used to dissolve another material.

Span – The distance between supports or beams, girders or trusses.

Square – 1) A unit used in measuring area equivalent to 100 feet. 2) A quantity of material sufficient to cover 100 square feet of a roof deck.

Sump – An intentional depression around a roof drain or scupper to promote drainage.

Surfacing – The top layer or layers of a roof covering specified or designed to protect the underlying roofing from direct exposure to the weather.

T

Tar – a brown or black bituminous material, liquid or semi-solid in its consistency in which the predominating constituents are bitumens obtained as condensates in the processing of coal, petroleum, oil-shale, wood and other organic materials.

Tensile strength – The strength of a material under tension as distinct from torsion compression or shear.

Thermal insulation – A material applied to reduce the flow of heat.

Truss – A structure made up of three or more members that is usually in some form of triangular arrangement. Each member is designed to carry a tension or compression force. The truss then acts as beam.

U

Ultraviolet – aka UV, ultraviolet describes invisible electromagnetic radiation adjacent to the violet end of the visible spectrum. UV wavelengths range from 200 to 400 nanometers.

UV degradation – Damage done to a roof by the sun’s ultraviolet rays.

V

Vapor pressure – The pressure exerted by a vapor of a solid or a liquid when in equilibrium with the liquid or solid.

Vent – An opening designed to convey heat, air, water vapor or gas from inside a building to the atmosphere.

Viscous – Resistant to flow under stress.

W

Water-shedding roof system – A roof that depends on gravity for quick drainage of water to prevent its entry into or through the system of the roof.

Waterproof – The quality of a membrane, material or other component to prevent water entry.

Weld – To join pieces of material together by heat fusion.

There you have it, our roofing glossary is complete. We hope this helps you better understand your roof. If you still have questions about roofs, please give us a call at 512-219-0342. We’re happy to help.